Abstract1 Speciesaroundtheglobeareundergoingphenotypicshiftsatecologicallyrele-vanttimescalesastheyinvadenewecosystemsandrespondtochangingenviron-ments Disentangling the contribution of environmental gradients from theprocessofrangeexpansioninshapingthesechangesandidentifyingthespecifictraitsundergoingselectionarebothcritical toanticipatethesecondaryspreadandimpactofinvasivespecies
2 Herewe investigatephenotypic changes in rusty crayfish (Faxonius rusticus) anuisanceinvasivespeciesthroughanextensivesurveyoftheirinvasiongradientinmultipletributariesoftheJohnDayRiver(JDROregonUSA)amajortribu-taryoftheColumbiaRiver
4 Byaccountingforvariationsintemperatureprimaryproductivityandprey(mac-roinvertebrates) biomass throughout the invasion extent of rusty crayfish ourfindings suggest that lowconspecificdensitiesat the invasionedgeandspatialsortingprimarilydrivethesephenotypicchangesThetrendsobservedherearethus likely to intensify over time as rusty crayfish continues to rapidly spreadthroughouttheJDRandreachthemainstemColumbiaRiver
5 Ourstudyshowsthatphenotypicshiftscanmanifestrapidlyoverenvironmentalgradients experienced during the range expansion of aquatic invasive speciesPatternsinbothmorphologicalandfunctionaltraitsdocumentedintheJDRdem-onstratetheimportanceofbothenvironmentalfactorsanddispersalprocessesinshapingtheseresponsesinriverinenetworks
Speciesaround theglobeareexposed tochangingselectionpres-sures as they invade new landscapes or shift their range to trackenvironmentalchange(MoranampAlexander2014)Whentheirgeo-graphicdistributionshiftsorexpandstheindividualsinthevanguardof these populations often face novel environmental conditionspredators and competitors (ChuangampPeterson 2016)Mountingevidencesuggeststhatthesefactorsincombinationwithlowcon-specificdensitiesrelativetothoseexperiencedbycorepopulationspromoterapidchanges inspeciesphenotypesatrangeboundaries(ChuangampPeterson2016)
Phenotypic changes at the leading edge of invasive popu-lationsrsquo range have been observed in many taxonomic groupsincluding amphibians (eg cane toad Rhinella marina PerkinsPhillips Baskett amp Hastings 2013) insects (eg ground beetleMerizodus soledadinus Laparie Renault Lebouvier amp Delattre2013) fish (eg round gobyNeogobius melanostomus BrandnerCerwenka Schliewen amp Geist 2013) and decapods (eg signalcrayfishPacifastacus leniusculus HudinaHock Žganecamp Lucić2012)Thesechangeshavebeenmanifestedintraitsrangingfrombodylengthandfecunditytoboldness(ChuangampPeterson2016)andhavebeenassociatedwithacceleratedinvasionrates(PhillipsBrownampShine2010aWeiss-LehmanHufbauerampMelbourne2017) and increased impacts to recipient ecosystems (Brandneretal 2013 IacarellaDick amp Ricciardi 2015) Enhanced insightintotheprocessesleadingtophenotypicchangesininvasivespe-cies is thusessential foranticipating their futurespreadand im-pact(Phillips2015)aswellaspredictingtheoutcomeofspeciesrange shifts in response to climate change (Caplat etal 2013Travisetal2013)
Phenotypic plasticity (Davidson Jennions amp Nicotra 2011)natural selection (Brown Kelehear amp Shine 2013) and spatialsorting(ShineBrownampPhillips2011)arethethreedominantpro-cessesresponsibleforobservedtraitvariabilityatrangeedgesyettheirrespectivecontributionsareseldomunderstoodPhenotypicplasticitytheabilityformultiplephenotypestoarisefromasin-glegenotypeinresponsetochangingenvironmentalconditionsisparticularlyprevalentininvasivespecies(Davidsonetal2011)Itiscrucialinallowingpopulationstospreadandadapttochangingenvironments faster than would otherwise be possible by evo-lution through natural selection alone (Chevin Lande amp Mace2010)FurthermoreabioticandbioticforcesattheinvasionfrontcanleadtotraitevolutionbynaturalselectionLowintra-specificdensityat the leadingedge ismost likely toshift selectivepres-surestowardshighergrowthandreproduction(PhillipsBrownampShine2010b)Lastlytherangeexpansionprocessitselfcanleadtoadaptivechangesintraitsthroughspatialsortingwherebythefastestdispersingindividualsattheexpandingedgeofthepopula-tionsystematicallyinterbreedresultinginselectionforenhanceddispersalabilityintheiroffspringifdispersivetraitsareheritable(Shineetal2011)Thisrunawayprocesscontinuesinsubsequentgenerations until trade-offs between traits begin to limit the
potentialfordirectionalselection(BurtonPhillipsampTravis2010)althoughdispersalabilitymayevolveindependentlyofotherlife-historytraits(BonteampDahirel2017)Thetraits involvedinpro-motingdispersalandgrowthattheinvasionfrontaresonumerousthatnatural selectionandspatial sortingwhenenhancing thesetraits can impact morphology physiology behaviour immunol-ogy and life history among others (Chuang amp Peterson 2016)Understandingthespecifictraitsundergoingselectionininvasivespecies anddisentangling the influence of environmental condi-tions from contemporary evolution therefore requires empiricalstudiesthatarespecifictothespeciesandsystemsathand
Crayfishareamongthemostwidelyintroducedfreshwateran-imalsworldwide(Lodgeetal2012)Followingtheir introductionnon-native crayfish can cause severe ecological impacts acrossentirefoodwebstoagreaterextentthannativecrayfishbecauseliketheirnativecounterparts theyhavepolytrophic feedinghab-its but also often reach much greater densities and heightenedlevelsofforagingactivity(Hansenetal2013PintorampSih2009Twardochleb Olden amp Larson 2013) In invaded ecosystemsnative crayfish species can be displacedwithin a few years andpopulationsofmacrophytes insectssnailsandfishoftendecline(Bobeldyk amp Lamberti 2010 McCarthy Hein Olden amp VanderZanden2006OldenMcCarthyMaxtedFetzerampVanderZanden2006RosenthalStevensampLodge2006)Changes inpopulationstructure behaviour morphology and physiology have alreadybeen reportedbetweencoreandedgepopulations in severalon-going river invasions by crayfish (Hudina ZganecampHock 2015Hudinaetal2012PacircrvulescuPicircrvuMoroşanampZaharia2015RebrinaSkejoLucićampHudina2015)Atthebiogeographicalleveldifferences ingrowth survival feedinghabits andbehaviourarealsocommonamongcrayfishcongenersbetweentheirnativeandnon-nativerangefurtherdemonstratingthepotentialphenotypicchangeswroughtbytheinvasionprocess(GlonReisingerampPintor2018PintorampSih2009ReisingerElginTowleChanampLodge2017SargentampLodge2014)Even though theconsequencesofthesechangesoninvadedecosystemsoftenremainunexploredin-creasedinvasionratesalonecouldchallengeourabilitytorespondtonewandongoingcrayfish invasions Inadditiongiventhattheimpactofaninvasivespeciesontherecipientecosystemisnotonlya function of its range size but also of its abundance per-capitaeffect and other factors (Thomsen OldenWernberg Griffin ampSilliman 2011) changes in its somatic and reproductive growthratesor trophicnichecouldhavesevereconsequences fornativecommunitiesKnowledgeofthepotentialphenotypicshiftsoccur-ringatthefrontofcrayfishinvasionscouldthusshedlightonboththeselectionpressuresexertedupondispersingpopulationsandonthefutureimpactoftheseinvasions
Inthisstudyweinvestigatedchangesinrustycrayfish(Faxonius rusticusGirard1852previouslyOrconectes rusticusCrandallampDeGrave 2017) traits across their invasion gradient in the JohnDayRiver(JDR)theonlyknownoccurrenceofthisspecieswestoftheNorthAmericancontinentaldivide(OldenAdamsampLarson2009)andwheresecondaryspreadisongoing(MessagerampOlden2018)
emspensp emsp | emsp3MESSAGER And OLdEn
Our objective was two-foldWe first assessed whether rustycrayfish individuals displayed phenotypic differences progressingfromestablishedcorepopulationsnear the initial locationof theirintroduction to recently colonised invasion frontsWeused a riv-erscapesurveytoanalyserustycrayfishpopulationstructuremor-phology physiological condition and trophic position across itsrangeinthemainstemoftheJDRanditsmaintributariesWehy-pothesisedthatphenotypicchangesoccurredacrossrustycrayfishgenerations as they dispersed from their location of introductiontotheirpresent invasionfronts in theJDRWeexpectedthat lowconspecificdensitiesinnewlyinvadedriversectionswouldleadtoincreasedaccesstoresourcesandrelativeconsumptionofgrowth-inducingfoodlikemacroinvertebrates(HillSinarsampLodge1993)Wethusexpectedthatrustycrayfishwouldexhibitbetterphysiolog-icalconditionandhighertrophicpositionstowardtheinvasionfrontand as a result larger carapace length and higherweight (Brownetal2013)Wealsopositedthattwoadditionalmechanismscouldaffectcrayfishtraitvaluesduringrangeexpansion If larger fastergrowingandmorecompetitivecrayfisharebetterdispersersashas
beenreportedinmultipleinvasions(ChuangampPeterson2016)weexpectedtoobserveanincreaseincrayfishbodysizerelativechelalength andphysiological condition towards the invasion frontBycontrastiftrade-offsexistamongcrayfishtraitsthenselectionforhigh population growth rates and faster dispersal at the invasionleading edge could lead to unexpected changes in other trait val-ues(egdecreasedchelalength)towardstheinvasionfront(Phillipsetal2010b)
Wethenevaluatedwhetherthesephenotypicchangesinpopu-lationstowardstheinvasionfrontwerecausedbyplasticitytoenvi-ronmentalfactorsorselectionduetorangeexpansionWesoughttodisentanglethesetwosetsofprocessesbystudyingrustycray-fishsubpopulationsbothupstreamanddownstreamoftheir initiallocationofintroductionandbysimultaneouslyaccountingateachsiteforthedistancefromtheinvasioncore(reflectingtheinvasionstage at that location) gradients in environmental conditions andthe availability of food resourcesWe hypothesised that if selec-tion due to the range expansion process was driving changes inrustycrayfishtraitvaluesastheyspreadthroughouttheJDRthen
F IGURE 1emspRegionalmapoftheJohnDayRiverbasin(JDRinset)andrelativedensitiesofrustycrayfishalongthemainstemNorthForkandSouthForkoftheJDR(circlesize)withtheputativelocationofinitialintroduction(crayfishsymbol)CPUEcatchperuniteffort
TheJDRoriginatesintheBlueMountainsofnorth-easternOregon(USA) and runsundammed for457 river kmuntil its confluencewith the Columbia River just upstream from the Columbia RiverGorges(Figure1)Oneofthelargestfree-flowingriversintheUSAwithadrainageareaof21000km2theJDRisofhighconservationimportanceasitsupportsseveralfishspeciesofsignificantculturalandeconomicvalue includingendangeredspringChinooksalmonOncorhynchus tshawytschaandthreatenedsteelheadO mykiss
NativetotheOhioRiverbasinrustycrayfishisahabitatgener-alistitcaninhabitallsubstratesbutpreferscobblehabitatthrivesboth inareasofhighflowandstandingwatercanwithstandtem-peratures ranging fromclose to0degCup to35degCwith anoptimumnear 22degC and opportunistically consumes a variety of aquaticplants benthic invertebrates detritus periphyton fish eggs andsmall fish (Lorman1980MundahlampBenton1990)Maturerustycrayfishmateinlatesummerearlyfallorearlyspringandachievehighgrowthrates(BerrillampArsenault1984Lorman1980)
Rustycrayfishwas first found in the JDR in2005marking itsfirst recordedoccurrencewestoftheNorthAmericancontinentaldivide (Olden etal 2009) Evidence suggests that rusty crayfishwere first released in the late 1990s in themainstem JDR about
380kmupstreamfromitsconfluencewiththeColumbiaRivernearthe townofMountVernonOregonbya teacherandstudentsofa nearby school (Oldenetal 2009) In thec 20years since theirpresumeddateof introduction rusty crayfishhave rapidly spreadthroughouttheJDRcatchmentatratesexceeding15kmyearrais-ingconcernsthatthemainstemoftheColumbiaRivermaysoonbereached(MessagerampOlden2018)OnlythenativesignalcrayfishPacifastacus leniusculuswasknowntobepresent inthecatchmentprior to the introduction of rusty crayfish in the JDR (Larson ampOlden2011)PreviousstudiesandrecordsfromrotaryscrewtrapsoperatedbytheUSForestServiceshowthatsignalcrayfishwerewidespread throughout the JDR catchment despite low densitiesprior to the introductionof rusty crayfish (Sorenson2012DavidWoosterOregonStateUniversitypersonalcommunicationsAugust2013KeithDehartUSForestServicepersonalcommunicationsMarch2016)
22emsp|emspField data collection
Weimplementedaspatiallyextensivesurveyofrustycrayfishden-sities phenotypes and environmental conditions throughout itsinvasionrangetocapturegradientsinthesevariablesfromcoretoleading-edgepopulationsWeusedpredictionsofrustycrayfishdis-tribution inAugust 2016 from a spatially explicit individual-basedmodel (Messager amp Olden 2018) to distribute 60 sampling sitesevery5ndash10kmalongthemainstemandprimarytributariesoftheJDRencompassingtheinvasionextentofrustycrayfishSamplingwas conducted1ndash22August 2016 late enough in the summer sothat females would not be in berry young-of-the-year would belargeenoughtobesampledandalmostallmaturemaleswouldhavechangedtoareproductiveform(formI)withlargerchelaeinprepa-rationforfallmating(ButlerampStein1985Hamr1999Prins1968)
Toassesstherelativedensityofrustycrayfishacrossthecatch-mentarea-standardisedkick-seiningwasperformedinsixlocationsacross a 50-m long reach at each surveyed site One person dis-turbed 1 m2of substrateupstreamofa seinenetheldbyanotherteammember to flush crayfish downstream yielding amean andstandarddeviationofcrayfishdensityateachsiteToensurecon-sistencyinourmeasureofrelativedensityweexclusivelysampledin runs (ie rather than pools or riffles) when possible becauserunsprovidethewatervelocityanddepthneededforthissamplingmethodtobemosteffective(LarsonampOlden2016)Toavoidfalseabsencessnorkellinghand-nettingandbaitedtrapswerealsousedwhenrustycrayfishwerenotdetectedusingseining
Whererustycrayfishwerefoundthesexcarapacelength(mm)chelalength(mm)mass(g)missingchelae(yesno)andmoultingcon-dition(yesno)ofcapturedcrayfishweremeasuredateverysitewhiletwotissuesamples (abdominalwhitemuscle) from14rustycrayfishwere takenateveryothersiteRegeneratingchelae soft-shelledorvisibly smaller than the other chelawere notmeasuredWhenourstandardsamplingprotocolyieldedlt14crayfishadditionalspecimenswerecaughtbyhand-nettingsothatthesemeasurementsandtissuesamplescouldbetakenmdashalthoughtheseindividualswerenotincluded
F IGURE 2emspDensityofrustycrayfish(y-axis)asafunctionofdistancefromputativelocationofinitialintroduction(x-axis)inthemainstem(green)NorthFork(orange)andSouthFork(purple)JohnDayRiverCrayfishdensitiesareexpressedasthemean(points)and95confidenceinterval(bars)ofthecatchperuniteffort(CPUE)ThesmoothsolidlineandshadedregionrepresentthepredictedmeanCPUEand95BayesiancredibleintervalrespectivelyfromageneralisedadditivemodelVerticaldashedlinesrepresentconfluencesoftheSouthFork(at44km)andNorthFork(at87km)withthemainstemJohnDayRiver
emspensp emsp | emsp5MESSAGER And OLdEn
inourestimatesofrelativedensityWhencrayfishdensitywashighmorphologicalmeasurementswererecordedforarandomsubsampleof30ofthecrayfishthatwerecaughtbykick-seiningThefirsttissuesamplewasimmediatelystoredinnon-iodisedsaltforsubsequentδ15Nstableisotopeanalysistodeterminethetrophicpositionofrustycray-fishatthatsitemdashtheenergy-weightednumberoftrophicenergytrans-fersfromprimaryproducertocrayfish(VanderZandenampRasmussen1999) We also collected 12ndash20 mayfly nymphs (EphemeropteraHeptageniidae)inrunsandrifflesateachstudysitewherecrayfishtis-suesweresampledtocharacterisethebaselineδ15NvaluesofprimaryconsumersthroughouttheJDR(AndersonampCabana2007)Thesec-ondtissuesamplepreservedinRNAlaterregwasusedtoquantifytherelativeconcentrationofRNAandDNAinrustycrayfishcellsWhiletheamountofDNAremainsmostlyconstantincellsregardlessofcon-ditionstheamountofRNApositivelycorrelateswiththeamountofproteinsynthesis(anabolicactivity)ThereforetheratiooftheamountofRNAtothatofDNAinacellisaneffectiveeco-physiologicalindi-catorofcondition (hereafterphysiological condition) that reflects theorganismspotential investment in somatic growthandgametepro-duction (ie fertility) under a given set of environmental conditions(KoopWinkelmannBeckerHellmannampOrtmann2011)
Environmental conditions at each site were characterisedbymeasuringwater depth temperature and velocity aswell asbenthic chlorophyll a concentration of green algae and diatomsat 10 points along a transect perpendicular to the river banksThebenthic concentrationof chlorophylla is a proxyof benthicalgalbiomass (DoddsSmithampLohman2002)measuredusingaBenthotorch (Kahlert ampMcKie 2014) The biomass of macroin-vertebrateswas alsoquantified at all siteswhere crayfish tissuesamples were taken The abundance of macroinvertebrates wasassessedbytakingthree009-m2standardisedsamplesinrunsandriffleswithaD-framekicknetAllmacroinvertebratesampleswerethenwashedthrough05mmsievesandpreservedin70ethanol
23emsp|emspStable isotope analysis
Stable isotope analysiswas conducted on rusty crayfish tissuesand mayfly whole specimens to assess differences in crayfishfeedingpatterns throughout their invasiongradientAll sampleswerepreparedforisotopeanalysisusingstandardprotocolswiththeexceptionof the salt-basedpreservation a field-appropriatemethod that results inminimal anddirectionallyuniformeffectson δ13C and δ15N (Arrington ampWinemiller 2002) Prior to pro-cessingallcrayfishmuscletissuesandmayflywholebodieswererinsedwith distilledwater until the salt was dissolved Sampleswere then dried at 60degC for 24hr ground to powder and sentfornitrogenisotopeanalysistotheUniversityofCaliforniaDavisStableIsotopeFacilityThetrophicpositionofeachcrayfishatsite(S)wasestimatedaccordingto
where254istherustycrayfishdiscriminationfactororfractiona-tionfactor(Δ)representingtheabsolutedifferenceinδ15Nbetweenrusty crayfish and its diet determined in laboratory based on analgaediet(GlonLarsonampPangle2015)Weappliedasinglefrac-tionationfactortoalltrophiclinksofthefoodwebbetweenprimaryconsumersandcrayfishanddidnotaccountforfractionationdiffer-encesamongcrayfishdietsduetoalackofmorespecificreferencevalues
24emsp|emspRNADNA analysis
TheprocedurefortheextractionandquantitationofnucleicacidsinrustycrayfishtissueswasadaptedfromBerdaletRoldaacutenOlivarand Lysnes (2005) andVrede Persson andAronsen (2002) usingfluorochromesthatindiscriminatelybindtoDNAandRNAWepro-vide a brief description below but refer the reader to SupportingInformation AppendixS1 for a more detailed protocol BerdaletRoldaacutenandOlivar(2005)recommendusingthreeseparatealiquotsofeachsampletocomputethequantityofRNAandDNAincrus-taceantissuesthefirstassaymeasuresRNAafterDNAdigestionthesecondmeasuresDNAafterRNAdigestionandthethirdmeas-ures residual fluorescence after digestion of bothDNA andRNAFournucleicacidstandardcurveswithsixconcentrationseachwerethus run foreverybatchof samplesRNA+DNaseRNA+RNaseDNA+RNaseandDNA+DNaseToquantifyRNAandDNAfluo-rescence 50μl of diluted (1200) Quant-iTtrade RiboGreenreg reagentwas added to each platewell The slopes of the standard curveswerethenestimatedusinglinearregressionandthequantityofRNA(μgRNAmlassay)DNA(μgDNAmlassay)andtheirratioineachsample was calculated using the equations provided by BerdaletRoldaacutenandOlivar(2005)
25emsp|emspMacroinvertebrate biomass
Macroinvertebrate ash-free dry weight (AFDW)was estimated ateveryothersitealongthelengthoftheinvasiongradienttoreflectthepreybiomassavailableforconsumptionbyrustycrayfishoneofthemainenvironmentaldriversofcrayfishtrophicposition(Olssonetal 2008) Macroinvertebrates were sorted using a stereo mi-croscopeandseparatedfromothermaterial found inthesamplesSortedmacroinvertebrateswerethenrinsedwithdistilledwateranddriedinanovenat60degCfor48hrweighedcombustedinamufflefurnace at 550degC for 4hr (Mason LewisampWeber 1983) cooleddowntoroomtemperatureinadesiccatorfor6hrandreweighedAshmass (after combustion in furnace)was then subtracted fromdrymass(beforecombustion)toobtainAFDW
26emsp|emspData analysis
Thegoalof this studywas toassesswhetheraphenotypic shifthas occurred along the invasion gradient of rusty crayfish andwhether thisshift isbestexplainedby the rangeexpansionpro-cess or by longitudinal gradients in environmental conditions
(1)
Trophic positioncrayfishS
=2+
15NcrayfishSminus
(
sum3
mayfly=115Nmayfly S
)
∕3
254
6emsp |emsp emspensp MESSAGER And OLdEn
Environmentalconditionsandthespeedofrustycrayfishspreaddiffered among tributaries so each invasion leading edge wasanalysedseparately Intotalfour leading-edgepopulationswereanalysedonedownstreamedge in themainstemJDRand threeupstream edgesmdashin the mainstem South Fork and North ForkJDR(Figure1)
Sixtraitswereanalysedthroughouttheinvasionextentofrustycrayfish carapace length chela length weight trophic positionphysiologicalconditionandsexratio(theproportionofmalesatasite)Onlydataforcrayfishcaughtbykick-seininghand-nettingandsnorkellingwereincludedintheanalysisduetotheknownsizeandsexbiasoftrappingforlargemales(LarsonampOlden2016)Tocon-trolforthestrongrelationshipbetweenbodysizecrayfishweightandchelalengthduetoallometricgrowthresidualsfromcarapacelength-weightandcarapace length-chela lengthnon-linear regres-sionmodels developed separately for each sexwere used as re-sponsevariablesinthemodels(hereafterrelative weight and relative chela length)
A subset of the variablesmeasured at each site was selectedas potential environmental predictors of crayfish trait values theestimatednumberofdegreedays fromAugust2015 toJuly2016(degC)macroinvertebrate AFDW (mg) and chlorophyll a concentra-tion frombenthicgreenalgaeanddiatoms (μgChl-acm2)Degreedayswerecomputedbasedonwater temperatureestimated froma multiple regression model using satellite-measured daily land-surfacetemperaturecalendardaycatchmentareaandelevationaspredictorvariables (MessagerampOlden2018) In situ temperaturemeasurementswere not used in this analysis as diel temperaturevariationswereofthesameorderofmagnitudeasdifferencesbe-tween upstream and downstream sites Velocity and depth mea-surementswerenotincludedintheanalysiseitherduetotheirhighspatialvariabilityatbaseflowintheJDROnlythesitesforwhichallvariableshadbeenmeasuredwereincludedintheanalysisforatotalof18sites14sitesinthemainstemJDRtwointheSouthForkJDRandtwointheNorthForkJDR
In the South Fork andNorth Fork JDRwhere tissue samplesweretakenfromcrayfishinonlytwositesdifferencesintraitvaluesamongsiteswere testedusing two-sample t-testsanddifferencesinsexratiowereassessedwithYatesχ2testInthemainstemJDRgeneralisedadditivemodels(GAMs)weredevelopedtoanalysethedrivers of crayfish morphology physiological condition and tro-phicpositionGAMswerebuiltseparatelyfortwomaincategoriesofpredictorvariablesAfirstcategoryofmodelswasdevelopedtoaccountfortheroleoftherangeexpansionprocessindrivingphe-notypicchangesbyusingeachsitesdistancefromtheinitiallocationofrustycrayfishintroductionasthepredictorvariableThesecondmodel categorywas based on environmental variables thatmightinfluence trait valuesAdditionalmodelswerealsobuiltusingdis-tance from the initial introduction location togetherwith crayfishdensityandsex ratioaspredictorvariablesorcombiningmultipleenvironmentalvariablesThesignificanceandfitofcandidatemod-els(Akaikeinformationcriterionthep-valueofthecoefficientsandtheadjustedR2seeSupportingInformationTableS32)werethen
31emsp|emspCrayfish distribution and habitat conditions
Intotal1266crayfishwerecapturedacrossthe18sitesanalysedin thisstudyofwhich299weresampledformorphological traits259 forphysiological condition and254 for trophicpositionOursurveycombinedwithhistoricaldistributionrecordsandamodelofrustycrayfishspreadintheJDR(MessagerampOlden2018)showedthatrustycrayfishspreadatanacceleratingratesinceitsintroduc-tion and occupied at least 705km of river across the JDR catch-ment inAugust2016Bythatsummer ithadspreadnearly30kmupstreamintheNorthForkandSouthForkJDRandcolonisedthemainstem along a 250km stretch downstream of its introductionpoint(Figure1)Incontrasttoitsextensivespreaddownstreamtheupstreamspreadofrustycrayfishinthemainstemhadbeentempo-rarilyhaltedatthetimeofthesurveyduetoalow-headdam12kmupstream of the putative site of crayfish introduction Densitiesdownstream of the dam were similar to those found at the coreoftheir rangeTherefore theupstreammainsteminvasion leadingedgewasnotincludedinthisanalysisInadditionthepreciseloca-tionofthedownstreammainstemleadingedgecouldnotbedeter-minedduetolimitedaccesstotheriverthusthedownstream-mostsurveyedsitewhererustycrayfishwasfoundinthemainstemwastreatedasthedownstreamedgeoftheirrangeinthisstudy
There was a consistent decrease in rusty crayfish densitiesamongthesampledtributariesfromtheirinitiallocationofintroduc-tiontotheir invasionfrontsRustycrayfishdensities (measuredaskick-seiningcatchperuniteffortFigure2)werehighestinboththemainstem and South Fork JDR (gt30crayfishm2) 40ndash75kmdown-streamoftheinitialsiteofrustycrayfishestablishmentbutrapidlydroppedbyanorderofmagnitudebeyond60kmintheSouthForkJDRandbeyond80kminthemainstemandNorthForkJDRNativesignalcrayfishwerefoundinsympatrywithrustycrayfishinonlyafewsitesattheupstreaminvasionfrontswhererustycrayfishwerefound at lower densities (in the South Forkmainstem and othersmaller side tributaries of the JDR)Where native signal crayfishwerepresent theyoccurredatvery lowdensities (lt2crayfishm2) including in sites without rusty crayfish These findings togetherwithpastrecords (2013)ofsignalcrayfishoccurrence insympatrywithrustycrayfishatsiteswheresignalcrayfishwereabsentduringour2016surveysuggestthatsignalcrayfishisrapidlyexcludedfromsites invadedbyrustycrayfishas itspreadsacrosstheJDRcatch-mentThereforeinterspecificcompetitionwasnotconsideredasig-nificantmechanisminfluencingthetraitsinvestigatedinthisstudy
Temperature and macroinvertebrate biomass followed similarlongitudinalgradients fromupstreamtodownstreambetweenthemainstemSouthFork andNorthFork JDRwhereasbenthicbio-massofgreenalgaeanddiatomwerehighlyvariableamongtribu-taries (Supporting InformationFigureS21)Degreedays increased
emspensp emsp | emsp7MESSAGER And OLdEn
monotonically downstream while macroinvertebrate biomass de-creaseddownstreamTherewasalsoconsiderablevariabilityinmac-roinvertebrate biomass among adjacent sites including a suddenincreaseinbiomassdownstreamfromtheconfluenceofthemain-stemandtheNorthForkJDRwherelowcrayfishdensitiesprevailedGreenalgaeweresparsetoabsentinalltributariesThebiomassofdiatomsontheotherhandwashighestintheSouthForkandupper
mainstemJDR(upto45μgChl-acm2) and low in the lower main-stemandNorthForkJDRwith inconsistent longitudinalgradientsamongtributaries
32emsp|emspMorphology
Therewereconsistenttrendsinrustycrayfishmorphologyfromcore to leading-edge populations in all tributaries (Figure 4SupportingInformationAppendixS3)Therelativechelalengthof rusty crayfish in leading-edge populationswas significantlysmaller than those behind the front in all three tributaries(Mainstem GAM p=003 R2-adjusted=028 n=14 NorthFork t=217 df=29 p=004 South Fork t=303 df=42plt001 Figures3 and 4 Supporting Information TablesS31and S32) Crayfish density was also strongly and positivelyassociatedwith chela length across the JDR (MainstemGAMp=001 R2-adjusted=037 n=14 Figure4 SupportingInformation TableS32) No consistent difference was foundin mean carapace length between core and invasion frontpopulations of the JDR or betweenmale and female crayfishhowever there was a consistent decrease in carapace lengthvariance in thedirectionof the invasion inbothupstreamanddownstream dispersing populations (Figure4 SupportingInformationAppendixS3)Crayfishrelativeweightsignificantlydecreased towards the invasion front both downstream in themainstem (GAM p=004 R2-adjusted=025 n=14) and up-stream in the North Fork (W=177 p=001) and South Fork(W=328 p=001 Supporting Information FigureS41) alongwith decreasing crayfish density (Mainstem GAM p=002R2-adjusted=033 n=14 Figure4 Supporting InformationTableS32)Lastlytherewasnosignificanttrendinthepropor-tionofmalestowardsthefrontsoftheinvasiondespiteaslightincrease inmaledominance inbothupstreamanddownstreamleading edges when considering all sites where gt10 crayfishwerecaptured(SupportingInformationFigureS42)
EnvironmentalconditionswerenotstrongpredictorsofcrayfishmorphologythroughouttheirinvasiongradientDegreedaysdidnotcorrelateconsistentlyacross invasion frontswithanymorphologi-cal trait values (Figure4 Supporting Information TableS32) Forinstancewhiledecreasingupstream temperatureswerepositivelycorrelatedtorelativeweightintheSouthForkandNorthForkJDRtemperatureand relativeweightwerenegativelycorrelated in themainstemSimilarly inconsistentpatternswereobservedbetweentemperature and both relative chela length and carapace lengthMacroinvertebrate biomass (AFDW) was negatively but not sig-nificantly correlated with relative chela length and weight acrosstributariesandwasnotconsistentlyorsignificantlyassociatedwithshifts in carapace length across tributaries (Figure4 SupportingInformationTablesS31andS32)Finallywhilegreenalgaebiomasswasnotconsistentlycorrelatedwithanymorphologicaltraitvaluesdiatombiomasswaspositivelycorrelatedwithrelativechelalengthandweight throughout the JDR (Figure4 Supporting InformationTable S32)
F IGURE 3emspChangesinmeancrayfishrelativechelalength(a)trophicposition(b)andphysiologicalcondition(cRNADNAratioexpressingpotentialforsomaticgrowthandgameteproduction)alongtheinvasiongradientofrustycrayfishintheJohnDayRivercatchmentThesmoothsolidlineandshadedregionrepresentthepredictedmeantraitvalueand95Bayesiancredibleintervalrespectivelyfromageneralisedadditivemodelandasterisksdenotesignificantdifferencesinmean(ple001ple005)VerticaldashedlinesrepresenttheconfluencesoftheSouthFork(at44km)andNorthFork(at87km)withthemainstemJohnDayRiver
8emsp |emsp emspensp MESSAGER And OLdEn
33emsp|emspTrophic position
Thetrophicpositionofrustycrayfishwasconsistentlylowerforin-dividualsat invasion fronts than inpopulationscloser to thecoredespite wide variations among sites throughout the catchment
(Figures3band4SupportingInformationAppendixS3)Inthemain-stemrustycrayfishdietfirstincreaseddownstreamfromthattypi-calofasecondaryconsumeroromnivore(trophicpositionofc 3) to thatofatopcarnivore(trophicpositionofc4)andthendecreasedtowardsthefrontoftheinvasiondowntothatofaprimaryconsumer
F IGURE 4emspSummary of the relationshipsbetweenrustycrayfishtraitsandpredictorvariablesintheJohnDayRiver The direction and colour of the arrowsindicatethesignoftherelationship(egredupwardarrowsreflectpositiverelationships)betweenthepredictorvariable(columns)andthetrait(rows)foragiveninvasionleadingedge(downstreammainstemupstreamSouthForkorupstreamNorthFork)Greyarrowsshowstatisticallynon-significantrelationshipsSignificanceandaconsistentdirectionintherelationshipbetweencandidatepredictorsandtraitsamongtributariessuggestedtheprimacyofthatpredictorindrivingobserveddifferencesintraitsSeeSupportingInformationAppendixS3fordetailedstatisticalresultsFlatgreenarrowsshowvariablesforwhichtherewasnodifferenceamongsitesinthattributaryandrelationshipsdenotedbyandashwerenottestedduetoalackofhypothesisedmechanismsrelatingthevariablesdaggerAsh-freedryweight
Response variable Edge
Predictor variableDistance
from introduction
Crayfish density
Degree days
Macroinv AFDWdagger
Green algae Diatom
Relative chela length
Mainstem
South Fork
North Fork
Trophic position
Mainstem
South Fork
North Fork
Physiological Condition
(RNADNA)
Mainstem
South Fork
North Fork
Carapace length
Mainstem
South Fork
North Fork
Relative weight
Mainstem
South Fork
North Fork
Sex ratio( males)
Mainstemndash ndash ndash ndash ndash
South Forkndash ndash ndash ndash ndash
North Forkndash ndash ndash ndash ndash
Carapace length SD
Mainstemndash ndash ndash ndash
South Forkndash ndash ndash ndash
North Forkndash ndash ndash ndash
daggerAsh-free dry weight
emspensp emsp | emsp9MESSAGER And OLdEn
(trophicpositionofc2GAMp=005R2-adjusted=044n = 14 Figure3b) Therewas an equivalent drop in crayfish trophic posi-tionintheNorthForkJDRupstreamleadingedge(t=966df=22plt0001)butnoequivalentdecreaseintheSouthForkJDRleadingedgeTherewasnodifferenceintrophicpositionamongmaleandfemalecrayfishandalthoughtrophicpositionwasweaklycorrelatedwithcarapacelengthwithinsites(carapacelengthfixedeffect95CI=80times10minus3to19times10minus2trophiclevelmminlinearmixedeffectmodelwithsiteasrandomeffect)therewasnosignificantcorrela-tionbetweentrophicpositionandmeancarapacelengthacrosssitesalongthemainstemTrophicpositionwasnotsignificantlycorrelatedwithrelativechelalengthwithinsites(relativechelalengthfixedef-fect 95 CI=minus83times10minus3 to 23times10minus2 trophic levelmm in linearmixedeffectmodelwithsiteasrandomeffect)
Temperature increasing with downstream distance from theinvasionsourcewascorrelatedwithtrophicpositiononlytowardstheupstreaminvasionfrontsintheNorthForkandSouthForkJDR(Figure4Supporting InformationAppendicesS2andS3)Noneoftheotherenvironmentalvariablessignificantlycovariedwithtrophicpositioninaconsistentwayacrosstributaries(Figure4SupportingInformationAppendicesS2andS3)
34emsp|emspGrowth and condition
There was a consistent positive trend in rusty crayfish physi-ological condition (RNADNA ratio) towards invasion fronts alongwith decreasing crayfish densities (Figures3c and 4 SupportingInformationAppendixS3)Strongesttowardstheupstreamleadingedgesdespitedecreasing temperature (t-test SouthForkW=46p-value=001North Fork t=minus491df=155plt0001) the in-creaseinphysiologicalconditionwasonlymarginalinthemainstem[GAMp=019R2-adjusted=006n=14meanslope=63times10minus3 (95CI=minus27times10minus3to15times10minus2) [RNADNA]km]Thenegativecorrelation between crayfish physiological condition (RNADNAratio)andcrayfishdensityinthemainstemwasalsonon-significant(GAM p=043 R2-adjusted=minus003 n=14) Lastly environmen-tal variables (abiotic and biotic)were not consistently and signifi-cantlyassociatedwithRNADNAratioacrosstributaries(Figure4SupportingInformationAppendixS3)
4emsp |emspDISCUSSION
Thisstudyrevealedsignificanttrendsinmorphologicaltraitvaluesphysiologicalconditionandtrophicpositionofrustycrayfishfromtheirlocationofinitialintroductiontomultipleleadingedgesofinva-sionintheonlyknownpopulationofthisspeciesinwesternNorthAmericaEventhoughthesetrendswerenotconsistentlysignificantacrosstributariestheysuggestthatrustycrayfishindividualsatthevanguard of the invasion exhibited less competitive morphology(decreasedrelativeweightandchelalength)andexploitedenergeticpathwaysloweronthefoodchainyetwereinbetterphysiologicalcondition than individuals located closer to the invasion coreWe
contendthatthesephenotypicshiftsobservedinrustycrayfishareprobablydue to the rangeexpansionprocess itself rather than tonovelenvironmentalconditionsattheirrangeboundariesandthatthesetrendsmayintensifyastheinvasioncontinuestounfoldup-stream and downstream towards the main stem of the ColumbiaRiver
The observed decrease in crayfish relative chela length andweighttowardstheinvasionfrontscanbeattributedtothreemainreasonsmdashalthough further research is needed to confirm the re-spectivecontributionifanyofeachofthesemechanismsFirsttherangeexpansionofrustycrayfishmightbedrivenbytheexclusionof subdominant individuals from high-density population centresthereforeleadingtothewidespreadpresenceofcompetitivelyinfe-riorcrayfishattheinvasionleadingedge(HudinaHockampZganec2014)Inotherwordsindividualcrayfishwithlesscompetitivephe-notypesmayhavebeenforcedoutandsystematically interbredatthe invasionfront resulting in theaccumulationof relatively lightsmall-clawedindividualsattheleadingedgeInsupportofthismech-anismsignalcrayfishattheboundaryoftheirinvasionrangeacrossCroatiadisplaylowerlevelsofaggressionandoftenloseagonisticin-teractionstoindividualsfromtheinvasioncoredespitebeinginbet-ter physical condition (Hudinaetal 2015)However a significantincreaseinrelativeclawsizeawayfromsourcepopulationwasalsoobservedininvasivesignalcrayfishmalesoftheMuraRiverCroatia(Hudinaetal2012)Secondlargerchelaeandastouterbodyshapemay be associated with weaker dispersal ability and thus be se-lectedagainstthroughassociativematingofthefastestdispersersclusteredattheinvasionleadingedgeCrayfishwithshorterchelaeandmorefusiformbodyarebetterabletowithstandhighwaterve-locitiesassuggestedbymorphologicdifferencesbetweencrayfishfound in high-velocity streams compared to those in low-velocitystreams and lakes (Perry etal 2013) Becausewater velocities inexcessof03ndash05msleadtodecreasedcrayfishmovementandpo-tentially increasedenergyexpenditureincrayfish(ClarkKershnerampHolomuzki 2008Matheramp Stein 1993 Perryamp Jones 2017)individualswithshorterchelaeandmorefusiformbodiesmaythusbeabletodisperseforlongerperiodsoftheyearintheJDRwhosedischarge isunregulatedbydamsandflowregimeischaracterisedbyspringsnowmeltThirdlowrustycrayfishconspecificdensitiesat invasion front sitesmay relax the constraints imposedby com-petitioninhigh-densityareasandthusreducetherequirementforinvestment in traitsassociatedwithcompetitionShelterandfoodlimitationsarethemaindriversofagonisticinteractionsincrayfish(BergmanampMoore2003CapelliampHamilton1984)Whentheseresourcesareplentiful inpioneerpopulationsbehaviouralpheno-typesassociatedwithlargeclawsandweightaspartofanaggressionsyndrome(Hudinaetal2012)couldthereforeleadtounnecessaryenergyexpensesand reduced foraging leading to reduced fitness(SihCoteEvansFogartyampPruitt2012)Thusashiftinselectivepressuremayhave led toachange in rustycrayfish lifehistoryattheedgeoftheinvasion involvingthereallocationofenergyfromallometricgrowthofcompetitivetraitstoreproductionanddisper-saltraitsnotmeasuredhere(egwalkingleglength)(Phillipsetal
Weconjecturethatashift intheselectionregimeexperiencedbyrustycrayfishfromcoretoleading-edgeareasisthemostprob-ableexplanationforthetrends inrelativechela lengthandweightobservedinthisstudyHoweverwithoutknowledgeoftheheritabil-ityofthecrayfishtraitsexaminedinthisstudyinferenceregardingthespecificmechanisms inoperation isstill limitedTheaccelerat-ingrateofspreadofrustycrayfish intheJDRthe lowpopulationdensities observedwithin several kilometres of the upstream anddownstreaminvasionfrontsandhighphysiologicalfitnessininva-sionfrontpopulationssuggestthatapushedinvasionexcludingsub-dominantcrayfishfromhigherdensityareasisunlikelytoexplaintheobservedtraitdifferencesMoreoverthereislittletonoevidenceoftheinfluenceofchelasizeorrelativebodyweightondispersalspeed(KamranampMoore 2015) Lastly the difference in relativeweightandchelalengthbetweeninvasioncoreandfrontpopulationscouldalsobedrivenbynaturalselectioninhighcrayfishdensitycorepop-ulationsHistoricaldatafromSorenson(2012)combinedwiththisstudy shownodifference inchela length (Supporting InformationFigureS51)butasignificantincreaseinrelativeweightfrom2010to2016atthepresumedsiteofrustycrayfishintroduction(SupportingInformationFigureS52)Thechangesintraitvaluesobservedherearethuslikelytobetheresultsofacombinationofdriversincludingreducedfitnessofcompetitivephenotypesatlowcrayfishdensityselectionforhighrelativeweightinthepopulationcoreandtrade-offsbetweenthesecompetitiveattributesandother traitsassoci-atedwithhigherdispersalability
Theobserved increase in rustycrayfishanabolicactivitymea-suredasRNADNAinleading-edgepopulationsoftheJDRalthoughweak in themainstem indicates that the rangeexpansionprocesshas led to greater somatic growth andor reproductive potentialin pioneer individuals This pattern matches several documentedincreases inbodyconditiongrowthandreproductivepotential insimilarstreaminvasionsbothwithinasingleinvasiongradientandbetweennativeandnon-nativepopulationsWithintheirnon-nativerange invasion front signal crayfish in Croatia and female spiny-cheekcrayfish in theDanubebothdisplayedgreater reproductivepotentials than their counterparts in core areas with the formeralsobeinginbetterconditionandenergeticstatus(Pacircrvulescuetal2015Rebrinaetal2015)Whencomparingnativeandnon-nativepopulationsofrustycrayfishbothlakeandmesocosmexperimentsfoundthatnon-nativeindividualshavehighergrowthratesandlevelsofactivitythantheirnativecongeners(PintorampSih2009Sargentamp Lodge 2014) Nonetheless whether the observed increase inrustycrayfishphysiologicalconditiontowardstheinvasionfront isassociated with greater somatic growth rates or gamete produc-tionremainsunresolvedandwarrantsfurtherinvestigationIndeed
simultaneous increases inconditiongrowthandreproductivepo-tentialarenotuniversalbecauseselectionfordispersalabilityduringrangeexpansionmay lead tounexpected trade-offsFor instancetadpolesandjuvenilesininvasionfrontpopulationsofcanetoadsintropicalAustraliagrowupto31fasterthanthosefromlongeres-tablishedpopulations(Phillips2009)andadultsdemonstratehigherfeeding rates larger fat stores andbetter condition thanconspe-cifics in later invasion stages (Brownetal2013)However lowerreproductiverateshavealsobeendocumentedincanetoadinvasionfrontpopulations(HudsonPhillipsBrownampShine2015)
Itmightseemthathighercrayfishgrowthratestowardstheinva-sionfrontscontradicttheobservedpatternsofreducedweightandchelalengthobservedinpioneercrayfishHoweverselectionforafasterlifestylecoulddecreaseageatmaturityandshortenthelifes-panoftheseinvasionfrontcrayfishwhileselectingagainstallome-tricgrowthofcompetitivemorphologyBothcrayfishgrowth rateandfecundityaredensitydependent(GuanampWiles1999MomotampGowing1977)Thereforeitispossiblethathighgrowthandfe-cundityphenotypeshavearisenfromnaturalselectioninthec 15 generationssincetheirintroductionaspartofadispersalsyndromeassociating rapid development and high fecunditywith dispersivetraits(RonceampClobert2012Stevensetal2013)
Rustycrayfishattheleadingedgesoftheirdistributionallimitsappeartobefeedinglowerinthefoodwebwhencomparedtocon-specifics locatedbehind the invasion frontThispattern stands incontradictionwithmostpreviousstudiesofstreaminvasionsRoundgobiesattheedgeoftheirexpandingrangeconsumemoreoftheirfavouredpreytypethanincentralpopulations(RabyGutowskyampFox2010)andhavehigherδ15Nsignaturesthanthepreviousyearfront(Brandneretal2013)Invasionfrontbloodyredmysidshrimp(Hemimysis anomala)werenotmoreselectiveintheirpreyconsump-tionbutshowedgreaterabilitytolocateandcapturezooplanktonprey than those shrimp in corepopulations (Iacarella etal 2015)ForcrayfishinvasionstrophicnicheshiftshaveonlybeenassessedatthebiogeographicalscaleandoffermixedinsightsInagreementwithourfindingsnon-nativepopulationsofrustycrayfishandvirilecrayfish(Faxonius virilis)appearedtoshowgreaterratesofalgaecon-sumption (despite constant macroinvertebrate prey consumption)thandidnativepopulationsinlaboratoryassays(Glonetal2018)By contrast an intercontinental stable isotope analysis revealedtrophicnicheconservatisminsignalcrayfishbetweenitsnativeandnon-native range (LarsonOldenampUsio 2010) Trophic flexibilityhasbeenshowntobespecies-dependenteveninsympatricnativecrayfishspecies (JohnstonRobsonampFairweather2011)andmaythus not be a consistent characteristic among invasive omnivoreseitherItisunlikelythatcannibalismawidespreadphenomenonincrayfishpopulations(GuanampWiles1998) ledtotheobservedin-creaseintrophicpositioninareaswithhighdensitiesofcrayfishasconspecificdensitywasnotcorrelatedtotrophicpositionintheJDR(Figure4SupportingInformationAppendixS3)Lastlyitisunlikelythatnon-crayfishpredatorsandcompetitorscouldhavedriventhisdownwardshiftinthetrophicpositionofrustycrayfishasthisshiftwasobservedacrossboththedownstream(increasingfishdensity)
Rustycrayfishhada lower trophicpositionevenwhenmacro-invertebrateprey availability increased towards the invasion frontintheNorthForkJDRThispatterncontrastedwithpastevidenceof a positive relationship between macroinvertebrate availabilityand crayfish trophic position (Olsson etal 2008) and greater as-similation efficiencies of invertebrates than other food items bycrayfish (WhitledgeampRabeni 1997)However the lackof signifi-cantdecreaseintrophicpositiontowardstheinvasionfront intheSouth Fork JDR could be due to a counter-effect from increasingmacroinvertebrate biomass upstream Consumption of macroin-vertebrateshasbeen linkedto increases inweightgainandmeta-bolicrates(BondarBottriellZeronampRichardson2005Hilletal1993 McFeeters Xenopoulos Spooner Wagner amp Frost 2011)Nevertheless in these same studies juvenile signal crayfish in anatural settingdisproportionatelyconsumedfoodtypes thatweretheoppositeofthoseshowntobeofmostnutritionalvaluetothem(Bondar etal 2005) and rusty crayfishmortalitywashigheron adietbasedoninvertebratethanoneonperiphytonordetritus(Hilletal 1993) This suggests that high growth might be associatedwith greater physiological stress due tomore frequentmoultingandhigherforagingcostsinnaturalsettingsThuswehypothesisethatenergyintakeandlong-termfitnessofrustycrayfishassociatedwithperiphytonanddetritusconsumptionmaybehigherthanwithmacroinvertebratedietsdespitetheir lowerdigestionefficiencyoftheseresources
Trade-offs can also arise between increased dispersal rates atrangemarginsand the functional responseof thenon-nativecon-sumer due to the high cost of dispersal (Fronhofer amp Altermatt2015)Giventheircurrentrateofspread(c20kmyeardownstreamfrom2010to2016)intheJDR(MessagerampOlden2018)andawin-dowofactivityof8ndash9months(basedonwatertemperaturesinthemainstem)rustycrayfishwouldhavetoachieveanetdownstreamspreadrateof80mdayonaveragewithoutconsideringtimeded-icatedtomatingandjuvenileparentalcareWespeculatethatthispacecouldrestricttheamountoftimeavailableforactivelypreyingoninvertebratesandcouldselectforthosecrayfishbestabletoef-ficientlyfeedandgrowonabundantandaccessiblebasalresourcesIthasalsobeenhypothesisedforstreamfishesthatthosenon-nativespeciesthatcansustaingrowthandreproductiononlow-qualityre-sourcesshouldbebestabletobecomeestablished(GidoampFranssen2007) Incrayfishabroader trophicniche thatexpandedtowardslower trophic levelsmayhaveaffordedcompetitiveadvantages totheintroducedsignalcrayfishoverthenativenoblecrayfishAstacus astacus inSwedishstreams (OlssonStenrothNystromampGraneli2009) Therefore our findings that rusty crayfish at the invasionfrontactmostlyasprimaryconsumerswhileachievinggreaterphys-iologicalconditionmightreflectanincreaseinfeedingefficiencyonbasal resources as a by-product of greater dispersal ability devel-opedthroughtheirrangeexpansionintheJDR
a crucial first step towards developing spatially explicit strategiestocontrol this invasion If thedocumentedphenotypicshifts fromcore to invasion front populations are indeed associatedwith theaccelerating rateof spreadof rusty crayfish then targeting thoseindividualsattheinvasionleadingedgeforremoval(egbytrapping)mightconstraintheaccumulationofdispersivephenotypesintheseareasAccountingforthesephenotypicshiftsinmechanisticmodelsofinvasivespread(egMessagerampOlden2018)couldalsoprovideuswithavirtual laboratorytotesttheeffectivenessofalternativecontrolstrategiesincontainingthespreadofriverineinvaderssuchasrustycrayfish
Our results suggest that low conspecific densities and spatialsortinginleading-edgepopulationsledtoashift inthephenotypeofrustycrayfishtowards lowercompetitiveabilityhigher intrinsicgrowthandorreproductionandgreaterforagingefficiencyonbasalresourcesastheyspreadupstreamanddownstreamintheJDROurstudydesignenabledustolinkmorphologicalandfunctionaltraitstobetterexploretheconsequencesofthisrangeexpansiononinvadedecosystemsWeexpectthatthediminishedcompetitiveabilityob-servedinthevanguardofthisrustycrayfishinvasionmightleadtoreducedfitnessoftheinvasionfrontphenotypesoncedensities innewlycolonisedareas limit theavailabilityofshelterand intensifycompetition formatesThe long-termevolutionary implicationsofthesephenotypicshiftsmightthusbelimited(PerkinsBoettigerampPhillips2016)Howeverthetrophicshiftobservedininvasionfrontpopulationscouldalsoallowrustycrayfishtoreachhigherdensitiesintheseareasastheymightexploitresourcesmorebroadlyandeffi-cientlyundercompetitiveconditionsTheevolutionaryforcesatplayinthisinvasionhaveprobablyinteractedwithlongitudinalgradientsinenvironmentalconditionsinwaysanalogoustothoseexperiencedbyspeciesduringtheirmigrationtowardscoolerareasunderclimatechangeIntegratingthestudyofmorphologicalandfunctionaltraitswith spatial variation in environmental conditions thus provides arobustwaytoassesswhethercontemporaryevolutionisalteringthephenotypeandecosystemimpactsofspeciesastheirrangeexpandsthroughthelandscape
Inconclusionthisstudyaddsevidenceinsupportofphenotypicchangesexpectedinnon-nativeorganismsexposedtochangingse-lectionpressuresas they invadenewenvironmentsDisentanglingthe causes of these changes whether related to environmentalfactorsorselectionduetorangeexpansionremainsan importantareaofinvestigationasweseektobetterunderstandtheecologicalimpactsofinvasivespeciesandhownativespecieswillrespondtoshiftingenvironmentalconditionsinthefuture
ACKNOWLEDG MENTS
WethankJeffAdamsEricLarsonDavidWoosterStephenBollensandKeithSorensonforprovidinghistoricaldataforrustycrayfishthe staff at theGrantCountyAssessorsoffice and the JohnDayFossilBedsNationalMonument for their help accessing the riverParticular appreciation goes to all the landowners throughout theJohnDayRiverbasin foraccess to their landandsupport for this
12emsp |emsp emspensp MESSAGER And OLdEn
projectWearegratefultoJacobCrunkforhisinestimablehelpwithfieldworkandEthenWhattamforhishelpprocessingmacroinver-tebratesamplesFromtheUniversityofWashingtonwethanktheMolecularEcologyResearchLaboratory(MERLab)andmorespecifi-callyIsadoraJimenez-HidalgoandNatalieLowelltheOldenlabaswellasJoshuaLawlerThomasQuinnandPatrickTobinThemanu-scriptwasimprovedbythecommentsfromtwoanonymousreview-ersFundingsupportwasprovidedbytheJohnNCobbScholarshipin Fisheries the Simpson Award from the Society for FreshwaterScienceandtheCrustaceanSocietyfellowshipinGraduateStudiesawarded to MLM and the University of Washington H MasonKeelerEndowedProfessorshipawardtoJDO
Mathis L Messager httpsorcidorg0000-0002-3051-8068
Julian D Olden httpsorcidorg0000-0003-2143-1187
R E FE R E N C E S
AndersonCampCabanaG (2007)Estimatingthetrophicpositionofaquatic consumers in river food webs using stable nitrogen iso-topes Journal of the North American Benthological Society 26(2)273ndash285 httpsdoiorg1018990887-3593(2007)26[273ettpoa]20co2
Arrington D A ampWinemiller K O (2002) Preservation effects onstable isotope analysis of fishmuscleTransactions of the American Fisheries Society131(2)337ndash342httpsdoiorg1015771548-8659(2002)131lt0337peosiagt20co2
Berdalet E Roldaacuten C ampOlivarM P (2005) Quantifying RNA andDNAinplanktonicorganismswithSYBRGreenIIandnucleasesPartBQuantification in natural samplesScientia Marina69(1) 17ndash30httpsdoiorg103989scimar200569n117
BerdaletERoldaacutenCOlivarMPampLysnesK (2005)QuantifyingRNAandDNAinplanktonicorganismswithSYBRGreenIIandnu-cleases Part A Optimisation of the assay Scientia Marina 69(1)1ndash16httpsdoiorg103989scimar200569n11
Bobeldyk A M amp Lamberti G A (2010) Stream food web re-sponses to a large omnivorous invader Orconectes rusticus (Decapoda Cambaridae) Crustaceana 83(6) 641ndash657 httpsdoiorg101163001121610x491031
BondarCABottriellKZeronKampRichardsonJS(2005)Doestro-phicpositionof theomnivoroussignalcrayfish (Pacifastacus lenius-culus) inastreamfoodwebvarywith lifehistorystageordensityCanadian Journal of Fisheries and Aquatic Sciences62(11)2632ndash2639httpsdoiorg101139f05-167
BrandnerJCerwenkaAFSchliewenUKampGeistJ(2013)BiggerisbetterCharacteristicsofroundgobiesforminganinvasionfrontinthe Danube River PLoS ONE8(9)e73036httpsdoiorg101371journalpone0073036
BrownGPKelehearCampShineR (2013)Theearly toadgets theworm Cane toads at an invasion front benefit from higher preyavailability Journal of Animal Ecology 82(4) 854ndash862 httpsdoiorg1011111365-265612048
Burton O J Phillips B L amp Travis J M J (2010) Trade-offs and the evolution of life-histories during range ex-pansion Ecology Letters 13(10) 1210ndash1220 httpsdoiorg101111j1461-0248201001505x
Capelli G M amp Hamilton P A (1984) Effects of food shelter andtimeof dayon aggressive activity in the crayfishOrconectes rusti-cus(Girard)Journal of Crustacean Biology4(2)252ndash260httpsdoiorg1011631937240x84x00363
Caplat P Cheptou P O Diez J Guisan A Larson B MMacDougall A S hellip Zhang R (2013) Movement impacts andmanagement of plant distributions in response to climate changeInsights from invasions Oikos 122(9) 1265ndash1274 httpsdoiorg101111j1600-0706201300430x
Chuang A amp Peterson C R (2016) Expanding population edgesTheories traits and trade-offsGlobal Change Biology22(2) 494ndash512httpsdoiorg101111gcb13107
ClarkJMKershnerMWampHolomuzkiJR(2008)Grainsizeandsorting effects on size-dependent responses by lotic crayfish tohigh flows Hydrobiologia 610 55ndash66 httpsdoiorg101007s10750-008-9422-0
CrandallKAampDeGraveS (2017)Anupdatedclassificationofthefreshwater crayfishes (Decapoda Astacidea) of the world with acompletespecieslistJournal of Crustacean Biology37(5)615ndash653httpsdoiorg101093jcbiolrux070
DavidsonAMJennionsMampNicotraAB(2011)Doinvasivespe-cies show higher phenotypic plasticity than native species and ifso is it adaptiveAmeta-analysisEcology Letters14(4) 419ndash431httpsdoiorg101111j1461-0248201101596x
DoddsWK Smith VH amp Lohman K (2002)Nitrogen and phos-phorusrelationshipstobenthicalgalbiomassintemperatestreamsCanadian Journal of Fisheries and Aquatic Sciences 59(5) 865ndash874httpsdoiorg101139f02-063
Fronhofer E A amp Altermatt F (2015) Eco-evolutionary feedbacksduring experimental range expansions Nature Communications 66844httpsdoiorg101038ncomms7844
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
2emsp |emsp emspensp MESSAGER And OLdEn
1emsp |emsp INTRODUC TION
Speciesaround theglobeareexposed tochangingselectionpres-sures as they invade new landscapes or shift their range to trackenvironmentalchange(MoranampAlexander2014)Whentheirgeo-graphicdistributionshiftsorexpandstheindividualsinthevanguardof these populations often face novel environmental conditionspredators and competitors (ChuangampPeterson 2016)Mountingevidencesuggeststhatthesefactorsincombinationwithlowcon-specificdensitiesrelativetothoseexperiencedbycorepopulationspromoterapidchanges inspeciesphenotypesatrangeboundaries(ChuangampPeterson2016)
Phenotypic changes at the leading edge of invasive popu-lationsrsquo range have been observed in many taxonomic groupsincluding amphibians (eg cane toad Rhinella marina PerkinsPhillips Baskett amp Hastings 2013) insects (eg ground beetleMerizodus soledadinus Laparie Renault Lebouvier amp Delattre2013) fish (eg round gobyNeogobius melanostomus BrandnerCerwenka Schliewen amp Geist 2013) and decapods (eg signalcrayfishPacifastacus leniusculus HudinaHock Žganecamp Lucić2012)Thesechangeshavebeenmanifestedintraitsrangingfrombodylengthandfecunditytoboldness(ChuangampPeterson2016)andhavebeenassociatedwithacceleratedinvasionrates(PhillipsBrownampShine2010aWeiss-LehmanHufbauerampMelbourne2017) and increased impacts to recipient ecosystems (Brandneretal 2013 IacarellaDick amp Ricciardi 2015) Enhanced insightintotheprocessesleadingtophenotypicchangesininvasivespe-cies is thusessential foranticipating their futurespreadand im-pact(Phillips2015)aswellaspredictingtheoutcomeofspeciesrange shifts in response to climate change (Caplat etal 2013Travisetal2013)
Phenotypic plasticity (Davidson Jennions amp Nicotra 2011)natural selection (Brown Kelehear amp Shine 2013) and spatialsorting(ShineBrownampPhillips2011)arethethreedominantpro-cessesresponsibleforobservedtraitvariabilityatrangeedgesyettheirrespectivecontributionsareseldomunderstoodPhenotypicplasticitytheabilityformultiplephenotypestoarisefromasin-glegenotypeinresponsetochangingenvironmentalconditionsisparticularlyprevalentininvasivespecies(Davidsonetal2011)Itiscrucialinallowingpopulationstospreadandadapttochangingenvironments faster than would otherwise be possible by evo-lution through natural selection alone (Chevin Lande amp Mace2010)FurthermoreabioticandbioticforcesattheinvasionfrontcanleadtotraitevolutionbynaturalselectionLowintra-specificdensityat the leadingedge ismost likely toshift selectivepres-surestowardshighergrowthandreproduction(PhillipsBrownampShine2010b)Lastlytherangeexpansionprocessitselfcanleadtoadaptivechangesintraitsthroughspatialsortingwherebythefastestdispersingindividualsattheexpandingedgeofthepopula-tionsystematicallyinterbreedresultinginselectionforenhanceddispersalabilityintheiroffspringifdispersivetraitsareheritable(Shineetal2011)Thisrunawayprocesscontinuesinsubsequentgenerations until trade-offs between traits begin to limit the
potentialfordirectionalselection(BurtonPhillipsampTravis2010)althoughdispersalabilitymayevolveindependentlyofotherlife-historytraits(BonteampDahirel2017)Thetraits involvedinpro-motingdispersalandgrowthattheinvasionfrontaresonumerousthatnatural selectionandspatial sortingwhenenhancing thesetraits can impact morphology physiology behaviour immunol-ogy and life history among others (Chuang amp Peterson 2016)Understandingthespecifictraitsundergoingselectionininvasivespecies anddisentangling the influence of environmental condi-tions from contemporary evolution therefore requires empiricalstudiesthatarespecifictothespeciesandsystemsathand
Crayfishareamongthemostwidelyintroducedfreshwateran-imalsworldwide(Lodgeetal2012)Followingtheir introductionnon-native crayfish can cause severe ecological impacts acrossentirefoodwebstoagreaterextentthannativecrayfishbecauseliketheirnativecounterparts theyhavepolytrophic feedinghab-its but also often reach much greater densities and heightenedlevelsofforagingactivity(Hansenetal2013PintorampSih2009Twardochleb Olden amp Larson 2013) In invaded ecosystemsnative crayfish species can be displacedwithin a few years andpopulationsofmacrophytes insectssnailsandfishoftendecline(Bobeldyk amp Lamberti 2010 McCarthy Hein Olden amp VanderZanden2006OldenMcCarthyMaxtedFetzerampVanderZanden2006RosenthalStevensampLodge2006)Changes inpopulationstructure behaviour morphology and physiology have alreadybeen reportedbetweencoreandedgepopulations in severalon-going river invasions by crayfish (Hudina ZganecampHock 2015Hudinaetal2012PacircrvulescuPicircrvuMoroşanampZaharia2015RebrinaSkejoLucićampHudina2015)Atthebiogeographicalleveldifferences ingrowth survival feedinghabits andbehaviourarealsocommonamongcrayfishcongenersbetweentheirnativeandnon-nativerangefurtherdemonstratingthepotentialphenotypicchangeswroughtbytheinvasionprocess(GlonReisingerampPintor2018PintorampSih2009ReisingerElginTowleChanampLodge2017SargentampLodge2014)Even though theconsequencesofthesechangesoninvadedecosystemsoftenremainunexploredin-creasedinvasionratesalonecouldchallengeourabilitytorespondtonewandongoingcrayfish invasions Inadditiongiventhattheimpactofaninvasivespeciesontherecipientecosystemisnotonlya function of its range size but also of its abundance per-capitaeffect and other factors (Thomsen OldenWernberg Griffin ampSilliman 2011) changes in its somatic and reproductive growthratesor trophicnichecouldhavesevereconsequences fornativecommunitiesKnowledgeofthepotentialphenotypicshiftsoccur-ringatthefrontofcrayfishinvasionscouldthusshedlightonboththeselectionpressuresexertedupondispersingpopulationsandonthefutureimpactoftheseinvasions
Inthisstudyweinvestigatedchangesinrustycrayfish(Faxonius rusticusGirard1852previouslyOrconectes rusticusCrandallampDeGrave 2017) traits across their invasion gradient in the JohnDayRiver(JDR)theonlyknownoccurrenceofthisspecieswestoftheNorthAmericancontinentaldivide(OldenAdamsampLarson2009)andwheresecondaryspreadisongoing(MessagerampOlden2018)
emspensp emsp | emsp3MESSAGER And OLdEn
Our objective was two-foldWe first assessed whether rustycrayfish individuals displayed phenotypic differences progressingfromestablishedcorepopulationsnear the initial locationof theirintroduction to recently colonised invasion frontsWeused a riv-erscapesurveytoanalyserustycrayfishpopulationstructuremor-phology physiological condition and trophic position across itsrangeinthemainstemoftheJDRanditsmaintributariesWehy-pothesisedthatphenotypicchangesoccurredacrossrustycrayfishgenerations as they dispersed from their location of introductiontotheirpresent invasionfronts in theJDRWeexpectedthat lowconspecificdensitiesinnewlyinvadedriversectionswouldleadtoincreasedaccesstoresourcesandrelativeconsumptionofgrowth-inducingfoodlikemacroinvertebrates(HillSinarsampLodge1993)Wethusexpectedthatrustycrayfishwouldexhibitbetterphysiolog-icalconditionandhighertrophicpositionstowardtheinvasionfrontand as a result larger carapace length and higherweight (Brownetal2013)Wealsopositedthattwoadditionalmechanismscouldaffectcrayfishtraitvaluesduringrangeexpansion If larger fastergrowingandmorecompetitivecrayfisharebetterdispersersashas
beenreportedinmultipleinvasions(ChuangampPeterson2016)weexpectedtoobserveanincreaseincrayfishbodysizerelativechelalength andphysiological condition towards the invasion frontBycontrastiftrade-offsexistamongcrayfishtraitsthenselectionforhigh population growth rates and faster dispersal at the invasionleading edge could lead to unexpected changes in other trait val-ues(egdecreasedchelalength)towardstheinvasionfront(Phillipsetal2010b)
Wethenevaluatedwhetherthesephenotypicchangesinpopu-lationstowardstheinvasionfrontwerecausedbyplasticitytoenvi-ronmentalfactorsorselectionduetorangeexpansionWesoughttodisentanglethesetwosetsofprocessesbystudyingrustycray-fishsubpopulationsbothupstreamanddownstreamoftheir initiallocationofintroductionandbysimultaneouslyaccountingateachsiteforthedistancefromtheinvasioncore(reflectingtheinvasionstage at that location) gradients in environmental conditions andthe availability of food resourcesWe hypothesised that if selec-tion due to the range expansion process was driving changes inrustycrayfishtraitvaluesastheyspreadthroughouttheJDRthen
F IGURE 1emspRegionalmapoftheJohnDayRiverbasin(JDRinset)andrelativedensitiesofrustycrayfishalongthemainstemNorthForkandSouthForkoftheJDR(circlesize)withtheputativelocationofinitialintroduction(crayfishsymbol)CPUEcatchperuniteffort
TheJDRoriginatesintheBlueMountainsofnorth-easternOregon(USA) and runsundammed for457 river kmuntil its confluencewith the Columbia River just upstream from the Columbia RiverGorges(Figure1)Oneofthelargestfree-flowingriversintheUSAwithadrainageareaof21000km2theJDRisofhighconservationimportanceasitsupportsseveralfishspeciesofsignificantculturalandeconomicvalue includingendangeredspringChinooksalmonOncorhynchus tshawytschaandthreatenedsteelheadO mykiss
NativetotheOhioRiverbasinrustycrayfishisahabitatgener-alistitcaninhabitallsubstratesbutpreferscobblehabitatthrivesboth inareasofhighflowandstandingwatercanwithstandtem-peratures ranging fromclose to0degCup to35degCwith anoptimumnear 22degC and opportunistically consumes a variety of aquaticplants benthic invertebrates detritus periphyton fish eggs andsmall fish (Lorman1980MundahlampBenton1990)Maturerustycrayfishmateinlatesummerearlyfallorearlyspringandachievehighgrowthrates(BerrillampArsenault1984Lorman1980)
Rustycrayfishwas first found in the JDR in2005marking itsfirst recordedoccurrencewestoftheNorthAmericancontinentaldivide (Olden etal 2009) Evidence suggests that rusty crayfishwere first released in the late 1990s in themainstem JDR about
380kmupstreamfromitsconfluencewiththeColumbiaRivernearthe townofMountVernonOregonbya teacherandstudentsofa nearby school (Oldenetal 2009) In thec 20years since theirpresumeddateof introduction rusty crayfishhave rapidly spreadthroughouttheJDRcatchmentatratesexceeding15kmyearrais-ingconcernsthatthemainstemoftheColumbiaRivermaysoonbereached(MessagerampOlden2018)OnlythenativesignalcrayfishPacifastacus leniusculuswasknowntobepresent inthecatchmentprior to the introduction of rusty crayfish in the JDR (Larson ampOlden2011)PreviousstudiesandrecordsfromrotaryscrewtrapsoperatedbytheUSForestServiceshowthatsignalcrayfishwerewidespread throughout the JDR catchment despite low densitiesprior to the introductionof rusty crayfish (Sorenson2012DavidWoosterOregonStateUniversitypersonalcommunicationsAugust2013KeithDehartUSForestServicepersonalcommunicationsMarch2016)
22emsp|emspField data collection
Weimplementedaspatiallyextensivesurveyofrustycrayfishden-sities phenotypes and environmental conditions throughout itsinvasionrangetocapturegradientsinthesevariablesfromcoretoleading-edgepopulationsWeusedpredictionsofrustycrayfishdis-tribution inAugust 2016 from a spatially explicit individual-basedmodel (Messager amp Olden 2018) to distribute 60 sampling sitesevery5ndash10kmalongthemainstemandprimarytributariesoftheJDRencompassingtheinvasionextentofrustycrayfishSamplingwas conducted1ndash22August 2016 late enough in the summer sothat females would not be in berry young-of-the-year would belargeenoughtobesampledandalmostallmaturemaleswouldhavechangedtoareproductiveform(formI)withlargerchelaeinprepa-rationforfallmating(ButlerampStein1985Hamr1999Prins1968)
Toassesstherelativedensityofrustycrayfishacrossthecatch-mentarea-standardisedkick-seiningwasperformedinsixlocationsacross a 50-m long reach at each surveyed site One person dis-turbed 1 m2of substrateupstreamofa seinenetheldbyanotherteammember to flush crayfish downstream yielding amean andstandarddeviationofcrayfishdensityateachsiteToensurecon-sistencyinourmeasureofrelativedensityweexclusivelysampledin runs (ie rather than pools or riffles) when possible becauserunsprovidethewatervelocityanddepthneededforthissamplingmethodtobemosteffective(LarsonampOlden2016)Toavoidfalseabsencessnorkellinghand-nettingandbaitedtrapswerealsousedwhenrustycrayfishwerenotdetectedusingseining
Whererustycrayfishwerefoundthesexcarapacelength(mm)chelalength(mm)mass(g)missingchelae(yesno)andmoultingcon-dition(yesno)ofcapturedcrayfishweremeasuredateverysitewhiletwotissuesamples (abdominalwhitemuscle) from14rustycrayfishwere takenateveryothersiteRegeneratingchelae soft-shelledorvisibly smaller than the other chelawere notmeasuredWhenourstandardsamplingprotocolyieldedlt14crayfishadditionalspecimenswerecaughtbyhand-nettingsothatthesemeasurementsandtissuesamplescouldbetakenmdashalthoughtheseindividualswerenotincluded
F IGURE 2emspDensityofrustycrayfish(y-axis)asafunctionofdistancefromputativelocationofinitialintroduction(x-axis)inthemainstem(green)NorthFork(orange)andSouthFork(purple)JohnDayRiverCrayfishdensitiesareexpressedasthemean(points)and95confidenceinterval(bars)ofthecatchperuniteffort(CPUE)ThesmoothsolidlineandshadedregionrepresentthepredictedmeanCPUEand95BayesiancredibleintervalrespectivelyfromageneralisedadditivemodelVerticaldashedlinesrepresentconfluencesoftheSouthFork(at44km)andNorthFork(at87km)withthemainstemJohnDayRiver
emspensp emsp | emsp5MESSAGER And OLdEn
inourestimatesofrelativedensityWhencrayfishdensitywashighmorphologicalmeasurementswererecordedforarandomsubsampleof30ofthecrayfishthatwerecaughtbykick-seiningThefirsttissuesamplewasimmediatelystoredinnon-iodisedsaltforsubsequentδ15Nstableisotopeanalysistodeterminethetrophicpositionofrustycray-fishatthatsitemdashtheenergy-weightednumberoftrophicenergytrans-fersfromprimaryproducertocrayfish(VanderZandenampRasmussen1999) We also collected 12ndash20 mayfly nymphs (EphemeropteraHeptageniidae)inrunsandrifflesateachstudysitewherecrayfishtis-suesweresampledtocharacterisethebaselineδ15NvaluesofprimaryconsumersthroughouttheJDR(AndersonampCabana2007)Thesec-ondtissuesamplepreservedinRNAlaterregwasusedtoquantifytherelativeconcentrationofRNAandDNAinrustycrayfishcellsWhiletheamountofDNAremainsmostlyconstantincellsregardlessofcon-ditionstheamountofRNApositivelycorrelateswiththeamountofproteinsynthesis(anabolicactivity)ThereforetheratiooftheamountofRNAtothatofDNAinacellisaneffectiveeco-physiologicalindi-catorofcondition (hereafterphysiological condition) that reflects theorganismspotential investment in somatic growthandgametepro-duction (ie fertility) under a given set of environmental conditions(KoopWinkelmannBeckerHellmannampOrtmann2011)
Environmental conditions at each site were characterisedbymeasuringwater depth temperature and velocity aswell asbenthic chlorophyll a concentration of green algae and diatomsat 10 points along a transect perpendicular to the river banksThebenthic concentrationof chlorophylla is a proxyof benthicalgalbiomass (DoddsSmithampLohman2002)measuredusingaBenthotorch (Kahlert ampMcKie 2014) The biomass of macroin-vertebrateswas alsoquantified at all siteswhere crayfish tissuesamples were taken The abundance of macroinvertebrates wasassessedbytakingthree009-m2standardisedsamplesinrunsandriffleswithaD-framekicknetAllmacroinvertebratesampleswerethenwashedthrough05mmsievesandpreservedin70ethanol
23emsp|emspStable isotope analysis
Stable isotope analysiswas conducted on rusty crayfish tissuesand mayfly whole specimens to assess differences in crayfishfeedingpatterns throughout their invasiongradientAll sampleswerepreparedforisotopeanalysisusingstandardprotocolswiththeexceptionof the salt-basedpreservation a field-appropriatemethod that results inminimal anddirectionallyuniformeffectson δ13C and δ15N (Arrington ampWinemiller 2002) Prior to pro-cessingallcrayfishmuscletissuesandmayflywholebodieswererinsedwith distilledwater until the salt was dissolved Sampleswere then dried at 60degC for 24hr ground to powder and sentfornitrogenisotopeanalysistotheUniversityofCaliforniaDavisStableIsotopeFacilityThetrophicpositionofeachcrayfishatsite(S)wasestimatedaccordingto
where254istherustycrayfishdiscriminationfactororfractiona-tionfactor(Δ)representingtheabsolutedifferenceinδ15Nbetweenrusty crayfish and its diet determined in laboratory based on analgaediet(GlonLarsonampPangle2015)Weappliedasinglefrac-tionationfactortoalltrophiclinksofthefoodwebbetweenprimaryconsumersandcrayfishanddidnotaccountforfractionationdiffer-encesamongcrayfishdietsduetoalackofmorespecificreferencevalues
24emsp|emspRNADNA analysis
TheprocedurefortheextractionandquantitationofnucleicacidsinrustycrayfishtissueswasadaptedfromBerdaletRoldaacutenOlivarand Lysnes (2005) andVrede Persson andAronsen (2002) usingfluorochromesthatindiscriminatelybindtoDNAandRNAWepro-vide a brief description below but refer the reader to SupportingInformation AppendixS1 for a more detailed protocol BerdaletRoldaacutenandOlivar(2005)recommendusingthreeseparatealiquotsofeachsampletocomputethequantityofRNAandDNAincrus-taceantissuesthefirstassaymeasuresRNAafterDNAdigestionthesecondmeasuresDNAafterRNAdigestionandthethirdmeas-ures residual fluorescence after digestion of bothDNA andRNAFournucleicacidstandardcurveswithsixconcentrationseachwerethus run foreverybatchof samplesRNA+DNaseRNA+RNaseDNA+RNaseandDNA+DNaseToquantifyRNAandDNAfluo-rescence 50μl of diluted (1200) Quant-iTtrade RiboGreenreg reagentwas added to each platewell The slopes of the standard curveswerethenestimatedusinglinearregressionandthequantityofRNA(μgRNAmlassay)DNA(μgDNAmlassay)andtheirratioineachsample was calculated using the equations provided by BerdaletRoldaacutenandOlivar(2005)
25emsp|emspMacroinvertebrate biomass
Macroinvertebrate ash-free dry weight (AFDW)was estimated ateveryothersitealongthelengthoftheinvasiongradienttoreflectthepreybiomassavailableforconsumptionbyrustycrayfishoneofthemainenvironmentaldriversofcrayfishtrophicposition(Olssonetal 2008) Macroinvertebrates were sorted using a stereo mi-croscopeandseparatedfromothermaterial found inthesamplesSortedmacroinvertebrateswerethenrinsedwithdistilledwateranddriedinanovenat60degCfor48hrweighedcombustedinamufflefurnace at 550degC for 4hr (Mason LewisampWeber 1983) cooleddowntoroomtemperatureinadesiccatorfor6hrandreweighedAshmass (after combustion in furnace)was then subtracted fromdrymass(beforecombustion)toobtainAFDW
26emsp|emspData analysis
Thegoalof this studywas toassesswhetheraphenotypic shifthas occurred along the invasion gradient of rusty crayfish andwhether thisshift isbestexplainedby the rangeexpansionpro-cess or by longitudinal gradients in environmental conditions
(1)
Trophic positioncrayfishS
=2+
15NcrayfishSminus
(
sum3
mayfly=115Nmayfly S
)
∕3
254
6emsp |emsp emspensp MESSAGER And OLdEn
Environmentalconditionsandthespeedofrustycrayfishspreaddiffered among tributaries so each invasion leading edge wasanalysedseparately Intotalfour leading-edgepopulationswereanalysedonedownstreamedge in themainstemJDRand threeupstream edgesmdashin the mainstem South Fork and North ForkJDR(Figure1)
Sixtraitswereanalysedthroughouttheinvasionextentofrustycrayfish carapace length chela length weight trophic positionphysiologicalconditionandsexratio(theproportionofmalesatasite)Onlydataforcrayfishcaughtbykick-seininghand-nettingandsnorkellingwereincludedintheanalysisduetotheknownsizeandsexbiasoftrappingforlargemales(LarsonampOlden2016)Tocon-trolforthestrongrelationshipbetweenbodysizecrayfishweightandchelalengthduetoallometricgrowthresidualsfromcarapacelength-weightandcarapace length-chela lengthnon-linear regres-sionmodels developed separately for each sexwere used as re-sponsevariablesinthemodels(hereafterrelative weight and relative chela length)
A subset of the variablesmeasured at each site was selectedas potential environmental predictors of crayfish trait values theestimatednumberofdegreedays fromAugust2015 toJuly2016(degC)macroinvertebrate AFDW (mg) and chlorophyll a concentra-tion frombenthicgreenalgaeanddiatoms (μgChl-acm2)Degreedayswerecomputedbasedonwater temperatureestimated froma multiple regression model using satellite-measured daily land-surfacetemperaturecalendardaycatchmentareaandelevationaspredictorvariables (MessagerampOlden2018) In situ temperaturemeasurementswere not used in this analysis as diel temperaturevariationswereofthesameorderofmagnitudeasdifferencesbe-tween upstream and downstream sites Velocity and depth mea-surementswerenotincludedintheanalysiseitherduetotheirhighspatialvariabilityatbaseflowintheJDROnlythesitesforwhichallvariableshadbeenmeasuredwereincludedintheanalysisforatotalof18sites14sitesinthemainstemJDRtwointheSouthForkJDRandtwointheNorthForkJDR
In the South Fork andNorth Fork JDRwhere tissue samplesweretakenfromcrayfishinonlytwositesdifferencesintraitvaluesamongsiteswere testedusing two-sample t-testsanddifferencesinsexratiowereassessedwithYatesχ2testInthemainstemJDRgeneralisedadditivemodels(GAMs)weredevelopedtoanalysethedrivers of crayfish morphology physiological condition and tro-phicpositionGAMswerebuiltseparatelyfortwomaincategoriesofpredictorvariablesAfirstcategoryofmodelswasdevelopedtoaccountfortheroleoftherangeexpansionprocessindrivingphe-notypicchangesbyusingeachsitesdistancefromtheinitiallocationofrustycrayfishintroductionasthepredictorvariableThesecondmodel categorywas based on environmental variables thatmightinfluence trait valuesAdditionalmodelswerealsobuiltusingdis-tance from the initial introduction location togetherwith crayfishdensityandsex ratioaspredictorvariablesorcombiningmultipleenvironmentalvariablesThesignificanceandfitofcandidatemod-els(Akaikeinformationcriterionthep-valueofthecoefficientsandtheadjustedR2seeSupportingInformationTableS32)werethen
31emsp|emspCrayfish distribution and habitat conditions
Intotal1266crayfishwerecapturedacrossthe18sitesanalysedin thisstudyofwhich299weresampledformorphological traits259 forphysiological condition and254 for trophicpositionOursurveycombinedwithhistoricaldistributionrecordsandamodelofrustycrayfishspreadintheJDR(MessagerampOlden2018)showedthatrustycrayfishspreadatanacceleratingratesinceitsintroduc-tion and occupied at least 705km of river across the JDR catch-ment inAugust2016Bythatsummer ithadspreadnearly30kmupstreamintheNorthForkandSouthForkJDRandcolonisedthemainstem along a 250km stretch downstream of its introductionpoint(Figure1)Incontrasttoitsextensivespreaddownstreamtheupstreamspreadofrustycrayfishinthemainstemhadbeentempo-rarilyhaltedatthetimeofthesurveyduetoalow-headdam12kmupstream of the putative site of crayfish introduction Densitiesdownstream of the dam were similar to those found at the coreoftheir rangeTherefore theupstreammainsteminvasion leadingedgewasnotincludedinthisanalysisInadditionthepreciseloca-tionofthedownstreammainstemleadingedgecouldnotbedeter-minedduetolimitedaccesstotheriverthusthedownstream-mostsurveyedsitewhererustycrayfishwasfoundinthemainstemwastreatedasthedownstreamedgeoftheirrangeinthisstudy
There was a consistent decrease in rusty crayfish densitiesamongthesampledtributariesfromtheirinitiallocationofintroduc-tiontotheir invasionfrontsRustycrayfishdensities (measuredaskick-seiningcatchperuniteffortFigure2)werehighestinboththemainstem and South Fork JDR (gt30crayfishm2) 40ndash75kmdown-streamoftheinitialsiteofrustycrayfishestablishmentbutrapidlydroppedbyanorderofmagnitudebeyond60kmintheSouthForkJDRandbeyond80kminthemainstemandNorthForkJDRNativesignalcrayfishwerefoundinsympatrywithrustycrayfishinonlyafewsitesattheupstreaminvasionfrontswhererustycrayfishwerefound at lower densities (in the South Forkmainstem and othersmaller side tributaries of the JDR)Where native signal crayfishwerepresent theyoccurredatvery lowdensities (lt2crayfishm2) including in sites without rusty crayfish These findings togetherwithpastrecords (2013)ofsignalcrayfishoccurrence insympatrywithrustycrayfishatsiteswheresignalcrayfishwereabsentduringour2016surveysuggestthatsignalcrayfishisrapidlyexcludedfromsites invadedbyrustycrayfishas itspreadsacrosstheJDRcatch-mentThereforeinterspecificcompetitionwasnotconsideredasig-nificantmechanisminfluencingthetraitsinvestigatedinthisstudy
Temperature and macroinvertebrate biomass followed similarlongitudinalgradients fromupstreamtodownstreambetweenthemainstemSouthFork andNorthFork JDRwhereasbenthicbio-massofgreenalgaeanddiatomwerehighlyvariableamongtribu-taries (Supporting InformationFigureS21)Degreedays increased
emspensp emsp | emsp7MESSAGER And OLdEn
monotonically downstream while macroinvertebrate biomass de-creaseddownstreamTherewasalsoconsiderablevariabilityinmac-roinvertebrate biomass among adjacent sites including a suddenincreaseinbiomassdownstreamfromtheconfluenceofthemain-stemandtheNorthForkJDRwherelowcrayfishdensitiesprevailedGreenalgaeweresparsetoabsentinalltributariesThebiomassofdiatomsontheotherhandwashighestintheSouthForkandupper
mainstemJDR(upto45μgChl-acm2) and low in the lower main-stemandNorthForkJDRwith inconsistent longitudinalgradientsamongtributaries
32emsp|emspMorphology
Therewereconsistenttrendsinrustycrayfishmorphologyfromcore to leading-edge populations in all tributaries (Figure 4SupportingInformationAppendixS3)Therelativechelalengthof rusty crayfish in leading-edge populationswas significantlysmaller than those behind the front in all three tributaries(Mainstem GAM p=003 R2-adjusted=028 n=14 NorthFork t=217 df=29 p=004 South Fork t=303 df=42plt001 Figures3 and 4 Supporting Information TablesS31and S32) Crayfish density was also strongly and positivelyassociatedwith chela length across the JDR (MainstemGAMp=001 R2-adjusted=037 n=14 Figure4 SupportingInformation TableS32) No consistent difference was foundin mean carapace length between core and invasion frontpopulations of the JDR or betweenmale and female crayfishhowever there was a consistent decrease in carapace lengthvariance in thedirectionof the invasion inbothupstreamanddownstream dispersing populations (Figure4 SupportingInformationAppendixS3)Crayfishrelativeweightsignificantlydecreased towards the invasion front both downstream in themainstem (GAM p=004 R2-adjusted=025 n=14) and up-stream in the North Fork (W=177 p=001) and South Fork(W=328 p=001 Supporting Information FigureS41) alongwith decreasing crayfish density (Mainstem GAM p=002R2-adjusted=033 n=14 Figure4 Supporting InformationTableS32)Lastlytherewasnosignificanttrendinthepropor-tionofmalestowardsthefrontsoftheinvasiondespiteaslightincrease inmaledominance inbothupstreamanddownstreamleading edges when considering all sites where gt10 crayfishwerecaptured(SupportingInformationFigureS42)
EnvironmentalconditionswerenotstrongpredictorsofcrayfishmorphologythroughouttheirinvasiongradientDegreedaysdidnotcorrelateconsistentlyacross invasion frontswithanymorphologi-cal trait values (Figure4 Supporting Information TableS32) Forinstancewhiledecreasingupstream temperatureswerepositivelycorrelatedtorelativeweightintheSouthForkandNorthForkJDRtemperatureand relativeweightwerenegativelycorrelated in themainstemSimilarly inconsistentpatternswereobservedbetweentemperature and both relative chela length and carapace lengthMacroinvertebrate biomass (AFDW) was negatively but not sig-nificantly correlated with relative chela length and weight acrosstributariesandwasnotconsistentlyorsignificantlyassociatedwithshifts in carapace length across tributaries (Figure4 SupportingInformationTablesS31andS32)Finallywhilegreenalgaebiomasswasnotconsistentlycorrelatedwithanymorphologicaltraitvaluesdiatombiomasswaspositivelycorrelatedwithrelativechelalengthandweight throughout the JDR (Figure4 Supporting InformationTable S32)
F IGURE 3emspChangesinmeancrayfishrelativechelalength(a)trophicposition(b)andphysiologicalcondition(cRNADNAratioexpressingpotentialforsomaticgrowthandgameteproduction)alongtheinvasiongradientofrustycrayfishintheJohnDayRivercatchmentThesmoothsolidlineandshadedregionrepresentthepredictedmeantraitvalueand95Bayesiancredibleintervalrespectivelyfromageneralisedadditivemodelandasterisksdenotesignificantdifferencesinmean(ple001ple005)VerticaldashedlinesrepresenttheconfluencesoftheSouthFork(at44km)andNorthFork(at87km)withthemainstemJohnDayRiver
8emsp |emsp emspensp MESSAGER And OLdEn
33emsp|emspTrophic position
Thetrophicpositionofrustycrayfishwasconsistentlylowerforin-dividualsat invasion fronts than inpopulationscloser to thecoredespite wide variations among sites throughout the catchment
(Figures3band4SupportingInformationAppendixS3)Inthemain-stemrustycrayfishdietfirstincreaseddownstreamfromthattypi-calofasecondaryconsumeroromnivore(trophicpositionofc 3) to thatofatopcarnivore(trophicpositionofc4)andthendecreasedtowardsthefrontoftheinvasiondowntothatofaprimaryconsumer
F IGURE 4emspSummary of the relationshipsbetweenrustycrayfishtraitsandpredictorvariablesintheJohnDayRiver The direction and colour of the arrowsindicatethesignoftherelationship(egredupwardarrowsreflectpositiverelationships)betweenthepredictorvariable(columns)andthetrait(rows)foragiveninvasionleadingedge(downstreammainstemupstreamSouthForkorupstreamNorthFork)Greyarrowsshowstatisticallynon-significantrelationshipsSignificanceandaconsistentdirectionintherelationshipbetweencandidatepredictorsandtraitsamongtributariessuggestedtheprimacyofthatpredictorindrivingobserveddifferencesintraitsSeeSupportingInformationAppendixS3fordetailedstatisticalresultsFlatgreenarrowsshowvariablesforwhichtherewasnodifferenceamongsitesinthattributaryandrelationshipsdenotedbyandashwerenottestedduetoalackofhypothesisedmechanismsrelatingthevariablesdaggerAsh-freedryweight
Response variable Edge
Predictor variableDistance
from introduction
Crayfish density
Degree days
Macroinv AFDWdagger
Green algae Diatom
Relative chela length
Mainstem
South Fork
North Fork
Trophic position
Mainstem
South Fork
North Fork
Physiological Condition
(RNADNA)
Mainstem
South Fork
North Fork
Carapace length
Mainstem
South Fork
North Fork
Relative weight
Mainstem
South Fork
North Fork
Sex ratio( males)
Mainstemndash ndash ndash ndash ndash
South Forkndash ndash ndash ndash ndash
North Forkndash ndash ndash ndash ndash
Carapace length SD
Mainstemndash ndash ndash ndash
South Forkndash ndash ndash ndash
North Forkndash ndash ndash ndash
daggerAsh-free dry weight
emspensp emsp | emsp9MESSAGER And OLdEn
(trophicpositionofc2GAMp=005R2-adjusted=044n = 14 Figure3b) Therewas an equivalent drop in crayfish trophic posi-tionintheNorthForkJDRupstreamleadingedge(t=966df=22plt0001)butnoequivalentdecreaseintheSouthForkJDRleadingedgeTherewasnodifferenceintrophicpositionamongmaleandfemalecrayfishandalthoughtrophicpositionwasweaklycorrelatedwithcarapacelengthwithinsites(carapacelengthfixedeffect95CI=80times10minus3to19times10minus2trophiclevelmminlinearmixedeffectmodelwithsiteasrandomeffect)therewasnosignificantcorrela-tionbetweentrophicpositionandmeancarapacelengthacrosssitesalongthemainstemTrophicpositionwasnotsignificantlycorrelatedwithrelativechelalengthwithinsites(relativechelalengthfixedef-fect 95 CI=minus83times10minus3 to 23times10minus2 trophic levelmm in linearmixedeffectmodelwithsiteasrandomeffect)
Temperature increasing with downstream distance from theinvasionsourcewascorrelatedwithtrophicpositiononlytowardstheupstreaminvasionfrontsintheNorthForkandSouthForkJDR(Figure4Supporting InformationAppendicesS2andS3)Noneoftheotherenvironmentalvariablessignificantlycovariedwithtrophicpositioninaconsistentwayacrosstributaries(Figure4SupportingInformationAppendicesS2andS3)
34emsp|emspGrowth and condition
There was a consistent positive trend in rusty crayfish physi-ological condition (RNADNA ratio) towards invasion fronts alongwith decreasing crayfish densities (Figures3c and 4 SupportingInformationAppendixS3)Strongesttowardstheupstreamleadingedgesdespitedecreasing temperature (t-test SouthForkW=46p-value=001North Fork t=minus491df=155plt0001) the in-creaseinphysiologicalconditionwasonlymarginalinthemainstem[GAMp=019R2-adjusted=006n=14meanslope=63times10minus3 (95CI=minus27times10minus3to15times10minus2) [RNADNA]km]Thenegativecorrelation between crayfish physiological condition (RNADNAratio)andcrayfishdensityinthemainstemwasalsonon-significant(GAM p=043 R2-adjusted=minus003 n=14) Lastly environmen-tal variables (abiotic and biotic)were not consistently and signifi-cantlyassociatedwithRNADNAratioacrosstributaries(Figure4SupportingInformationAppendixS3)
4emsp |emspDISCUSSION
Thisstudyrevealedsignificanttrendsinmorphologicaltraitvaluesphysiologicalconditionandtrophicpositionofrustycrayfishfromtheirlocationofinitialintroductiontomultipleleadingedgesofinva-sionintheonlyknownpopulationofthisspeciesinwesternNorthAmericaEventhoughthesetrendswerenotconsistentlysignificantacrosstributariestheysuggestthatrustycrayfishindividualsatthevanguard of the invasion exhibited less competitive morphology(decreasedrelativeweightandchelalength)andexploitedenergeticpathwaysloweronthefoodchainyetwereinbetterphysiologicalcondition than individuals located closer to the invasion coreWe
contendthatthesephenotypicshiftsobservedinrustycrayfishareprobablydue to the rangeexpansionprocess itself rather than tonovelenvironmentalconditionsattheirrangeboundariesandthatthesetrendsmayintensifyastheinvasioncontinuestounfoldup-stream and downstream towards the main stem of the ColumbiaRiver
The observed decrease in crayfish relative chela length andweighttowardstheinvasionfrontscanbeattributedtothreemainreasonsmdashalthough further research is needed to confirm the re-spectivecontributionifanyofeachofthesemechanismsFirsttherangeexpansionofrustycrayfishmightbedrivenbytheexclusionof subdominant individuals from high-density population centresthereforeleadingtothewidespreadpresenceofcompetitivelyinfe-riorcrayfishattheinvasionleadingedge(HudinaHockampZganec2014)Inotherwordsindividualcrayfishwithlesscompetitivephe-notypesmayhavebeenforcedoutandsystematically interbredatthe invasionfront resulting in theaccumulationof relatively lightsmall-clawedindividualsattheleadingedgeInsupportofthismech-anismsignalcrayfishattheboundaryoftheirinvasionrangeacrossCroatiadisplaylowerlevelsofaggressionandoftenloseagonisticin-teractionstoindividualsfromtheinvasioncoredespitebeinginbet-ter physical condition (Hudinaetal 2015)However a significantincreaseinrelativeclawsizeawayfromsourcepopulationwasalsoobservedininvasivesignalcrayfishmalesoftheMuraRiverCroatia(Hudinaetal2012)Secondlargerchelaeandastouterbodyshapemay be associated with weaker dispersal ability and thus be se-lectedagainstthroughassociativematingofthefastestdispersersclusteredattheinvasionleadingedgeCrayfishwithshorterchelaeandmorefusiformbodyarebetterabletowithstandhighwaterve-locitiesassuggestedbymorphologicdifferencesbetweencrayfishfound in high-velocity streams compared to those in low-velocitystreams and lakes (Perry etal 2013) Becausewater velocities inexcessof03ndash05msleadtodecreasedcrayfishmovementandpo-tentially increasedenergyexpenditureincrayfish(ClarkKershnerampHolomuzki 2008Matheramp Stein 1993 Perryamp Jones 2017)individualswithshorterchelaeandmorefusiformbodiesmaythusbeabletodisperseforlongerperiodsoftheyearintheJDRwhosedischarge isunregulatedbydamsandflowregimeischaracterisedbyspringsnowmeltThirdlowrustycrayfishconspecificdensitiesat invasion front sitesmay relax the constraints imposedby com-petitioninhigh-densityareasandthusreducetherequirementforinvestment in traitsassociatedwithcompetitionShelterandfoodlimitationsarethemaindriversofagonisticinteractionsincrayfish(BergmanampMoore2003CapelliampHamilton1984)Whentheseresourcesareplentiful inpioneerpopulationsbehaviouralpheno-typesassociatedwithlargeclawsandweightaspartofanaggressionsyndrome(Hudinaetal2012)couldthereforeleadtounnecessaryenergyexpensesand reduced foraging leading to reduced fitness(SihCoteEvansFogartyampPruitt2012)Thusashiftinselectivepressuremayhave led toachange in rustycrayfish lifehistoryattheedgeoftheinvasion involvingthereallocationofenergyfromallometricgrowthofcompetitivetraitstoreproductionanddisper-saltraitsnotmeasuredhere(egwalkingleglength)(Phillipsetal
Weconjecturethatashift intheselectionregimeexperiencedbyrustycrayfishfromcoretoleading-edgeareasisthemostprob-ableexplanationforthetrends inrelativechela lengthandweightobservedinthisstudyHoweverwithoutknowledgeoftheheritabil-ityofthecrayfishtraitsexaminedinthisstudyinferenceregardingthespecificmechanisms inoperation isstill limitedTheaccelerat-ingrateofspreadofrustycrayfish intheJDRthe lowpopulationdensities observedwithin several kilometres of the upstream anddownstreaminvasionfrontsandhighphysiologicalfitnessininva-sionfrontpopulationssuggestthatapushedinvasionexcludingsub-dominantcrayfishfromhigherdensityareasisunlikelytoexplaintheobservedtraitdifferencesMoreoverthereislittletonoevidenceoftheinfluenceofchelasizeorrelativebodyweightondispersalspeed(KamranampMoore 2015) Lastly the difference in relativeweightandchelalengthbetweeninvasioncoreandfrontpopulationscouldalsobedrivenbynaturalselectioninhighcrayfishdensitycorepop-ulationsHistoricaldatafromSorenson(2012)combinedwiththisstudy shownodifference inchela length (Supporting InformationFigureS51)butasignificantincreaseinrelativeweightfrom2010to2016atthepresumedsiteofrustycrayfishintroduction(SupportingInformationFigureS52)Thechangesintraitvaluesobservedherearethuslikelytobetheresultsofacombinationofdriversincludingreducedfitnessofcompetitivephenotypesatlowcrayfishdensityselectionforhighrelativeweightinthepopulationcoreandtrade-offsbetweenthesecompetitiveattributesandother traitsassoci-atedwithhigherdispersalability
Theobserved increase in rustycrayfishanabolicactivitymea-suredasRNADNAinleading-edgepopulationsoftheJDRalthoughweak in themainstem indicates that the rangeexpansionprocesshas led to greater somatic growth andor reproductive potentialin pioneer individuals This pattern matches several documentedincreases inbodyconditiongrowthandreproductivepotential insimilarstreaminvasionsbothwithinasingleinvasiongradientandbetweennativeandnon-nativepopulationsWithintheirnon-nativerange invasion front signal crayfish in Croatia and female spiny-cheekcrayfish in theDanubebothdisplayedgreater reproductivepotentials than their counterparts in core areas with the formeralsobeinginbetterconditionandenergeticstatus(Pacircrvulescuetal2015Rebrinaetal2015)Whencomparingnativeandnon-nativepopulationsofrustycrayfishbothlakeandmesocosmexperimentsfoundthatnon-nativeindividualshavehighergrowthratesandlevelsofactivitythantheirnativecongeners(PintorampSih2009Sargentamp Lodge 2014) Nonetheless whether the observed increase inrustycrayfishphysiologicalconditiontowardstheinvasionfront isassociated with greater somatic growth rates or gamete produc-tionremainsunresolvedandwarrantsfurtherinvestigationIndeed
simultaneous increases inconditiongrowthandreproductivepo-tentialarenotuniversalbecauseselectionfordispersalabilityduringrangeexpansionmay lead tounexpected trade-offsFor instancetadpolesandjuvenilesininvasionfrontpopulationsofcanetoadsintropicalAustraliagrowupto31fasterthanthosefromlongeres-tablishedpopulations(Phillips2009)andadultsdemonstratehigherfeeding rates larger fat stores andbetter condition thanconspe-cifics in later invasion stages (Brownetal2013)However lowerreproductiverateshavealsobeendocumentedincanetoadinvasionfrontpopulations(HudsonPhillipsBrownampShine2015)
Itmightseemthathighercrayfishgrowthratestowardstheinva-sionfrontscontradicttheobservedpatternsofreducedweightandchelalengthobservedinpioneercrayfishHoweverselectionforafasterlifestylecoulddecreaseageatmaturityandshortenthelifes-panoftheseinvasionfrontcrayfishwhileselectingagainstallome-tricgrowthofcompetitivemorphologyBothcrayfishgrowth rateandfecundityaredensitydependent(GuanampWiles1999MomotampGowing1977)Thereforeitispossiblethathighgrowthandfe-cundityphenotypeshavearisenfromnaturalselectioninthec 15 generationssincetheirintroductionaspartofadispersalsyndromeassociating rapid development and high fecunditywith dispersivetraits(RonceampClobert2012Stevensetal2013)
Rustycrayfishattheleadingedgesoftheirdistributionallimitsappeartobefeedinglowerinthefoodwebwhencomparedtocon-specifics locatedbehind the invasion frontThispattern stands incontradictionwithmostpreviousstudiesofstreaminvasionsRoundgobiesattheedgeoftheirexpandingrangeconsumemoreoftheirfavouredpreytypethanincentralpopulations(RabyGutowskyampFox2010)andhavehigherδ15Nsignaturesthanthepreviousyearfront(Brandneretal2013)Invasionfrontbloodyredmysidshrimp(Hemimysis anomala)werenotmoreselectiveintheirpreyconsump-tionbutshowedgreaterabilitytolocateandcapturezooplanktonprey than those shrimp in corepopulations (Iacarella etal 2015)ForcrayfishinvasionstrophicnicheshiftshaveonlybeenassessedatthebiogeographicalscaleandoffermixedinsightsInagreementwithourfindingsnon-nativepopulationsofrustycrayfishandvirilecrayfish(Faxonius virilis)appearedtoshowgreaterratesofalgaecon-sumption (despite constant macroinvertebrate prey consumption)thandidnativepopulationsinlaboratoryassays(Glonetal2018)By contrast an intercontinental stable isotope analysis revealedtrophicnicheconservatisminsignalcrayfishbetweenitsnativeandnon-native range (LarsonOldenampUsio 2010) Trophic flexibilityhasbeenshowntobespecies-dependenteveninsympatricnativecrayfishspecies (JohnstonRobsonampFairweather2011)andmaythus not be a consistent characteristic among invasive omnivoreseitherItisunlikelythatcannibalismawidespreadphenomenonincrayfishpopulations(GuanampWiles1998) ledtotheobservedin-creaseintrophicpositioninareaswithhighdensitiesofcrayfishasconspecificdensitywasnotcorrelatedtotrophicpositionintheJDR(Figure4SupportingInformationAppendixS3)Lastlyitisunlikelythatnon-crayfishpredatorsandcompetitorscouldhavedriventhisdownwardshiftinthetrophicpositionofrustycrayfishasthisshiftwasobservedacrossboththedownstream(increasingfishdensity)
Rustycrayfishhada lower trophicpositionevenwhenmacro-invertebrateprey availability increased towards the invasion frontintheNorthForkJDRThispatterncontrastedwithpastevidenceof a positive relationship between macroinvertebrate availabilityand crayfish trophic position (Olsson etal 2008) and greater as-similation efficiencies of invertebrates than other food items bycrayfish (WhitledgeampRabeni 1997)However the lackof signifi-cantdecreaseintrophicpositiontowardstheinvasionfront intheSouth Fork JDR could be due to a counter-effect from increasingmacroinvertebrate biomass upstream Consumption of macroin-vertebrateshasbeen linkedto increases inweightgainandmeta-bolicrates(BondarBottriellZeronampRichardson2005Hilletal1993 McFeeters Xenopoulos Spooner Wagner amp Frost 2011)Nevertheless in these same studies juvenile signal crayfish in anatural settingdisproportionatelyconsumedfoodtypes thatweretheoppositeofthoseshowntobeofmostnutritionalvaluetothem(Bondar etal 2005) and rusty crayfishmortalitywashigheron adietbasedoninvertebratethanoneonperiphytonordetritus(Hilletal 1993) This suggests that high growth might be associatedwith greater physiological stress due tomore frequentmoultingandhigherforagingcostsinnaturalsettingsThuswehypothesisethatenergyintakeandlong-termfitnessofrustycrayfishassociatedwithperiphytonanddetritusconsumptionmaybehigherthanwithmacroinvertebratedietsdespitetheir lowerdigestionefficiencyoftheseresources
Trade-offs can also arise between increased dispersal rates atrangemarginsand the functional responseof thenon-nativecon-sumer due to the high cost of dispersal (Fronhofer amp Altermatt2015)Giventheircurrentrateofspread(c20kmyeardownstreamfrom2010to2016)intheJDR(MessagerampOlden2018)andawin-dowofactivityof8ndash9months(basedonwatertemperaturesinthemainstem)rustycrayfishwouldhavetoachieveanetdownstreamspreadrateof80mdayonaveragewithoutconsideringtimeded-icatedtomatingandjuvenileparentalcareWespeculatethatthispacecouldrestricttheamountoftimeavailableforactivelypreyingoninvertebratesandcouldselectforthosecrayfishbestabletoef-ficientlyfeedandgrowonabundantandaccessiblebasalresourcesIthasalsobeenhypothesisedforstreamfishesthatthosenon-nativespeciesthatcansustaingrowthandreproductiononlow-qualityre-sourcesshouldbebestabletobecomeestablished(GidoampFranssen2007) Incrayfishabroader trophicniche thatexpandedtowardslower trophic levelsmayhaveaffordedcompetitiveadvantages totheintroducedsignalcrayfishoverthenativenoblecrayfishAstacus astacus inSwedishstreams (OlssonStenrothNystromampGraneli2009) Therefore our findings that rusty crayfish at the invasionfrontactmostlyasprimaryconsumerswhileachievinggreaterphys-iologicalconditionmightreflectanincreaseinfeedingefficiencyonbasal resources as a by-product of greater dispersal ability devel-opedthroughtheirrangeexpansionintheJDR
a crucial first step towards developing spatially explicit strategiestocontrol this invasion If thedocumentedphenotypicshifts fromcore to invasion front populations are indeed associatedwith theaccelerating rateof spreadof rusty crayfish then targeting thoseindividualsattheinvasionleadingedgeforremoval(egbytrapping)mightconstraintheaccumulationofdispersivephenotypesintheseareasAccountingforthesephenotypicshiftsinmechanisticmodelsofinvasivespread(egMessagerampOlden2018)couldalsoprovideuswithavirtual laboratorytotesttheeffectivenessofalternativecontrolstrategiesincontainingthespreadofriverineinvaderssuchasrustycrayfish
Our results suggest that low conspecific densities and spatialsortinginleading-edgepopulationsledtoashift inthephenotypeofrustycrayfishtowards lowercompetitiveabilityhigher intrinsicgrowthandorreproductionandgreaterforagingefficiencyonbasalresourcesastheyspreadupstreamanddownstreamintheJDROurstudydesignenabledustolinkmorphologicalandfunctionaltraitstobetterexploretheconsequencesofthisrangeexpansiononinvadedecosystemsWeexpectthatthediminishedcompetitiveabilityob-servedinthevanguardofthisrustycrayfishinvasionmightleadtoreducedfitnessoftheinvasionfrontphenotypesoncedensities innewlycolonisedareas limit theavailabilityofshelterand intensifycompetition formatesThe long-termevolutionary implicationsofthesephenotypicshiftsmightthusbelimited(PerkinsBoettigerampPhillips2016)Howeverthetrophicshiftobservedininvasionfrontpopulationscouldalsoallowrustycrayfishtoreachhigherdensitiesintheseareasastheymightexploitresourcesmorebroadlyandeffi-cientlyundercompetitiveconditionsTheevolutionaryforcesatplayinthisinvasionhaveprobablyinteractedwithlongitudinalgradientsinenvironmentalconditionsinwaysanalogoustothoseexperiencedbyspeciesduringtheirmigrationtowardscoolerareasunderclimatechangeIntegratingthestudyofmorphologicalandfunctionaltraitswith spatial variation in environmental conditions thus provides arobustwaytoassesswhethercontemporaryevolutionisalteringthephenotypeandecosystemimpactsofspeciesastheirrangeexpandsthroughthelandscape
Inconclusionthisstudyaddsevidenceinsupportofphenotypicchangesexpectedinnon-nativeorganismsexposedtochangingse-lectionpressuresas they invadenewenvironmentsDisentanglingthe causes of these changes whether related to environmentalfactorsorselectionduetorangeexpansionremainsan importantareaofinvestigationasweseektobetterunderstandtheecologicalimpactsofinvasivespeciesandhownativespecieswillrespondtoshiftingenvironmentalconditionsinthefuture
ACKNOWLEDG MENTS
WethankJeffAdamsEricLarsonDavidWoosterStephenBollensandKeithSorensonforprovidinghistoricaldataforrustycrayfishthe staff at theGrantCountyAssessorsoffice and the JohnDayFossilBedsNationalMonument for their help accessing the riverParticular appreciation goes to all the landowners throughout theJohnDayRiverbasin foraccess to their landandsupport for this
12emsp |emsp emspensp MESSAGER And OLdEn
projectWearegratefultoJacobCrunkforhisinestimablehelpwithfieldworkandEthenWhattamforhishelpprocessingmacroinver-tebratesamplesFromtheUniversityofWashingtonwethanktheMolecularEcologyResearchLaboratory(MERLab)andmorespecifi-callyIsadoraJimenez-HidalgoandNatalieLowelltheOldenlabaswellasJoshuaLawlerThomasQuinnandPatrickTobinThemanu-scriptwasimprovedbythecommentsfromtwoanonymousreview-ersFundingsupportwasprovidedbytheJohnNCobbScholarshipin Fisheries the Simpson Award from the Society for FreshwaterScienceandtheCrustaceanSocietyfellowshipinGraduateStudiesawarded to MLM and the University of Washington H MasonKeelerEndowedProfessorshipawardtoJDO
Mathis L Messager httpsorcidorg0000-0002-3051-8068
Julian D Olden httpsorcidorg0000-0003-2143-1187
R E FE R E N C E S
AndersonCampCabanaG (2007)Estimatingthetrophicpositionofaquatic consumers in river food webs using stable nitrogen iso-topes Journal of the North American Benthological Society 26(2)273ndash285 httpsdoiorg1018990887-3593(2007)26[273ettpoa]20co2
Arrington D A ampWinemiller K O (2002) Preservation effects onstable isotope analysis of fishmuscleTransactions of the American Fisheries Society131(2)337ndash342httpsdoiorg1015771548-8659(2002)131lt0337peosiagt20co2
Berdalet E Roldaacuten C ampOlivarM P (2005) Quantifying RNA andDNAinplanktonicorganismswithSYBRGreenIIandnucleasesPartBQuantification in natural samplesScientia Marina69(1) 17ndash30httpsdoiorg103989scimar200569n117
BerdaletERoldaacutenCOlivarMPampLysnesK (2005)QuantifyingRNAandDNAinplanktonicorganismswithSYBRGreenIIandnu-cleases Part A Optimisation of the assay Scientia Marina 69(1)1ndash16httpsdoiorg103989scimar200569n11
Bobeldyk A M amp Lamberti G A (2010) Stream food web re-sponses to a large omnivorous invader Orconectes rusticus (Decapoda Cambaridae) Crustaceana 83(6) 641ndash657 httpsdoiorg101163001121610x491031
BondarCABottriellKZeronKampRichardsonJS(2005)Doestro-phicpositionof theomnivoroussignalcrayfish (Pacifastacus lenius-culus) inastreamfoodwebvarywith lifehistorystageordensityCanadian Journal of Fisheries and Aquatic Sciences62(11)2632ndash2639httpsdoiorg101139f05-167
BrandnerJCerwenkaAFSchliewenUKampGeistJ(2013)BiggerisbetterCharacteristicsofroundgobiesforminganinvasionfrontinthe Danube River PLoS ONE8(9)e73036httpsdoiorg101371journalpone0073036
BrownGPKelehearCampShineR (2013)Theearly toadgets theworm Cane toads at an invasion front benefit from higher preyavailability Journal of Animal Ecology 82(4) 854ndash862 httpsdoiorg1011111365-265612048
Burton O J Phillips B L amp Travis J M J (2010) Trade-offs and the evolution of life-histories during range ex-pansion Ecology Letters 13(10) 1210ndash1220 httpsdoiorg101111j1461-0248201001505x
Capelli G M amp Hamilton P A (1984) Effects of food shelter andtimeof dayon aggressive activity in the crayfishOrconectes rusti-cus(Girard)Journal of Crustacean Biology4(2)252ndash260httpsdoiorg1011631937240x84x00363
Caplat P Cheptou P O Diez J Guisan A Larson B MMacDougall A S hellip Zhang R (2013) Movement impacts andmanagement of plant distributions in response to climate changeInsights from invasions Oikos 122(9) 1265ndash1274 httpsdoiorg101111j1600-0706201300430x
Chuang A amp Peterson C R (2016) Expanding population edgesTheories traits and trade-offsGlobal Change Biology22(2) 494ndash512httpsdoiorg101111gcb13107
ClarkJMKershnerMWampHolomuzkiJR(2008)Grainsizeandsorting effects on size-dependent responses by lotic crayfish tohigh flows Hydrobiologia 610 55ndash66 httpsdoiorg101007s10750-008-9422-0
CrandallKAampDeGraveS (2017)Anupdatedclassificationofthefreshwater crayfishes (Decapoda Astacidea) of the world with acompletespecieslistJournal of Crustacean Biology37(5)615ndash653httpsdoiorg101093jcbiolrux070
DavidsonAMJennionsMampNicotraAB(2011)Doinvasivespe-cies show higher phenotypic plasticity than native species and ifso is it adaptiveAmeta-analysisEcology Letters14(4) 419ndash431httpsdoiorg101111j1461-0248201101596x
DoddsWK Smith VH amp Lohman K (2002)Nitrogen and phos-phorusrelationshipstobenthicalgalbiomassintemperatestreamsCanadian Journal of Fisheries and Aquatic Sciences 59(5) 865ndash874httpsdoiorg101139f02-063
Fronhofer E A amp Altermatt F (2015) Eco-evolutionary feedbacksduring experimental range expansions Nature Communications 66844httpsdoiorg101038ncomms7844
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
emspensp emsp | emsp3MESSAGER And OLdEn
Our objective was two-foldWe first assessed whether rustycrayfish individuals displayed phenotypic differences progressingfromestablishedcorepopulationsnear the initial locationof theirintroduction to recently colonised invasion frontsWeused a riv-erscapesurveytoanalyserustycrayfishpopulationstructuremor-phology physiological condition and trophic position across itsrangeinthemainstemoftheJDRanditsmaintributariesWehy-pothesisedthatphenotypicchangesoccurredacrossrustycrayfishgenerations as they dispersed from their location of introductiontotheirpresent invasionfronts in theJDRWeexpectedthat lowconspecificdensitiesinnewlyinvadedriversectionswouldleadtoincreasedaccesstoresourcesandrelativeconsumptionofgrowth-inducingfoodlikemacroinvertebrates(HillSinarsampLodge1993)Wethusexpectedthatrustycrayfishwouldexhibitbetterphysiolog-icalconditionandhighertrophicpositionstowardtheinvasionfrontand as a result larger carapace length and higherweight (Brownetal2013)Wealsopositedthattwoadditionalmechanismscouldaffectcrayfishtraitvaluesduringrangeexpansion If larger fastergrowingandmorecompetitivecrayfisharebetterdispersersashas
beenreportedinmultipleinvasions(ChuangampPeterson2016)weexpectedtoobserveanincreaseincrayfishbodysizerelativechelalength andphysiological condition towards the invasion frontBycontrastiftrade-offsexistamongcrayfishtraitsthenselectionforhigh population growth rates and faster dispersal at the invasionleading edge could lead to unexpected changes in other trait val-ues(egdecreasedchelalength)towardstheinvasionfront(Phillipsetal2010b)
Wethenevaluatedwhetherthesephenotypicchangesinpopu-lationstowardstheinvasionfrontwerecausedbyplasticitytoenvi-ronmentalfactorsorselectionduetorangeexpansionWesoughttodisentanglethesetwosetsofprocessesbystudyingrustycray-fishsubpopulationsbothupstreamanddownstreamoftheir initiallocationofintroductionandbysimultaneouslyaccountingateachsiteforthedistancefromtheinvasioncore(reflectingtheinvasionstage at that location) gradients in environmental conditions andthe availability of food resourcesWe hypothesised that if selec-tion due to the range expansion process was driving changes inrustycrayfishtraitvaluesastheyspreadthroughouttheJDRthen
F IGURE 1emspRegionalmapoftheJohnDayRiverbasin(JDRinset)andrelativedensitiesofrustycrayfishalongthemainstemNorthForkandSouthForkoftheJDR(circlesize)withtheputativelocationofinitialintroduction(crayfishsymbol)CPUEcatchperuniteffort
TheJDRoriginatesintheBlueMountainsofnorth-easternOregon(USA) and runsundammed for457 river kmuntil its confluencewith the Columbia River just upstream from the Columbia RiverGorges(Figure1)Oneofthelargestfree-flowingriversintheUSAwithadrainageareaof21000km2theJDRisofhighconservationimportanceasitsupportsseveralfishspeciesofsignificantculturalandeconomicvalue includingendangeredspringChinooksalmonOncorhynchus tshawytschaandthreatenedsteelheadO mykiss
NativetotheOhioRiverbasinrustycrayfishisahabitatgener-alistitcaninhabitallsubstratesbutpreferscobblehabitatthrivesboth inareasofhighflowandstandingwatercanwithstandtem-peratures ranging fromclose to0degCup to35degCwith anoptimumnear 22degC and opportunistically consumes a variety of aquaticplants benthic invertebrates detritus periphyton fish eggs andsmall fish (Lorman1980MundahlampBenton1990)Maturerustycrayfishmateinlatesummerearlyfallorearlyspringandachievehighgrowthrates(BerrillampArsenault1984Lorman1980)
Rustycrayfishwas first found in the JDR in2005marking itsfirst recordedoccurrencewestoftheNorthAmericancontinentaldivide (Olden etal 2009) Evidence suggests that rusty crayfishwere first released in the late 1990s in themainstem JDR about
380kmupstreamfromitsconfluencewiththeColumbiaRivernearthe townofMountVernonOregonbya teacherandstudentsofa nearby school (Oldenetal 2009) In thec 20years since theirpresumeddateof introduction rusty crayfishhave rapidly spreadthroughouttheJDRcatchmentatratesexceeding15kmyearrais-ingconcernsthatthemainstemoftheColumbiaRivermaysoonbereached(MessagerampOlden2018)OnlythenativesignalcrayfishPacifastacus leniusculuswasknowntobepresent inthecatchmentprior to the introduction of rusty crayfish in the JDR (Larson ampOlden2011)PreviousstudiesandrecordsfromrotaryscrewtrapsoperatedbytheUSForestServiceshowthatsignalcrayfishwerewidespread throughout the JDR catchment despite low densitiesprior to the introductionof rusty crayfish (Sorenson2012DavidWoosterOregonStateUniversitypersonalcommunicationsAugust2013KeithDehartUSForestServicepersonalcommunicationsMarch2016)
22emsp|emspField data collection
Weimplementedaspatiallyextensivesurveyofrustycrayfishden-sities phenotypes and environmental conditions throughout itsinvasionrangetocapturegradientsinthesevariablesfromcoretoleading-edgepopulationsWeusedpredictionsofrustycrayfishdis-tribution inAugust 2016 from a spatially explicit individual-basedmodel (Messager amp Olden 2018) to distribute 60 sampling sitesevery5ndash10kmalongthemainstemandprimarytributariesoftheJDRencompassingtheinvasionextentofrustycrayfishSamplingwas conducted1ndash22August 2016 late enough in the summer sothat females would not be in berry young-of-the-year would belargeenoughtobesampledandalmostallmaturemaleswouldhavechangedtoareproductiveform(formI)withlargerchelaeinprepa-rationforfallmating(ButlerampStein1985Hamr1999Prins1968)
Toassesstherelativedensityofrustycrayfishacrossthecatch-mentarea-standardisedkick-seiningwasperformedinsixlocationsacross a 50-m long reach at each surveyed site One person dis-turbed 1 m2of substrateupstreamofa seinenetheldbyanotherteammember to flush crayfish downstream yielding amean andstandarddeviationofcrayfishdensityateachsiteToensurecon-sistencyinourmeasureofrelativedensityweexclusivelysampledin runs (ie rather than pools or riffles) when possible becauserunsprovidethewatervelocityanddepthneededforthissamplingmethodtobemosteffective(LarsonampOlden2016)Toavoidfalseabsencessnorkellinghand-nettingandbaitedtrapswerealsousedwhenrustycrayfishwerenotdetectedusingseining
Whererustycrayfishwerefoundthesexcarapacelength(mm)chelalength(mm)mass(g)missingchelae(yesno)andmoultingcon-dition(yesno)ofcapturedcrayfishweremeasuredateverysitewhiletwotissuesamples (abdominalwhitemuscle) from14rustycrayfishwere takenateveryothersiteRegeneratingchelae soft-shelledorvisibly smaller than the other chelawere notmeasuredWhenourstandardsamplingprotocolyieldedlt14crayfishadditionalspecimenswerecaughtbyhand-nettingsothatthesemeasurementsandtissuesamplescouldbetakenmdashalthoughtheseindividualswerenotincluded
F IGURE 2emspDensityofrustycrayfish(y-axis)asafunctionofdistancefromputativelocationofinitialintroduction(x-axis)inthemainstem(green)NorthFork(orange)andSouthFork(purple)JohnDayRiverCrayfishdensitiesareexpressedasthemean(points)and95confidenceinterval(bars)ofthecatchperuniteffort(CPUE)ThesmoothsolidlineandshadedregionrepresentthepredictedmeanCPUEand95BayesiancredibleintervalrespectivelyfromageneralisedadditivemodelVerticaldashedlinesrepresentconfluencesoftheSouthFork(at44km)andNorthFork(at87km)withthemainstemJohnDayRiver
emspensp emsp | emsp5MESSAGER And OLdEn
inourestimatesofrelativedensityWhencrayfishdensitywashighmorphologicalmeasurementswererecordedforarandomsubsampleof30ofthecrayfishthatwerecaughtbykick-seiningThefirsttissuesamplewasimmediatelystoredinnon-iodisedsaltforsubsequentδ15Nstableisotopeanalysistodeterminethetrophicpositionofrustycray-fishatthatsitemdashtheenergy-weightednumberoftrophicenergytrans-fersfromprimaryproducertocrayfish(VanderZandenampRasmussen1999) We also collected 12ndash20 mayfly nymphs (EphemeropteraHeptageniidae)inrunsandrifflesateachstudysitewherecrayfishtis-suesweresampledtocharacterisethebaselineδ15NvaluesofprimaryconsumersthroughouttheJDR(AndersonampCabana2007)Thesec-ondtissuesamplepreservedinRNAlaterregwasusedtoquantifytherelativeconcentrationofRNAandDNAinrustycrayfishcellsWhiletheamountofDNAremainsmostlyconstantincellsregardlessofcon-ditionstheamountofRNApositivelycorrelateswiththeamountofproteinsynthesis(anabolicactivity)ThereforetheratiooftheamountofRNAtothatofDNAinacellisaneffectiveeco-physiologicalindi-catorofcondition (hereafterphysiological condition) that reflects theorganismspotential investment in somatic growthandgametepro-duction (ie fertility) under a given set of environmental conditions(KoopWinkelmannBeckerHellmannampOrtmann2011)
Environmental conditions at each site were characterisedbymeasuringwater depth temperature and velocity aswell asbenthic chlorophyll a concentration of green algae and diatomsat 10 points along a transect perpendicular to the river banksThebenthic concentrationof chlorophylla is a proxyof benthicalgalbiomass (DoddsSmithampLohman2002)measuredusingaBenthotorch (Kahlert ampMcKie 2014) The biomass of macroin-vertebrateswas alsoquantified at all siteswhere crayfish tissuesamples were taken The abundance of macroinvertebrates wasassessedbytakingthree009-m2standardisedsamplesinrunsandriffleswithaD-framekicknetAllmacroinvertebratesampleswerethenwashedthrough05mmsievesandpreservedin70ethanol
23emsp|emspStable isotope analysis
Stable isotope analysiswas conducted on rusty crayfish tissuesand mayfly whole specimens to assess differences in crayfishfeedingpatterns throughout their invasiongradientAll sampleswerepreparedforisotopeanalysisusingstandardprotocolswiththeexceptionof the salt-basedpreservation a field-appropriatemethod that results inminimal anddirectionallyuniformeffectson δ13C and δ15N (Arrington ampWinemiller 2002) Prior to pro-cessingallcrayfishmuscletissuesandmayflywholebodieswererinsedwith distilledwater until the salt was dissolved Sampleswere then dried at 60degC for 24hr ground to powder and sentfornitrogenisotopeanalysistotheUniversityofCaliforniaDavisStableIsotopeFacilityThetrophicpositionofeachcrayfishatsite(S)wasestimatedaccordingto
where254istherustycrayfishdiscriminationfactororfractiona-tionfactor(Δ)representingtheabsolutedifferenceinδ15Nbetweenrusty crayfish and its diet determined in laboratory based on analgaediet(GlonLarsonampPangle2015)Weappliedasinglefrac-tionationfactortoalltrophiclinksofthefoodwebbetweenprimaryconsumersandcrayfishanddidnotaccountforfractionationdiffer-encesamongcrayfishdietsduetoalackofmorespecificreferencevalues
24emsp|emspRNADNA analysis
TheprocedurefortheextractionandquantitationofnucleicacidsinrustycrayfishtissueswasadaptedfromBerdaletRoldaacutenOlivarand Lysnes (2005) andVrede Persson andAronsen (2002) usingfluorochromesthatindiscriminatelybindtoDNAandRNAWepro-vide a brief description below but refer the reader to SupportingInformation AppendixS1 for a more detailed protocol BerdaletRoldaacutenandOlivar(2005)recommendusingthreeseparatealiquotsofeachsampletocomputethequantityofRNAandDNAincrus-taceantissuesthefirstassaymeasuresRNAafterDNAdigestionthesecondmeasuresDNAafterRNAdigestionandthethirdmeas-ures residual fluorescence after digestion of bothDNA andRNAFournucleicacidstandardcurveswithsixconcentrationseachwerethus run foreverybatchof samplesRNA+DNaseRNA+RNaseDNA+RNaseandDNA+DNaseToquantifyRNAandDNAfluo-rescence 50μl of diluted (1200) Quant-iTtrade RiboGreenreg reagentwas added to each platewell The slopes of the standard curveswerethenestimatedusinglinearregressionandthequantityofRNA(μgRNAmlassay)DNA(μgDNAmlassay)andtheirratioineachsample was calculated using the equations provided by BerdaletRoldaacutenandOlivar(2005)
25emsp|emspMacroinvertebrate biomass
Macroinvertebrate ash-free dry weight (AFDW)was estimated ateveryothersitealongthelengthoftheinvasiongradienttoreflectthepreybiomassavailableforconsumptionbyrustycrayfishoneofthemainenvironmentaldriversofcrayfishtrophicposition(Olssonetal 2008) Macroinvertebrates were sorted using a stereo mi-croscopeandseparatedfromothermaterial found inthesamplesSortedmacroinvertebrateswerethenrinsedwithdistilledwateranddriedinanovenat60degCfor48hrweighedcombustedinamufflefurnace at 550degC for 4hr (Mason LewisampWeber 1983) cooleddowntoroomtemperatureinadesiccatorfor6hrandreweighedAshmass (after combustion in furnace)was then subtracted fromdrymass(beforecombustion)toobtainAFDW
26emsp|emspData analysis
Thegoalof this studywas toassesswhetheraphenotypic shifthas occurred along the invasion gradient of rusty crayfish andwhether thisshift isbestexplainedby the rangeexpansionpro-cess or by longitudinal gradients in environmental conditions
(1)
Trophic positioncrayfishS
=2+
15NcrayfishSminus
(
sum3
mayfly=115Nmayfly S
)
∕3
254
6emsp |emsp emspensp MESSAGER And OLdEn
Environmentalconditionsandthespeedofrustycrayfishspreaddiffered among tributaries so each invasion leading edge wasanalysedseparately Intotalfour leading-edgepopulationswereanalysedonedownstreamedge in themainstemJDRand threeupstream edgesmdashin the mainstem South Fork and North ForkJDR(Figure1)
Sixtraitswereanalysedthroughouttheinvasionextentofrustycrayfish carapace length chela length weight trophic positionphysiologicalconditionandsexratio(theproportionofmalesatasite)Onlydataforcrayfishcaughtbykick-seininghand-nettingandsnorkellingwereincludedintheanalysisduetotheknownsizeandsexbiasoftrappingforlargemales(LarsonampOlden2016)Tocon-trolforthestrongrelationshipbetweenbodysizecrayfishweightandchelalengthduetoallometricgrowthresidualsfromcarapacelength-weightandcarapace length-chela lengthnon-linear regres-sionmodels developed separately for each sexwere used as re-sponsevariablesinthemodels(hereafterrelative weight and relative chela length)
A subset of the variablesmeasured at each site was selectedas potential environmental predictors of crayfish trait values theestimatednumberofdegreedays fromAugust2015 toJuly2016(degC)macroinvertebrate AFDW (mg) and chlorophyll a concentra-tion frombenthicgreenalgaeanddiatoms (μgChl-acm2)Degreedayswerecomputedbasedonwater temperatureestimated froma multiple regression model using satellite-measured daily land-surfacetemperaturecalendardaycatchmentareaandelevationaspredictorvariables (MessagerampOlden2018) In situ temperaturemeasurementswere not used in this analysis as diel temperaturevariationswereofthesameorderofmagnitudeasdifferencesbe-tween upstream and downstream sites Velocity and depth mea-surementswerenotincludedintheanalysiseitherduetotheirhighspatialvariabilityatbaseflowintheJDROnlythesitesforwhichallvariableshadbeenmeasuredwereincludedintheanalysisforatotalof18sites14sitesinthemainstemJDRtwointheSouthForkJDRandtwointheNorthForkJDR
In the South Fork andNorth Fork JDRwhere tissue samplesweretakenfromcrayfishinonlytwositesdifferencesintraitvaluesamongsiteswere testedusing two-sample t-testsanddifferencesinsexratiowereassessedwithYatesχ2testInthemainstemJDRgeneralisedadditivemodels(GAMs)weredevelopedtoanalysethedrivers of crayfish morphology physiological condition and tro-phicpositionGAMswerebuiltseparatelyfortwomaincategoriesofpredictorvariablesAfirstcategoryofmodelswasdevelopedtoaccountfortheroleoftherangeexpansionprocessindrivingphe-notypicchangesbyusingeachsitesdistancefromtheinitiallocationofrustycrayfishintroductionasthepredictorvariableThesecondmodel categorywas based on environmental variables thatmightinfluence trait valuesAdditionalmodelswerealsobuiltusingdis-tance from the initial introduction location togetherwith crayfishdensityandsex ratioaspredictorvariablesorcombiningmultipleenvironmentalvariablesThesignificanceandfitofcandidatemod-els(Akaikeinformationcriterionthep-valueofthecoefficientsandtheadjustedR2seeSupportingInformationTableS32)werethen
31emsp|emspCrayfish distribution and habitat conditions
Intotal1266crayfishwerecapturedacrossthe18sitesanalysedin thisstudyofwhich299weresampledformorphological traits259 forphysiological condition and254 for trophicpositionOursurveycombinedwithhistoricaldistributionrecordsandamodelofrustycrayfishspreadintheJDR(MessagerampOlden2018)showedthatrustycrayfishspreadatanacceleratingratesinceitsintroduc-tion and occupied at least 705km of river across the JDR catch-ment inAugust2016Bythatsummer ithadspreadnearly30kmupstreamintheNorthForkandSouthForkJDRandcolonisedthemainstem along a 250km stretch downstream of its introductionpoint(Figure1)Incontrasttoitsextensivespreaddownstreamtheupstreamspreadofrustycrayfishinthemainstemhadbeentempo-rarilyhaltedatthetimeofthesurveyduetoalow-headdam12kmupstream of the putative site of crayfish introduction Densitiesdownstream of the dam were similar to those found at the coreoftheir rangeTherefore theupstreammainsteminvasion leadingedgewasnotincludedinthisanalysisInadditionthepreciseloca-tionofthedownstreammainstemleadingedgecouldnotbedeter-minedduetolimitedaccesstotheriverthusthedownstream-mostsurveyedsitewhererustycrayfishwasfoundinthemainstemwastreatedasthedownstreamedgeoftheirrangeinthisstudy
There was a consistent decrease in rusty crayfish densitiesamongthesampledtributariesfromtheirinitiallocationofintroduc-tiontotheir invasionfrontsRustycrayfishdensities (measuredaskick-seiningcatchperuniteffortFigure2)werehighestinboththemainstem and South Fork JDR (gt30crayfishm2) 40ndash75kmdown-streamoftheinitialsiteofrustycrayfishestablishmentbutrapidlydroppedbyanorderofmagnitudebeyond60kmintheSouthForkJDRandbeyond80kminthemainstemandNorthForkJDRNativesignalcrayfishwerefoundinsympatrywithrustycrayfishinonlyafewsitesattheupstreaminvasionfrontswhererustycrayfishwerefound at lower densities (in the South Forkmainstem and othersmaller side tributaries of the JDR)Where native signal crayfishwerepresent theyoccurredatvery lowdensities (lt2crayfishm2) including in sites without rusty crayfish These findings togetherwithpastrecords (2013)ofsignalcrayfishoccurrence insympatrywithrustycrayfishatsiteswheresignalcrayfishwereabsentduringour2016surveysuggestthatsignalcrayfishisrapidlyexcludedfromsites invadedbyrustycrayfishas itspreadsacrosstheJDRcatch-mentThereforeinterspecificcompetitionwasnotconsideredasig-nificantmechanisminfluencingthetraitsinvestigatedinthisstudy
Temperature and macroinvertebrate biomass followed similarlongitudinalgradients fromupstreamtodownstreambetweenthemainstemSouthFork andNorthFork JDRwhereasbenthicbio-massofgreenalgaeanddiatomwerehighlyvariableamongtribu-taries (Supporting InformationFigureS21)Degreedays increased
emspensp emsp | emsp7MESSAGER And OLdEn
monotonically downstream while macroinvertebrate biomass de-creaseddownstreamTherewasalsoconsiderablevariabilityinmac-roinvertebrate biomass among adjacent sites including a suddenincreaseinbiomassdownstreamfromtheconfluenceofthemain-stemandtheNorthForkJDRwherelowcrayfishdensitiesprevailedGreenalgaeweresparsetoabsentinalltributariesThebiomassofdiatomsontheotherhandwashighestintheSouthForkandupper
mainstemJDR(upto45μgChl-acm2) and low in the lower main-stemandNorthForkJDRwith inconsistent longitudinalgradientsamongtributaries
32emsp|emspMorphology
Therewereconsistenttrendsinrustycrayfishmorphologyfromcore to leading-edge populations in all tributaries (Figure 4SupportingInformationAppendixS3)Therelativechelalengthof rusty crayfish in leading-edge populationswas significantlysmaller than those behind the front in all three tributaries(Mainstem GAM p=003 R2-adjusted=028 n=14 NorthFork t=217 df=29 p=004 South Fork t=303 df=42plt001 Figures3 and 4 Supporting Information TablesS31and S32) Crayfish density was also strongly and positivelyassociatedwith chela length across the JDR (MainstemGAMp=001 R2-adjusted=037 n=14 Figure4 SupportingInformation TableS32) No consistent difference was foundin mean carapace length between core and invasion frontpopulations of the JDR or betweenmale and female crayfishhowever there was a consistent decrease in carapace lengthvariance in thedirectionof the invasion inbothupstreamanddownstream dispersing populations (Figure4 SupportingInformationAppendixS3)Crayfishrelativeweightsignificantlydecreased towards the invasion front both downstream in themainstem (GAM p=004 R2-adjusted=025 n=14) and up-stream in the North Fork (W=177 p=001) and South Fork(W=328 p=001 Supporting Information FigureS41) alongwith decreasing crayfish density (Mainstem GAM p=002R2-adjusted=033 n=14 Figure4 Supporting InformationTableS32)Lastlytherewasnosignificanttrendinthepropor-tionofmalestowardsthefrontsoftheinvasiondespiteaslightincrease inmaledominance inbothupstreamanddownstreamleading edges when considering all sites where gt10 crayfishwerecaptured(SupportingInformationFigureS42)
EnvironmentalconditionswerenotstrongpredictorsofcrayfishmorphologythroughouttheirinvasiongradientDegreedaysdidnotcorrelateconsistentlyacross invasion frontswithanymorphologi-cal trait values (Figure4 Supporting Information TableS32) Forinstancewhiledecreasingupstream temperatureswerepositivelycorrelatedtorelativeweightintheSouthForkandNorthForkJDRtemperatureand relativeweightwerenegativelycorrelated in themainstemSimilarly inconsistentpatternswereobservedbetweentemperature and both relative chela length and carapace lengthMacroinvertebrate biomass (AFDW) was negatively but not sig-nificantly correlated with relative chela length and weight acrosstributariesandwasnotconsistentlyorsignificantlyassociatedwithshifts in carapace length across tributaries (Figure4 SupportingInformationTablesS31andS32)Finallywhilegreenalgaebiomasswasnotconsistentlycorrelatedwithanymorphologicaltraitvaluesdiatombiomasswaspositivelycorrelatedwithrelativechelalengthandweight throughout the JDR (Figure4 Supporting InformationTable S32)
F IGURE 3emspChangesinmeancrayfishrelativechelalength(a)trophicposition(b)andphysiologicalcondition(cRNADNAratioexpressingpotentialforsomaticgrowthandgameteproduction)alongtheinvasiongradientofrustycrayfishintheJohnDayRivercatchmentThesmoothsolidlineandshadedregionrepresentthepredictedmeantraitvalueand95Bayesiancredibleintervalrespectivelyfromageneralisedadditivemodelandasterisksdenotesignificantdifferencesinmean(ple001ple005)VerticaldashedlinesrepresenttheconfluencesoftheSouthFork(at44km)andNorthFork(at87km)withthemainstemJohnDayRiver
8emsp |emsp emspensp MESSAGER And OLdEn
33emsp|emspTrophic position
Thetrophicpositionofrustycrayfishwasconsistentlylowerforin-dividualsat invasion fronts than inpopulationscloser to thecoredespite wide variations among sites throughout the catchment
(Figures3band4SupportingInformationAppendixS3)Inthemain-stemrustycrayfishdietfirstincreaseddownstreamfromthattypi-calofasecondaryconsumeroromnivore(trophicpositionofc 3) to thatofatopcarnivore(trophicpositionofc4)andthendecreasedtowardsthefrontoftheinvasiondowntothatofaprimaryconsumer
F IGURE 4emspSummary of the relationshipsbetweenrustycrayfishtraitsandpredictorvariablesintheJohnDayRiver The direction and colour of the arrowsindicatethesignoftherelationship(egredupwardarrowsreflectpositiverelationships)betweenthepredictorvariable(columns)andthetrait(rows)foragiveninvasionleadingedge(downstreammainstemupstreamSouthForkorupstreamNorthFork)Greyarrowsshowstatisticallynon-significantrelationshipsSignificanceandaconsistentdirectionintherelationshipbetweencandidatepredictorsandtraitsamongtributariessuggestedtheprimacyofthatpredictorindrivingobserveddifferencesintraitsSeeSupportingInformationAppendixS3fordetailedstatisticalresultsFlatgreenarrowsshowvariablesforwhichtherewasnodifferenceamongsitesinthattributaryandrelationshipsdenotedbyandashwerenottestedduetoalackofhypothesisedmechanismsrelatingthevariablesdaggerAsh-freedryweight
Response variable Edge
Predictor variableDistance
from introduction
Crayfish density
Degree days
Macroinv AFDWdagger
Green algae Diatom
Relative chela length
Mainstem
South Fork
North Fork
Trophic position
Mainstem
South Fork
North Fork
Physiological Condition
(RNADNA)
Mainstem
South Fork
North Fork
Carapace length
Mainstem
South Fork
North Fork
Relative weight
Mainstem
South Fork
North Fork
Sex ratio( males)
Mainstemndash ndash ndash ndash ndash
South Forkndash ndash ndash ndash ndash
North Forkndash ndash ndash ndash ndash
Carapace length SD
Mainstemndash ndash ndash ndash
South Forkndash ndash ndash ndash
North Forkndash ndash ndash ndash
daggerAsh-free dry weight
emspensp emsp | emsp9MESSAGER And OLdEn
(trophicpositionofc2GAMp=005R2-adjusted=044n = 14 Figure3b) Therewas an equivalent drop in crayfish trophic posi-tionintheNorthForkJDRupstreamleadingedge(t=966df=22plt0001)butnoequivalentdecreaseintheSouthForkJDRleadingedgeTherewasnodifferenceintrophicpositionamongmaleandfemalecrayfishandalthoughtrophicpositionwasweaklycorrelatedwithcarapacelengthwithinsites(carapacelengthfixedeffect95CI=80times10minus3to19times10minus2trophiclevelmminlinearmixedeffectmodelwithsiteasrandomeffect)therewasnosignificantcorrela-tionbetweentrophicpositionandmeancarapacelengthacrosssitesalongthemainstemTrophicpositionwasnotsignificantlycorrelatedwithrelativechelalengthwithinsites(relativechelalengthfixedef-fect 95 CI=minus83times10minus3 to 23times10minus2 trophic levelmm in linearmixedeffectmodelwithsiteasrandomeffect)
Temperature increasing with downstream distance from theinvasionsourcewascorrelatedwithtrophicpositiononlytowardstheupstreaminvasionfrontsintheNorthForkandSouthForkJDR(Figure4Supporting InformationAppendicesS2andS3)Noneoftheotherenvironmentalvariablessignificantlycovariedwithtrophicpositioninaconsistentwayacrosstributaries(Figure4SupportingInformationAppendicesS2andS3)
34emsp|emspGrowth and condition
There was a consistent positive trend in rusty crayfish physi-ological condition (RNADNA ratio) towards invasion fronts alongwith decreasing crayfish densities (Figures3c and 4 SupportingInformationAppendixS3)Strongesttowardstheupstreamleadingedgesdespitedecreasing temperature (t-test SouthForkW=46p-value=001North Fork t=minus491df=155plt0001) the in-creaseinphysiologicalconditionwasonlymarginalinthemainstem[GAMp=019R2-adjusted=006n=14meanslope=63times10minus3 (95CI=minus27times10minus3to15times10minus2) [RNADNA]km]Thenegativecorrelation between crayfish physiological condition (RNADNAratio)andcrayfishdensityinthemainstemwasalsonon-significant(GAM p=043 R2-adjusted=minus003 n=14) Lastly environmen-tal variables (abiotic and biotic)were not consistently and signifi-cantlyassociatedwithRNADNAratioacrosstributaries(Figure4SupportingInformationAppendixS3)
4emsp |emspDISCUSSION
Thisstudyrevealedsignificanttrendsinmorphologicaltraitvaluesphysiologicalconditionandtrophicpositionofrustycrayfishfromtheirlocationofinitialintroductiontomultipleleadingedgesofinva-sionintheonlyknownpopulationofthisspeciesinwesternNorthAmericaEventhoughthesetrendswerenotconsistentlysignificantacrosstributariestheysuggestthatrustycrayfishindividualsatthevanguard of the invasion exhibited less competitive morphology(decreasedrelativeweightandchelalength)andexploitedenergeticpathwaysloweronthefoodchainyetwereinbetterphysiologicalcondition than individuals located closer to the invasion coreWe
contendthatthesephenotypicshiftsobservedinrustycrayfishareprobablydue to the rangeexpansionprocess itself rather than tonovelenvironmentalconditionsattheirrangeboundariesandthatthesetrendsmayintensifyastheinvasioncontinuestounfoldup-stream and downstream towards the main stem of the ColumbiaRiver
The observed decrease in crayfish relative chela length andweighttowardstheinvasionfrontscanbeattributedtothreemainreasonsmdashalthough further research is needed to confirm the re-spectivecontributionifanyofeachofthesemechanismsFirsttherangeexpansionofrustycrayfishmightbedrivenbytheexclusionof subdominant individuals from high-density population centresthereforeleadingtothewidespreadpresenceofcompetitivelyinfe-riorcrayfishattheinvasionleadingedge(HudinaHockampZganec2014)Inotherwordsindividualcrayfishwithlesscompetitivephe-notypesmayhavebeenforcedoutandsystematically interbredatthe invasionfront resulting in theaccumulationof relatively lightsmall-clawedindividualsattheleadingedgeInsupportofthismech-anismsignalcrayfishattheboundaryoftheirinvasionrangeacrossCroatiadisplaylowerlevelsofaggressionandoftenloseagonisticin-teractionstoindividualsfromtheinvasioncoredespitebeinginbet-ter physical condition (Hudinaetal 2015)However a significantincreaseinrelativeclawsizeawayfromsourcepopulationwasalsoobservedininvasivesignalcrayfishmalesoftheMuraRiverCroatia(Hudinaetal2012)Secondlargerchelaeandastouterbodyshapemay be associated with weaker dispersal ability and thus be se-lectedagainstthroughassociativematingofthefastestdispersersclusteredattheinvasionleadingedgeCrayfishwithshorterchelaeandmorefusiformbodyarebetterabletowithstandhighwaterve-locitiesassuggestedbymorphologicdifferencesbetweencrayfishfound in high-velocity streams compared to those in low-velocitystreams and lakes (Perry etal 2013) Becausewater velocities inexcessof03ndash05msleadtodecreasedcrayfishmovementandpo-tentially increasedenergyexpenditureincrayfish(ClarkKershnerampHolomuzki 2008Matheramp Stein 1993 Perryamp Jones 2017)individualswithshorterchelaeandmorefusiformbodiesmaythusbeabletodisperseforlongerperiodsoftheyearintheJDRwhosedischarge isunregulatedbydamsandflowregimeischaracterisedbyspringsnowmeltThirdlowrustycrayfishconspecificdensitiesat invasion front sitesmay relax the constraints imposedby com-petitioninhigh-densityareasandthusreducetherequirementforinvestment in traitsassociatedwithcompetitionShelterandfoodlimitationsarethemaindriversofagonisticinteractionsincrayfish(BergmanampMoore2003CapelliampHamilton1984)Whentheseresourcesareplentiful inpioneerpopulationsbehaviouralpheno-typesassociatedwithlargeclawsandweightaspartofanaggressionsyndrome(Hudinaetal2012)couldthereforeleadtounnecessaryenergyexpensesand reduced foraging leading to reduced fitness(SihCoteEvansFogartyampPruitt2012)Thusashiftinselectivepressuremayhave led toachange in rustycrayfish lifehistoryattheedgeoftheinvasion involvingthereallocationofenergyfromallometricgrowthofcompetitivetraitstoreproductionanddisper-saltraitsnotmeasuredhere(egwalkingleglength)(Phillipsetal
Weconjecturethatashift intheselectionregimeexperiencedbyrustycrayfishfromcoretoleading-edgeareasisthemostprob-ableexplanationforthetrends inrelativechela lengthandweightobservedinthisstudyHoweverwithoutknowledgeoftheheritabil-ityofthecrayfishtraitsexaminedinthisstudyinferenceregardingthespecificmechanisms inoperation isstill limitedTheaccelerat-ingrateofspreadofrustycrayfish intheJDRthe lowpopulationdensities observedwithin several kilometres of the upstream anddownstreaminvasionfrontsandhighphysiologicalfitnessininva-sionfrontpopulationssuggestthatapushedinvasionexcludingsub-dominantcrayfishfromhigherdensityareasisunlikelytoexplaintheobservedtraitdifferencesMoreoverthereislittletonoevidenceoftheinfluenceofchelasizeorrelativebodyweightondispersalspeed(KamranampMoore 2015) Lastly the difference in relativeweightandchelalengthbetweeninvasioncoreandfrontpopulationscouldalsobedrivenbynaturalselectioninhighcrayfishdensitycorepop-ulationsHistoricaldatafromSorenson(2012)combinedwiththisstudy shownodifference inchela length (Supporting InformationFigureS51)butasignificantincreaseinrelativeweightfrom2010to2016atthepresumedsiteofrustycrayfishintroduction(SupportingInformationFigureS52)Thechangesintraitvaluesobservedherearethuslikelytobetheresultsofacombinationofdriversincludingreducedfitnessofcompetitivephenotypesatlowcrayfishdensityselectionforhighrelativeweightinthepopulationcoreandtrade-offsbetweenthesecompetitiveattributesandother traitsassoci-atedwithhigherdispersalability
Theobserved increase in rustycrayfishanabolicactivitymea-suredasRNADNAinleading-edgepopulationsoftheJDRalthoughweak in themainstem indicates that the rangeexpansionprocesshas led to greater somatic growth andor reproductive potentialin pioneer individuals This pattern matches several documentedincreases inbodyconditiongrowthandreproductivepotential insimilarstreaminvasionsbothwithinasingleinvasiongradientandbetweennativeandnon-nativepopulationsWithintheirnon-nativerange invasion front signal crayfish in Croatia and female spiny-cheekcrayfish in theDanubebothdisplayedgreater reproductivepotentials than their counterparts in core areas with the formeralsobeinginbetterconditionandenergeticstatus(Pacircrvulescuetal2015Rebrinaetal2015)Whencomparingnativeandnon-nativepopulationsofrustycrayfishbothlakeandmesocosmexperimentsfoundthatnon-nativeindividualshavehighergrowthratesandlevelsofactivitythantheirnativecongeners(PintorampSih2009Sargentamp Lodge 2014) Nonetheless whether the observed increase inrustycrayfishphysiologicalconditiontowardstheinvasionfront isassociated with greater somatic growth rates or gamete produc-tionremainsunresolvedandwarrantsfurtherinvestigationIndeed
simultaneous increases inconditiongrowthandreproductivepo-tentialarenotuniversalbecauseselectionfordispersalabilityduringrangeexpansionmay lead tounexpected trade-offsFor instancetadpolesandjuvenilesininvasionfrontpopulationsofcanetoadsintropicalAustraliagrowupto31fasterthanthosefromlongeres-tablishedpopulations(Phillips2009)andadultsdemonstratehigherfeeding rates larger fat stores andbetter condition thanconspe-cifics in later invasion stages (Brownetal2013)However lowerreproductiverateshavealsobeendocumentedincanetoadinvasionfrontpopulations(HudsonPhillipsBrownampShine2015)
Itmightseemthathighercrayfishgrowthratestowardstheinva-sionfrontscontradicttheobservedpatternsofreducedweightandchelalengthobservedinpioneercrayfishHoweverselectionforafasterlifestylecoulddecreaseageatmaturityandshortenthelifes-panoftheseinvasionfrontcrayfishwhileselectingagainstallome-tricgrowthofcompetitivemorphologyBothcrayfishgrowth rateandfecundityaredensitydependent(GuanampWiles1999MomotampGowing1977)Thereforeitispossiblethathighgrowthandfe-cundityphenotypeshavearisenfromnaturalselectioninthec 15 generationssincetheirintroductionaspartofadispersalsyndromeassociating rapid development and high fecunditywith dispersivetraits(RonceampClobert2012Stevensetal2013)
Rustycrayfishattheleadingedgesoftheirdistributionallimitsappeartobefeedinglowerinthefoodwebwhencomparedtocon-specifics locatedbehind the invasion frontThispattern stands incontradictionwithmostpreviousstudiesofstreaminvasionsRoundgobiesattheedgeoftheirexpandingrangeconsumemoreoftheirfavouredpreytypethanincentralpopulations(RabyGutowskyampFox2010)andhavehigherδ15Nsignaturesthanthepreviousyearfront(Brandneretal2013)Invasionfrontbloodyredmysidshrimp(Hemimysis anomala)werenotmoreselectiveintheirpreyconsump-tionbutshowedgreaterabilitytolocateandcapturezooplanktonprey than those shrimp in corepopulations (Iacarella etal 2015)ForcrayfishinvasionstrophicnicheshiftshaveonlybeenassessedatthebiogeographicalscaleandoffermixedinsightsInagreementwithourfindingsnon-nativepopulationsofrustycrayfishandvirilecrayfish(Faxonius virilis)appearedtoshowgreaterratesofalgaecon-sumption (despite constant macroinvertebrate prey consumption)thandidnativepopulationsinlaboratoryassays(Glonetal2018)By contrast an intercontinental stable isotope analysis revealedtrophicnicheconservatisminsignalcrayfishbetweenitsnativeandnon-native range (LarsonOldenampUsio 2010) Trophic flexibilityhasbeenshowntobespecies-dependenteveninsympatricnativecrayfishspecies (JohnstonRobsonampFairweather2011)andmaythus not be a consistent characteristic among invasive omnivoreseitherItisunlikelythatcannibalismawidespreadphenomenonincrayfishpopulations(GuanampWiles1998) ledtotheobservedin-creaseintrophicpositioninareaswithhighdensitiesofcrayfishasconspecificdensitywasnotcorrelatedtotrophicpositionintheJDR(Figure4SupportingInformationAppendixS3)Lastlyitisunlikelythatnon-crayfishpredatorsandcompetitorscouldhavedriventhisdownwardshiftinthetrophicpositionofrustycrayfishasthisshiftwasobservedacrossboththedownstream(increasingfishdensity)
Rustycrayfishhada lower trophicpositionevenwhenmacro-invertebrateprey availability increased towards the invasion frontintheNorthForkJDRThispatterncontrastedwithpastevidenceof a positive relationship between macroinvertebrate availabilityand crayfish trophic position (Olsson etal 2008) and greater as-similation efficiencies of invertebrates than other food items bycrayfish (WhitledgeampRabeni 1997)However the lackof signifi-cantdecreaseintrophicpositiontowardstheinvasionfront intheSouth Fork JDR could be due to a counter-effect from increasingmacroinvertebrate biomass upstream Consumption of macroin-vertebrateshasbeen linkedto increases inweightgainandmeta-bolicrates(BondarBottriellZeronampRichardson2005Hilletal1993 McFeeters Xenopoulos Spooner Wagner amp Frost 2011)Nevertheless in these same studies juvenile signal crayfish in anatural settingdisproportionatelyconsumedfoodtypes thatweretheoppositeofthoseshowntobeofmostnutritionalvaluetothem(Bondar etal 2005) and rusty crayfishmortalitywashigheron adietbasedoninvertebratethanoneonperiphytonordetritus(Hilletal 1993) This suggests that high growth might be associatedwith greater physiological stress due tomore frequentmoultingandhigherforagingcostsinnaturalsettingsThuswehypothesisethatenergyintakeandlong-termfitnessofrustycrayfishassociatedwithperiphytonanddetritusconsumptionmaybehigherthanwithmacroinvertebratedietsdespitetheir lowerdigestionefficiencyoftheseresources
Trade-offs can also arise between increased dispersal rates atrangemarginsand the functional responseof thenon-nativecon-sumer due to the high cost of dispersal (Fronhofer amp Altermatt2015)Giventheircurrentrateofspread(c20kmyeardownstreamfrom2010to2016)intheJDR(MessagerampOlden2018)andawin-dowofactivityof8ndash9months(basedonwatertemperaturesinthemainstem)rustycrayfishwouldhavetoachieveanetdownstreamspreadrateof80mdayonaveragewithoutconsideringtimeded-icatedtomatingandjuvenileparentalcareWespeculatethatthispacecouldrestricttheamountoftimeavailableforactivelypreyingoninvertebratesandcouldselectforthosecrayfishbestabletoef-ficientlyfeedandgrowonabundantandaccessiblebasalresourcesIthasalsobeenhypothesisedforstreamfishesthatthosenon-nativespeciesthatcansustaingrowthandreproductiononlow-qualityre-sourcesshouldbebestabletobecomeestablished(GidoampFranssen2007) Incrayfishabroader trophicniche thatexpandedtowardslower trophic levelsmayhaveaffordedcompetitiveadvantages totheintroducedsignalcrayfishoverthenativenoblecrayfishAstacus astacus inSwedishstreams (OlssonStenrothNystromampGraneli2009) Therefore our findings that rusty crayfish at the invasionfrontactmostlyasprimaryconsumerswhileachievinggreaterphys-iologicalconditionmightreflectanincreaseinfeedingefficiencyonbasal resources as a by-product of greater dispersal ability devel-opedthroughtheirrangeexpansionintheJDR
a crucial first step towards developing spatially explicit strategiestocontrol this invasion If thedocumentedphenotypicshifts fromcore to invasion front populations are indeed associatedwith theaccelerating rateof spreadof rusty crayfish then targeting thoseindividualsattheinvasionleadingedgeforremoval(egbytrapping)mightconstraintheaccumulationofdispersivephenotypesintheseareasAccountingforthesephenotypicshiftsinmechanisticmodelsofinvasivespread(egMessagerampOlden2018)couldalsoprovideuswithavirtual laboratorytotesttheeffectivenessofalternativecontrolstrategiesincontainingthespreadofriverineinvaderssuchasrustycrayfish
Our results suggest that low conspecific densities and spatialsortinginleading-edgepopulationsledtoashift inthephenotypeofrustycrayfishtowards lowercompetitiveabilityhigher intrinsicgrowthandorreproductionandgreaterforagingefficiencyonbasalresourcesastheyspreadupstreamanddownstreamintheJDROurstudydesignenabledustolinkmorphologicalandfunctionaltraitstobetterexploretheconsequencesofthisrangeexpansiononinvadedecosystemsWeexpectthatthediminishedcompetitiveabilityob-servedinthevanguardofthisrustycrayfishinvasionmightleadtoreducedfitnessoftheinvasionfrontphenotypesoncedensities innewlycolonisedareas limit theavailabilityofshelterand intensifycompetition formatesThe long-termevolutionary implicationsofthesephenotypicshiftsmightthusbelimited(PerkinsBoettigerampPhillips2016)Howeverthetrophicshiftobservedininvasionfrontpopulationscouldalsoallowrustycrayfishtoreachhigherdensitiesintheseareasastheymightexploitresourcesmorebroadlyandeffi-cientlyundercompetitiveconditionsTheevolutionaryforcesatplayinthisinvasionhaveprobablyinteractedwithlongitudinalgradientsinenvironmentalconditionsinwaysanalogoustothoseexperiencedbyspeciesduringtheirmigrationtowardscoolerareasunderclimatechangeIntegratingthestudyofmorphologicalandfunctionaltraitswith spatial variation in environmental conditions thus provides arobustwaytoassesswhethercontemporaryevolutionisalteringthephenotypeandecosystemimpactsofspeciesastheirrangeexpandsthroughthelandscape
Inconclusionthisstudyaddsevidenceinsupportofphenotypicchangesexpectedinnon-nativeorganismsexposedtochangingse-lectionpressuresas they invadenewenvironmentsDisentanglingthe causes of these changes whether related to environmentalfactorsorselectionduetorangeexpansionremainsan importantareaofinvestigationasweseektobetterunderstandtheecologicalimpactsofinvasivespeciesandhownativespecieswillrespondtoshiftingenvironmentalconditionsinthefuture
ACKNOWLEDG MENTS
WethankJeffAdamsEricLarsonDavidWoosterStephenBollensandKeithSorensonforprovidinghistoricaldataforrustycrayfishthe staff at theGrantCountyAssessorsoffice and the JohnDayFossilBedsNationalMonument for their help accessing the riverParticular appreciation goes to all the landowners throughout theJohnDayRiverbasin foraccess to their landandsupport for this
12emsp |emsp emspensp MESSAGER And OLdEn
projectWearegratefultoJacobCrunkforhisinestimablehelpwithfieldworkandEthenWhattamforhishelpprocessingmacroinver-tebratesamplesFromtheUniversityofWashingtonwethanktheMolecularEcologyResearchLaboratory(MERLab)andmorespecifi-callyIsadoraJimenez-HidalgoandNatalieLowelltheOldenlabaswellasJoshuaLawlerThomasQuinnandPatrickTobinThemanu-scriptwasimprovedbythecommentsfromtwoanonymousreview-ersFundingsupportwasprovidedbytheJohnNCobbScholarshipin Fisheries the Simpson Award from the Society for FreshwaterScienceandtheCrustaceanSocietyfellowshipinGraduateStudiesawarded to MLM and the University of Washington H MasonKeelerEndowedProfessorshipawardtoJDO
Mathis L Messager httpsorcidorg0000-0002-3051-8068
Julian D Olden httpsorcidorg0000-0003-2143-1187
R E FE R E N C E S
AndersonCampCabanaG (2007)Estimatingthetrophicpositionofaquatic consumers in river food webs using stable nitrogen iso-topes Journal of the North American Benthological Society 26(2)273ndash285 httpsdoiorg1018990887-3593(2007)26[273ettpoa]20co2
Arrington D A ampWinemiller K O (2002) Preservation effects onstable isotope analysis of fishmuscleTransactions of the American Fisheries Society131(2)337ndash342httpsdoiorg1015771548-8659(2002)131lt0337peosiagt20co2
Berdalet E Roldaacuten C ampOlivarM P (2005) Quantifying RNA andDNAinplanktonicorganismswithSYBRGreenIIandnucleasesPartBQuantification in natural samplesScientia Marina69(1) 17ndash30httpsdoiorg103989scimar200569n117
BerdaletERoldaacutenCOlivarMPampLysnesK (2005)QuantifyingRNAandDNAinplanktonicorganismswithSYBRGreenIIandnu-cleases Part A Optimisation of the assay Scientia Marina 69(1)1ndash16httpsdoiorg103989scimar200569n11
Bobeldyk A M amp Lamberti G A (2010) Stream food web re-sponses to a large omnivorous invader Orconectes rusticus (Decapoda Cambaridae) Crustaceana 83(6) 641ndash657 httpsdoiorg101163001121610x491031
BondarCABottriellKZeronKampRichardsonJS(2005)Doestro-phicpositionof theomnivoroussignalcrayfish (Pacifastacus lenius-culus) inastreamfoodwebvarywith lifehistorystageordensityCanadian Journal of Fisheries and Aquatic Sciences62(11)2632ndash2639httpsdoiorg101139f05-167
BrandnerJCerwenkaAFSchliewenUKampGeistJ(2013)BiggerisbetterCharacteristicsofroundgobiesforminganinvasionfrontinthe Danube River PLoS ONE8(9)e73036httpsdoiorg101371journalpone0073036
BrownGPKelehearCampShineR (2013)Theearly toadgets theworm Cane toads at an invasion front benefit from higher preyavailability Journal of Animal Ecology 82(4) 854ndash862 httpsdoiorg1011111365-265612048
Burton O J Phillips B L amp Travis J M J (2010) Trade-offs and the evolution of life-histories during range ex-pansion Ecology Letters 13(10) 1210ndash1220 httpsdoiorg101111j1461-0248201001505x
Capelli G M amp Hamilton P A (1984) Effects of food shelter andtimeof dayon aggressive activity in the crayfishOrconectes rusti-cus(Girard)Journal of Crustacean Biology4(2)252ndash260httpsdoiorg1011631937240x84x00363
Caplat P Cheptou P O Diez J Guisan A Larson B MMacDougall A S hellip Zhang R (2013) Movement impacts andmanagement of plant distributions in response to climate changeInsights from invasions Oikos 122(9) 1265ndash1274 httpsdoiorg101111j1600-0706201300430x
Chuang A amp Peterson C R (2016) Expanding population edgesTheories traits and trade-offsGlobal Change Biology22(2) 494ndash512httpsdoiorg101111gcb13107
ClarkJMKershnerMWampHolomuzkiJR(2008)Grainsizeandsorting effects on size-dependent responses by lotic crayfish tohigh flows Hydrobiologia 610 55ndash66 httpsdoiorg101007s10750-008-9422-0
CrandallKAampDeGraveS (2017)Anupdatedclassificationofthefreshwater crayfishes (Decapoda Astacidea) of the world with acompletespecieslistJournal of Crustacean Biology37(5)615ndash653httpsdoiorg101093jcbiolrux070
DavidsonAMJennionsMampNicotraAB(2011)Doinvasivespe-cies show higher phenotypic plasticity than native species and ifso is it adaptiveAmeta-analysisEcology Letters14(4) 419ndash431httpsdoiorg101111j1461-0248201101596x
DoddsWK Smith VH amp Lohman K (2002)Nitrogen and phos-phorusrelationshipstobenthicalgalbiomassintemperatestreamsCanadian Journal of Fisheries and Aquatic Sciences 59(5) 865ndash874httpsdoiorg101139f02-063
Fronhofer E A amp Altermatt F (2015) Eco-evolutionary feedbacksduring experimental range expansions Nature Communications 66844httpsdoiorg101038ncomms7844
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
TheJDRoriginatesintheBlueMountainsofnorth-easternOregon(USA) and runsundammed for457 river kmuntil its confluencewith the Columbia River just upstream from the Columbia RiverGorges(Figure1)Oneofthelargestfree-flowingriversintheUSAwithadrainageareaof21000km2theJDRisofhighconservationimportanceasitsupportsseveralfishspeciesofsignificantculturalandeconomicvalue includingendangeredspringChinooksalmonOncorhynchus tshawytschaandthreatenedsteelheadO mykiss
NativetotheOhioRiverbasinrustycrayfishisahabitatgener-alistitcaninhabitallsubstratesbutpreferscobblehabitatthrivesboth inareasofhighflowandstandingwatercanwithstandtem-peratures ranging fromclose to0degCup to35degCwith anoptimumnear 22degC and opportunistically consumes a variety of aquaticplants benthic invertebrates detritus periphyton fish eggs andsmall fish (Lorman1980MundahlampBenton1990)Maturerustycrayfishmateinlatesummerearlyfallorearlyspringandachievehighgrowthrates(BerrillampArsenault1984Lorman1980)
Rustycrayfishwas first found in the JDR in2005marking itsfirst recordedoccurrencewestoftheNorthAmericancontinentaldivide (Olden etal 2009) Evidence suggests that rusty crayfishwere first released in the late 1990s in themainstem JDR about
380kmupstreamfromitsconfluencewiththeColumbiaRivernearthe townofMountVernonOregonbya teacherandstudentsofa nearby school (Oldenetal 2009) In thec 20years since theirpresumeddateof introduction rusty crayfishhave rapidly spreadthroughouttheJDRcatchmentatratesexceeding15kmyearrais-ingconcernsthatthemainstemoftheColumbiaRivermaysoonbereached(MessagerampOlden2018)OnlythenativesignalcrayfishPacifastacus leniusculuswasknowntobepresent inthecatchmentprior to the introduction of rusty crayfish in the JDR (Larson ampOlden2011)PreviousstudiesandrecordsfromrotaryscrewtrapsoperatedbytheUSForestServiceshowthatsignalcrayfishwerewidespread throughout the JDR catchment despite low densitiesprior to the introductionof rusty crayfish (Sorenson2012DavidWoosterOregonStateUniversitypersonalcommunicationsAugust2013KeithDehartUSForestServicepersonalcommunicationsMarch2016)
22emsp|emspField data collection
Weimplementedaspatiallyextensivesurveyofrustycrayfishden-sities phenotypes and environmental conditions throughout itsinvasionrangetocapturegradientsinthesevariablesfromcoretoleading-edgepopulationsWeusedpredictionsofrustycrayfishdis-tribution inAugust 2016 from a spatially explicit individual-basedmodel (Messager amp Olden 2018) to distribute 60 sampling sitesevery5ndash10kmalongthemainstemandprimarytributariesoftheJDRencompassingtheinvasionextentofrustycrayfishSamplingwas conducted1ndash22August 2016 late enough in the summer sothat females would not be in berry young-of-the-year would belargeenoughtobesampledandalmostallmaturemaleswouldhavechangedtoareproductiveform(formI)withlargerchelaeinprepa-rationforfallmating(ButlerampStein1985Hamr1999Prins1968)
Toassesstherelativedensityofrustycrayfishacrossthecatch-mentarea-standardisedkick-seiningwasperformedinsixlocationsacross a 50-m long reach at each surveyed site One person dis-turbed 1 m2of substrateupstreamofa seinenetheldbyanotherteammember to flush crayfish downstream yielding amean andstandarddeviationofcrayfishdensityateachsiteToensurecon-sistencyinourmeasureofrelativedensityweexclusivelysampledin runs (ie rather than pools or riffles) when possible becauserunsprovidethewatervelocityanddepthneededforthissamplingmethodtobemosteffective(LarsonampOlden2016)Toavoidfalseabsencessnorkellinghand-nettingandbaitedtrapswerealsousedwhenrustycrayfishwerenotdetectedusingseining
Whererustycrayfishwerefoundthesexcarapacelength(mm)chelalength(mm)mass(g)missingchelae(yesno)andmoultingcon-dition(yesno)ofcapturedcrayfishweremeasuredateverysitewhiletwotissuesamples (abdominalwhitemuscle) from14rustycrayfishwere takenateveryothersiteRegeneratingchelae soft-shelledorvisibly smaller than the other chelawere notmeasuredWhenourstandardsamplingprotocolyieldedlt14crayfishadditionalspecimenswerecaughtbyhand-nettingsothatthesemeasurementsandtissuesamplescouldbetakenmdashalthoughtheseindividualswerenotincluded
F IGURE 2emspDensityofrustycrayfish(y-axis)asafunctionofdistancefromputativelocationofinitialintroduction(x-axis)inthemainstem(green)NorthFork(orange)andSouthFork(purple)JohnDayRiverCrayfishdensitiesareexpressedasthemean(points)and95confidenceinterval(bars)ofthecatchperuniteffort(CPUE)ThesmoothsolidlineandshadedregionrepresentthepredictedmeanCPUEand95BayesiancredibleintervalrespectivelyfromageneralisedadditivemodelVerticaldashedlinesrepresentconfluencesoftheSouthFork(at44km)andNorthFork(at87km)withthemainstemJohnDayRiver
emspensp emsp | emsp5MESSAGER And OLdEn
inourestimatesofrelativedensityWhencrayfishdensitywashighmorphologicalmeasurementswererecordedforarandomsubsampleof30ofthecrayfishthatwerecaughtbykick-seiningThefirsttissuesamplewasimmediatelystoredinnon-iodisedsaltforsubsequentδ15Nstableisotopeanalysistodeterminethetrophicpositionofrustycray-fishatthatsitemdashtheenergy-weightednumberoftrophicenergytrans-fersfromprimaryproducertocrayfish(VanderZandenampRasmussen1999) We also collected 12ndash20 mayfly nymphs (EphemeropteraHeptageniidae)inrunsandrifflesateachstudysitewherecrayfishtis-suesweresampledtocharacterisethebaselineδ15NvaluesofprimaryconsumersthroughouttheJDR(AndersonampCabana2007)Thesec-ondtissuesamplepreservedinRNAlaterregwasusedtoquantifytherelativeconcentrationofRNAandDNAinrustycrayfishcellsWhiletheamountofDNAremainsmostlyconstantincellsregardlessofcon-ditionstheamountofRNApositivelycorrelateswiththeamountofproteinsynthesis(anabolicactivity)ThereforetheratiooftheamountofRNAtothatofDNAinacellisaneffectiveeco-physiologicalindi-catorofcondition (hereafterphysiological condition) that reflects theorganismspotential investment in somatic growthandgametepro-duction (ie fertility) under a given set of environmental conditions(KoopWinkelmannBeckerHellmannampOrtmann2011)
Environmental conditions at each site were characterisedbymeasuringwater depth temperature and velocity aswell asbenthic chlorophyll a concentration of green algae and diatomsat 10 points along a transect perpendicular to the river banksThebenthic concentrationof chlorophylla is a proxyof benthicalgalbiomass (DoddsSmithampLohman2002)measuredusingaBenthotorch (Kahlert ampMcKie 2014) The biomass of macroin-vertebrateswas alsoquantified at all siteswhere crayfish tissuesamples were taken The abundance of macroinvertebrates wasassessedbytakingthree009-m2standardisedsamplesinrunsandriffleswithaD-framekicknetAllmacroinvertebratesampleswerethenwashedthrough05mmsievesandpreservedin70ethanol
23emsp|emspStable isotope analysis
Stable isotope analysiswas conducted on rusty crayfish tissuesand mayfly whole specimens to assess differences in crayfishfeedingpatterns throughout their invasiongradientAll sampleswerepreparedforisotopeanalysisusingstandardprotocolswiththeexceptionof the salt-basedpreservation a field-appropriatemethod that results inminimal anddirectionallyuniformeffectson δ13C and δ15N (Arrington ampWinemiller 2002) Prior to pro-cessingallcrayfishmuscletissuesandmayflywholebodieswererinsedwith distilledwater until the salt was dissolved Sampleswere then dried at 60degC for 24hr ground to powder and sentfornitrogenisotopeanalysistotheUniversityofCaliforniaDavisStableIsotopeFacilityThetrophicpositionofeachcrayfishatsite(S)wasestimatedaccordingto
where254istherustycrayfishdiscriminationfactororfractiona-tionfactor(Δ)representingtheabsolutedifferenceinδ15Nbetweenrusty crayfish and its diet determined in laboratory based on analgaediet(GlonLarsonampPangle2015)Weappliedasinglefrac-tionationfactortoalltrophiclinksofthefoodwebbetweenprimaryconsumersandcrayfishanddidnotaccountforfractionationdiffer-encesamongcrayfishdietsduetoalackofmorespecificreferencevalues
24emsp|emspRNADNA analysis
TheprocedurefortheextractionandquantitationofnucleicacidsinrustycrayfishtissueswasadaptedfromBerdaletRoldaacutenOlivarand Lysnes (2005) andVrede Persson andAronsen (2002) usingfluorochromesthatindiscriminatelybindtoDNAandRNAWepro-vide a brief description below but refer the reader to SupportingInformation AppendixS1 for a more detailed protocol BerdaletRoldaacutenandOlivar(2005)recommendusingthreeseparatealiquotsofeachsampletocomputethequantityofRNAandDNAincrus-taceantissuesthefirstassaymeasuresRNAafterDNAdigestionthesecondmeasuresDNAafterRNAdigestionandthethirdmeas-ures residual fluorescence after digestion of bothDNA andRNAFournucleicacidstandardcurveswithsixconcentrationseachwerethus run foreverybatchof samplesRNA+DNaseRNA+RNaseDNA+RNaseandDNA+DNaseToquantifyRNAandDNAfluo-rescence 50μl of diluted (1200) Quant-iTtrade RiboGreenreg reagentwas added to each platewell The slopes of the standard curveswerethenestimatedusinglinearregressionandthequantityofRNA(μgRNAmlassay)DNA(μgDNAmlassay)andtheirratioineachsample was calculated using the equations provided by BerdaletRoldaacutenandOlivar(2005)
25emsp|emspMacroinvertebrate biomass
Macroinvertebrate ash-free dry weight (AFDW)was estimated ateveryothersitealongthelengthoftheinvasiongradienttoreflectthepreybiomassavailableforconsumptionbyrustycrayfishoneofthemainenvironmentaldriversofcrayfishtrophicposition(Olssonetal 2008) Macroinvertebrates were sorted using a stereo mi-croscopeandseparatedfromothermaterial found inthesamplesSortedmacroinvertebrateswerethenrinsedwithdistilledwateranddriedinanovenat60degCfor48hrweighedcombustedinamufflefurnace at 550degC for 4hr (Mason LewisampWeber 1983) cooleddowntoroomtemperatureinadesiccatorfor6hrandreweighedAshmass (after combustion in furnace)was then subtracted fromdrymass(beforecombustion)toobtainAFDW
26emsp|emspData analysis
Thegoalof this studywas toassesswhetheraphenotypic shifthas occurred along the invasion gradient of rusty crayfish andwhether thisshift isbestexplainedby the rangeexpansionpro-cess or by longitudinal gradients in environmental conditions
(1)
Trophic positioncrayfishS
=2+
15NcrayfishSminus
(
sum3
mayfly=115Nmayfly S
)
∕3
254
6emsp |emsp emspensp MESSAGER And OLdEn
Environmentalconditionsandthespeedofrustycrayfishspreaddiffered among tributaries so each invasion leading edge wasanalysedseparately Intotalfour leading-edgepopulationswereanalysedonedownstreamedge in themainstemJDRand threeupstream edgesmdashin the mainstem South Fork and North ForkJDR(Figure1)
Sixtraitswereanalysedthroughouttheinvasionextentofrustycrayfish carapace length chela length weight trophic positionphysiologicalconditionandsexratio(theproportionofmalesatasite)Onlydataforcrayfishcaughtbykick-seininghand-nettingandsnorkellingwereincludedintheanalysisduetotheknownsizeandsexbiasoftrappingforlargemales(LarsonampOlden2016)Tocon-trolforthestrongrelationshipbetweenbodysizecrayfishweightandchelalengthduetoallometricgrowthresidualsfromcarapacelength-weightandcarapace length-chela lengthnon-linear regres-sionmodels developed separately for each sexwere used as re-sponsevariablesinthemodels(hereafterrelative weight and relative chela length)
A subset of the variablesmeasured at each site was selectedas potential environmental predictors of crayfish trait values theestimatednumberofdegreedays fromAugust2015 toJuly2016(degC)macroinvertebrate AFDW (mg) and chlorophyll a concentra-tion frombenthicgreenalgaeanddiatoms (μgChl-acm2)Degreedayswerecomputedbasedonwater temperatureestimated froma multiple regression model using satellite-measured daily land-surfacetemperaturecalendardaycatchmentareaandelevationaspredictorvariables (MessagerampOlden2018) In situ temperaturemeasurementswere not used in this analysis as diel temperaturevariationswereofthesameorderofmagnitudeasdifferencesbe-tween upstream and downstream sites Velocity and depth mea-surementswerenotincludedintheanalysiseitherduetotheirhighspatialvariabilityatbaseflowintheJDROnlythesitesforwhichallvariableshadbeenmeasuredwereincludedintheanalysisforatotalof18sites14sitesinthemainstemJDRtwointheSouthForkJDRandtwointheNorthForkJDR
In the South Fork andNorth Fork JDRwhere tissue samplesweretakenfromcrayfishinonlytwositesdifferencesintraitvaluesamongsiteswere testedusing two-sample t-testsanddifferencesinsexratiowereassessedwithYatesχ2testInthemainstemJDRgeneralisedadditivemodels(GAMs)weredevelopedtoanalysethedrivers of crayfish morphology physiological condition and tro-phicpositionGAMswerebuiltseparatelyfortwomaincategoriesofpredictorvariablesAfirstcategoryofmodelswasdevelopedtoaccountfortheroleoftherangeexpansionprocessindrivingphe-notypicchangesbyusingeachsitesdistancefromtheinitiallocationofrustycrayfishintroductionasthepredictorvariableThesecondmodel categorywas based on environmental variables thatmightinfluence trait valuesAdditionalmodelswerealsobuiltusingdis-tance from the initial introduction location togetherwith crayfishdensityandsex ratioaspredictorvariablesorcombiningmultipleenvironmentalvariablesThesignificanceandfitofcandidatemod-els(Akaikeinformationcriterionthep-valueofthecoefficientsandtheadjustedR2seeSupportingInformationTableS32)werethen
31emsp|emspCrayfish distribution and habitat conditions
Intotal1266crayfishwerecapturedacrossthe18sitesanalysedin thisstudyofwhich299weresampledformorphological traits259 forphysiological condition and254 for trophicpositionOursurveycombinedwithhistoricaldistributionrecordsandamodelofrustycrayfishspreadintheJDR(MessagerampOlden2018)showedthatrustycrayfishspreadatanacceleratingratesinceitsintroduc-tion and occupied at least 705km of river across the JDR catch-ment inAugust2016Bythatsummer ithadspreadnearly30kmupstreamintheNorthForkandSouthForkJDRandcolonisedthemainstem along a 250km stretch downstream of its introductionpoint(Figure1)Incontrasttoitsextensivespreaddownstreamtheupstreamspreadofrustycrayfishinthemainstemhadbeentempo-rarilyhaltedatthetimeofthesurveyduetoalow-headdam12kmupstream of the putative site of crayfish introduction Densitiesdownstream of the dam were similar to those found at the coreoftheir rangeTherefore theupstreammainsteminvasion leadingedgewasnotincludedinthisanalysisInadditionthepreciseloca-tionofthedownstreammainstemleadingedgecouldnotbedeter-minedduetolimitedaccesstotheriverthusthedownstream-mostsurveyedsitewhererustycrayfishwasfoundinthemainstemwastreatedasthedownstreamedgeoftheirrangeinthisstudy
There was a consistent decrease in rusty crayfish densitiesamongthesampledtributariesfromtheirinitiallocationofintroduc-tiontotheir invasionfrontsRustycrayfishdensities (measuredaskick-seiningcatchperuniteffortFigure2)werehighestinboththemainstem and South Fork JDR (gt30crayfishm2) 40ndash75kmdown-streamoftheinitialsiteofrustycrayfishestablishmentbutrapidlydroppedbyanorderofmagnitudebeyond60kmintheSouthForkJDRandbeyond80kminthemainstemandNorthForkJDRNativesignalcrayfishwerefoundinsympatrywithrustycrayfishinonlyafewsitesattheupstreaminvasionfrontswhererustycrayfishwerefound at lower densities (in the South Forkmainstem and othersmaller side tributaries of the JDR)Where native signal crayfishwerepresent theyoccurredatvery lowdensities (lt2crayfishm2) including in sites without rusty crayfish These findings togetherwithpastrecords (2013)ofsignalcrayfishoccurrence insympatrywithrustycrayfishatsiteswheresignalcrayfishwereabsentduringour2016surveysuggestthatsignalcrayfishisrapidlyexcludedfromsites invadedbyrustycrayfishas itspreadsacrosstheJDRcatch-mentThereforeinterspecificcompetitionwasnotconsideredasig-nificantmechanisminfluencingthetraitsinvestigatedinthisstudy
Temperature and macroinvertebrate biomass followed similarlongitudinalgradients fromupstreamtodownstreambetweenthemainstemSouthFork andNorthFork JDRwhereasbenthicbio-massofgreenalgaeanddiatomwerehighlyvariableamongtribu-taries (Supporting InformationFigureS21)Degreedays increased
emspensp emsp | emsp7MESSAGER And OLdEn
monotonically downstream while macroinvertebrate biomass de-creaseddownstreamTherewasalsoconsiderablevariabilityinmac-roinvertebrate biomass among adjacent sites including a suddenincreaseinbiomassdownstreamfromtheconfluenceofthemain-stemandtheNorthForkJDRwherelowcrayfishdensitiesprevailedGreenalgaeweresparsetoabsentinalltributariesThebiomassofdiatomsontheotherhandwashighestintheSouthForkandupper
mainstemJDR(upto45μgChl-acm2) and low in the lower main-stemandNorthForkJDRwith inconsistent longitudinalgradientsamongtributaries
32emsp|emspMorphology
Therewereconsistenttrendsinrustycrayfishmorphologyfromcore to leading-edge populations in all tributaries (Figure 4SupportingInformationAppendixS3)Therelativechelalengthof rusty crayfish in leading-edge populationswas significantlysmaller than those behind the front in all three tributaries(Mainstem GAM p=003 R2-adjusted=028 n=14 NorthFork t=217 df=29 p=004 South Fork t=303 df=42plt001 Figures3 and 4 Supporting Information TablesS31and S32) Crayfish density was also strongly and positivelyassociatedwith chela length across the JDR (MainstemGAMp=001 R2-adjusted=037 n=14 Figure4 SupportingInformation TableS32) No consistent difference was foundin mean carapace length between core and invasion frontpopulations of the JDR or betweenmale and female crayfishhowever there was a consistent decrease in carapace lengthvariance in thedirectionof the invasion inbothupstreamanddownstream dispersing populations (Figure4 SupportingInformationAppendixS3)Crayfishrelativeweightsignificantlydecreased towards the invasion front both downstream in themainstem (GAM p=004 R2-adjusted=025 n=14) and up-stream in the North Fork (W=177 p=001) and South Fork(W=328 p=001 Supporting Information FigureS41) alongwith decreasing crayfish density (Mainstem GAM p=002R2-adjusted=033 n=14 Figure4 Supporting InformationTableS32)Lastlytherewasnosignificanttrendinthepropor-tionofmalestowardsthefrontsoftheinvasiondespiteaslightincrease inmaledominance inbothupstreamanddownstreamleading edges when considering all sites where gt10 crayfishwerecaptured(SupportingInformationFigureS42)
EnvironmentalconditionswerenotstrongpredictorsofcrayfishmorphologythroughouttheirinvasiongradientDegreedaysdidnotcorrelateconsistentlyacross invasion frontswithanymorphologi-cal trait values (Figure4 Supporting Information TableS32) Forinstancewhiledecreasingupstream temperatureswerepositivelycorrelatedtorelativeweightintheSouthForkandNorthForkJDRtemperatureand relativeweightwerenegativelycorrelated in themainstemSimilarly inconsistentpatternswereobservedbetweentemperature and both relative chela length and carapace lengthMacroinvertebrate biomass (AFDW) was negatively but not sig-nificantly correlated with relative chela length and weight acrosstributariesandwasnotconsistentlyorsignificantlyassociatedwithshifts in carapace length across tributaries (Figure4 SupportingInformationTablesS31andS32)Finallywhilegreenalgaebiomasswasnotconsistentlycorrelatedwithanymorphologicaltraitvaluesdiatombiomasswaspositivelycorrelatedwithrelativechelalengthandweight throughout the JDR (Figure4 Supporting InformationTable S32)
F IGURE 3emspChangesinmeancrayfishrelativechelalength(a)trophicposition(b)andphysiologicalcondition(cRNADNAratioexpressingpotentialforsomaticgrowthandgameteproduction)alongtheinvasiongradientofrustycrayfishintheJohnDayRivercatchmentThesmoothsolidlineandshadedregionrepresentthepredictedmeantraitvalueand95Bayesiancredibleintervalrespectivelyfromageneralisedadditivemodelandasterisksdenotesignificantdifferencesinmean(ple001ple005)VerticaldashedlinesrepresenttheconfluencesoftheSouthFork(at44km)andNorthFork(at87km)withthemainstemJohnDayRiver
8emsp |emsp emspensp MESSAGER And OLdEn
33emsp|emspTrophic position
Thetrophicpositionofrustycrayfishwasconsistentlylowerforin-dividualsat invasion fronts than inpopulationscloser to thecoredespite wide variations among sites throughout the catchment
(Figures3band4SupportingInformationAppendixS3)Inthemain-stemrustycrayfishdietfirstincreaseddownstreamfromthattypi-calofasecondaryconsumeroromnivore(trophicpositionofc 3) to thatofatopcarnivore(trophicpositionofc4)andthendecreasedtowardsthefrontoftheinvasiondowntothatofaprimaryconsumer
F IGURE 4emspSummary of the relationshipsbetweenrustycrayfishtraitsandpredictorvariablesintheJohnDayRiver The direction and colour of the arrowsindicatethesignoftherelationship(egredupwardarrowsreflectpositiverelationships)betweenthepredictorvariable(columns)andthetrait(rows)foragiveninvasionleadingedge(downstreammainstemupstreamSouthForkorupstreamNorthFork)Greyarrowsshowstatisticallynon-significantrelationshipsSignificanceandaconsistentdirectionintherelationshipbetweencandidatepredictorsandtraitsamongtributariessuggestedtheprimacyofthatpredictorindrivingobserveddifferencesintraitsSeeSupportingInformationAppendixS3fordetailedstatisticalresultsFlatgreenarrowsshowvariablesforwhichtherewasnodifferenceamongsitesinthattributaryandrelationshipsdenotedbyandashwerenottestedduetoalackofhypothesisedmechanismsrelatingthevariablesdaggerAsh-freedryweight
Response variable Edge
Predictor variableDistance
from introduction
Crayfish density
Degree days
Macroinv AFDWdagger
Green algae Diatom
Relative chela length
Mainstem
South Fork
North Fork
Trophic position
Mainstem
South Fork
North Fork
Physiological Condition
(RNADNA)
Mainstem
South Fork
North Fork
Carapace length
Mainstem
South Fork
North Fork
Relative weight
Mainstem
South Fork
North Fork
Sex ratio( males)
Mainstemndash ndash ndash ndash ndash
South Forkndash ndash ndash ndash ndash
North Forkndash ndash ndash ndash ndash
Carapace length SD
Mainstemndash ndash ndash ndash
South Forkndash ndash ndash ndash
North Forkndash ndash ndash ndash
daggerAsh-free dry weight
emspensp emsp | emsp9MESSAGER And OLdEn
(trophicpositionofc2GAMp=005R2-adjusted=044n = 14 Figure3b) Therewas an equivalent drop in crayfish trophic posi-tionintheNorthForkJDRupstreamleadingedge(t=966df=22plt0001)butnoequivalentdecreaseintheSouthForkJDRleadingedgeTherewasnodifferenceintrophicpositionamongmaleandfemalecrayfishandalthoughtrophicpositionwasweaklycorrelatedwithcarapacelengthwithinsites(carapacelengthfixedeffect95CI=80times10minus3to19times10minus2trophiclevelmminlinearmixedeffectmodelwithsiteasrandomeffect)therewasnosignificantcorrela-tionbetweentrophicpositionandmeancarapacelengthacrosssitesalongthemainstemTrophicpositionwasnotsignificantlycorrelatedwithrelativechelalengthwithinsites(relativechelalengthfixedef-fect 95 CI=minus83times10minus3 to 23times10minus2 trophic levelmm in linearmixedeffectmodelwithsiteasrandomeffect)
Temperature increasing with downstream distance from theinvasionsourcewascorrelatedwithtrophicpositiononlytowardstheupstreaminvasionfrontsintheNorthForkandSouthForkJDR(Figure4Supporting InformationAppendicesS2andS3)Noneoftheotherenvironmentalvariablessignificantlycovariedwithtrophicpositioninaconsistentwayacrosstributaries(Figure4SupportingInformationAppendicesS2andS3)
34emsp|emspGrowth and condition
There was a consistent positive trend in rusty crayfish physi-ological condition (RNADNA ratio) towards invasion fronts alongwith decreasing crayfish densities (Figures3c and 4 SupportingInformationAppendixS3)Strongesttowardstheupstreamleadingedgesdespitedecreasing temperature (t-test SouthForkW=46p-value=001North Fork t=minus491df=155plt0001) the in-creaseinphysiologicalconditionwasonlymarginalinthemainstem[GAMp=019R2-adjusted=006n=14meanslope=63times10minus3 (95CI=minus27times10minus3to15times10minus2) [RNADNA]km]Thenegativecorrelation between crayfish physiological condition (RNADNAratio)andcrayfishdensityinthemainstemwasalsonon-significant(GAM p=043 R2-adjusted=minus003 n=14) Lastly environmen-tal variables (abiotic and biotic)were not consistently and signifi-cantlyassociatedwithRNADNAratioacrosstributaries(Figure4SupportingInformationAppendixS3)
4emsp |emspDISCUSSION
Thisstudyrevealedsignificanttrendsinmorphologicaltraitvaluesphysiologicalconditionandtrophicpositionofrustycrayfishfromtheirlocationofinitialintroductiontomultipleleadingedgesofinva-sionintheonlyknownpopulationofthisspeciesinwesternNorthAmericaEventhoughthesetrendswerenotconsistentlysignificantacrosstributariestheysuggestthatrustycrayfishindividualsatthevanguard of the invasion exhibited less competitive morphology(decreasedrelativeweightandchelalength)andexploitedenergeticpathwaysloweronthefoodchainyetwereinbetterphysiologicalcondition than individuals located closer to the invasion coreWe
contendthatthesephenotypicshiftsobservedinrustycrayfishareprobablydue to the rangeexpansionprocess itself rather than tonovelenvironmentalconditionsattheirrangeboundariesandthatthesetrendsmayintensifyastheinvasioncontinuestounfoldup-stream and downstream towards the main stem of the ColumbiaRiver
The observed decrease in crayfish relative chela length andweighttowardstheinvasionfrontscanbeattributedtothreemainreasonsmdashalthough further research is needed to confirm the re-spectivecontributionifanyofeachofthesemechanismsFirsttherangeexpansionofrustycrayfishmightbedrivenbytheexclusionof subdominant individuals from high-density population centresthereforeleadingtothewidespreadpresenceofcompetitivelyinfe-riorcrayfishattheinvasionleadingedge(HudinaHockampZganec2014)Inotherwordsindividualcrayfishwithlesscompetitivephe-notypesmayhavebeenforcedoutandsystematically interbredatthe invasionfront resulting in theaccumulationof relatively lightsmall-clawedindividualsattheleadingedgeInsupportofthismech-anismsignalcrayfishattheboundaryoftheirinvasionrangeacrossCroatiadisplaylowerlevelsofaggressionandoftenloseagonisticin-teractionstoindividualsfromtheinvasioncoredespitebeinginbet-ter physical condition (Hudinaetal 2015)However a significantincreaseinrelativeclawsizeawayfromsourcepopulationwasalsoobservedininvasivesignalcrayfishmalesoftheMuraRiverCroatia(Hudinaetal2012)Secondlargerchelaeandastouterbodyshapemay be associated with weaker dispersal ability and thus be se-lectedagainstthroughassociativematingofthefastestdispersersclusteredattheinvasionleadingedgeCrayfishwithshorterchelaeandmorefusiformbodyarebetterabletowithstandhighwaterve-locitiesassuggestedbymorphologicdifferencesbetweencrayfishfound in high-velocity streams compared to those in low-velocitystreams and lakes (Perry etal 2013) Becausewater velocities inexcessof03ndash05msleadtodecreasedcrayfishmovementandpo-tentially increasedenergyexpenditureincrayfish(ClarkKershnerampHolomuzki 2008Matheramp Stein 1993 Perryamp Jones 2017)individualswithshorterchelaeandmorefusiformbodiesmaythusbeabletodisperseforlongerperiodsoftheyearintheJDRwhosedischarge isunregulatedbydamsandflowregimeischaracterisedbyspringsnowmeltThirdlowrustycrayfishconspecificdensitiesat invasion front sitesmay relax the constraints imposedby com-petitioninhigh-densityareasandthusreducetherequirementforinvestment in traitsassociatedwithcompetitionShelterandfoodlimitationsarethemaindriversofagonisticinteractionsincrayfish(BergmanampMoore2003CapelliampHamilton1984)Whentheseresourcesareplentiful inpioneerpopulationsbehaviouralpheno-typesassociatedwithlargeclawsandweightaspartofanaggressionsyndrome(Hudinaetal2012)couldthereforeleadtounnecessaryenergyexpensesand reduced foraging leading to reduced fitness(SihCoteEvansFogartyampPruitt2012)Thusashiftinselectivepressuremayhave led toachange in rustycrayfish lifehistoryattheedgeoftheinvasion involvingthereallocationofenergyfromallometricgrowthofcompetitivetraitstoreproductionanddisper-saltraitsnotmeasuredhere(egwalkingleglength)(Phillipsetal
Weconjecturethatashift intheselectionregimeexperiencedbyrustycrayfishfromcoretoleading-edgeareasisthemostprob-ableexplanationforthetrends inrelativechela lengthandweightobservedinthisstudyHoweverwithoutknowledgeoftheheritabil-ityofthecrayfishtraitsexaminedinthisstudyinferenceregardingthespecificmechanisms inoperation isstill limitedTheaccelerat-ingrateofspreadofrustycrayfish intheJDRthe lowpopulationdensities observedwithin several kilometres of the upstream anddownstreaminvasionfrontsandhighphysiologicalfitnessininva-sionfrontpopulationssuggestthatapushedinvasionexcludingsub-dominantcrayfishfromhigherdensityareasisunlikelytoexplaintheobservedtraitdifferencesMoreoverthereislittletonoevidenceoftheinfluenceofchelasizeorrelativebodyweightondispersalspeed(KamranampMoore 2015) Lastly the difference in relativeweightandchelalengthbetweeninvasioncoreandfrontpopulationscouldalsobedrivenbynaturalselectioninhighcrayfishdensitycorepop-ulationsHistoricaldatafromSorenson(2012)combinedwiththisstudy shownodifference inchela length (Supporting InformationFigureS51)butasignificantincreaseinrelativeweightfrom2010to2016atthepresumedsiteofrustycrayfishintroduction(SupportingInformationFigureS52)Thechangesintraitvaluesobservedherearethuslikelytobetheresultsofacombinationofdriversincludingreducedfitnessofcompetitivephenotypesatlowcrayfishdensityselectionforhighrelativeweightinthepopulationcoreandtrade-offsbetweenthesecompetitiveattributesandother traitsassoci-atedwithhigherdispersalability
Theobserved increase in rustycrayfishanabolicactivitymea-suredasRNADNAinleading-edgepopulationsoftheJDRalthoughweak in themainstem indicates that the rangeexpansionprocesshas led to greater somatic growth andor reproductive potentialin pioneer individuals This pattern matches several documentedincreases inbodyconditiongrowthandreproductivepotential insimilarstreaminvasionsbothwithinasingleinvasiongradientandbetweennativeandnon-nativepopulationsWithintheirnon-nativerange invasion front signal crayfish in Croatia and female spiny-cheekcrayfish in theDanubebothdisplayedgreater reproductivepotentials than their counterparts in core areas with the formeralsobeinginbetterconditionandenergeticstatus(Pacircrvulescuetal2015Rebrinaetal2015)Whencomparingnativeandnon-nativepopulationsofrustycrayfishbothlakeandmesocosmexperimentsfoundthatnon-nativeindividualshavehighergrowthratesandlevelsofactivitythantheirnativecongeners(PintorampSih2009Sargentamp Lodge 2014) Nonetheless whether the observed increase inrustycrayfishphysiologicalconditiontowardstheinvasionfront isassociated with greater somatic growth rates or gamete produc-tionremainsunresolvedandwarrantsfurtherinvestigationIndeed
simultaneous increases inconditiongrowthandreproductivepo-tentialarenotuniversalbecauseselectionfordispersalabilityduringrangeexpansionmay lead tounexpected trade-offsFor instancetadpolesandjuvenilesininvasionfrontpopulationsofcanetoadsintropicalAustraliagrowupto31fasterthanthosefromlongeres-tablishedpopulations(Phillips2009)andadultsdemonstratehigherfeeding rates larger fat stores andbetter condition thanconspe-cifics in later invasion stages (Brownetal2013)However lowerreproductiverateshavealsobeendocumentedincanetoadinvasionfrontpopulations(HudsonPhillipsBrownampShine2015)
Itmightseemthathighercrayfishgrowthratestowardstheinva-sionfrontscontradicttheobservedpatternsofreducedweightandchelalengthobservedinpioneercrayfishHoweverselectionforafasterlifestylecoulddecreaseageatmaturityandshortenthelifes-panoftheseinvasionfrontcrayfishwhileselectingagainstallome-tricgrowthofcompetitivemorphologyBothcrayfishgrowth rateandfecundityaredensitydependent(GuanampWiles1999MomotampGowing1977)Thereforeitispossiblethathighgrowthandfe-cundityphenotypeshavearisenfromnaturalselectioninthec 15 generationssincetheirintroductionaspartofadispersalsyndromeassociating rapid development and high fecunditywith dispersivetraits(RonceampClobert2012Stevensetal2013)
Rustycrayfishattheleadingedgesoftheirdistributionallimitsappeartobefeedinglowerinthefoodwebwhencomparedtocon-specifics locatedbehind the invasion frontThispattern stands incontradictionwithmostpreviousstudiesofstreaminvasionsRoundgobiesattheedgeoftheirexpandingrangeconsumemoreoftheirfavouredpreytypethanincentralpopulations(RabyGutowskyampFox2010)andhavehigherδ15Nsignaturesthanthepreviousyearfront(Brandneretal2013)Invasionfrontbloodyredmysidshrimp(Hemimysis anomala)werenotmoreselectiveintheirpreyconsump-tionbutshowedgreaterabilitytolocateandcapturezooplanktonprey than those shrimp in corepopulations (Iacarella etal 2015)ForcrayfishinvasionstrophicnicheshiftshaveonlybeenassessedatthebiogeographicalscaleandoffermixedinsightsInagreementwithourfindingsnon-nativepopulationsofrustycrayfishandvirilecrayfish(Faxonius virilis)appearedtoshowgreaterratesofalgaecon-sumption (despite constant macroinvertebrate prey consumption)thandidnativepopulationsinlaboratoryassays(Glonetal2018)By contrast an intercontinental stable isotope analysis revealedtrophicnicheconservatisminsignalcrayfishbetweenitsnativeandnon-native range (LarsonOldenampUsio 2010) Trophic flexibilityhasbeenshowntobespecies-dependenteveninsympatricnativecrayfishspecies (JohnstonRobsonampFairweather2011)andmaythus not be a consistent characteristic among invasive omnivoreseitherItisunlikelythatcannibalismawidespreadphenomenonincrayfishpopulations(GuanampWiles1998) ledtotheobservedin-creaseintrophicpositioninareaswithhighdensitiesofcrayfishasconspecificdensitywasnotcorrelatedtotrophicpositionintheJDR(Figure4SupportingInformationAppendixS3)Lastlyitisunlikelythatnon-crayfishpredatorsandcompetitorscouldhavedriventhisdownwardshiftinthetrophicpositionofrustycrayfishasthisshiftwasobservedacrossboththedownstream(increasingfishdensity)
Rustycrayfishhada lower trophicpositionevenwhenmacro-invertebrateprey availability increased towards the invasion frontintheNorthForkJDRThispatterncontrastedwithpastevidenceof a positive relationship between macroinvertebrate availabilityand crayfish trophic position (Olsson etal 2008) and greater as-similation efficiencies of invertebrates than other food items bycrayfish (WhitledgeampRabeni 1997)However the lackof signifi-cantdecreaseintrophicpositiontowardstheinvasionfront intheSouth Fork JDR could be due to a counter-effect from increasingmacroinvertebrate biomass upstream Consumption of macroin-vertebrateshasbeen linkedto increases inweightgainandmeta-bolicrates(BondarBottriellZeronampRichardson2005Hilletal1993 McFeeters Xenopoulos Spooner Wagner amp Frost 2011)Nevertheless in these same studies juvenile signal crayfish in anatural settingdisproportionatelyconsumedfoodtypes thatweretheoppositeofthoseshowntobeofmostnutritionalvaluetothem(Bondar etal 2005) and rusty crayfishmortalitywashigheron adietbasedoninvertebratethanoneonperiphytonordetritus(Hilletal 1993) This suggests that high growth might be associatedwith greater physiological stress due tomore frequentmoultingandhigherforagingcostsinnaturalsettingsThuswehypothesisethatenergyintakeandlong-termfitnessofrustycrayfishassociatedwithperiphytonanddetritusconsumptionmaybehigherthanwithmacroinvertebratedietsdespitetheir lowerdigestionefficiencyoftheseresources
Trade-offs can also arise between increased dispersal rates atrangemarginsand the functional responseof thenon-nativecon-sumer due to the high cost of dispersal (Fronhofer amp Altermatt2015)Giventheircurrentrateofspread(c20kmyeardownstreamfrom2010to2016)intheJDR(MessagerampOlden2018)andawin-dowofactivityof8ndash9months(basedonwatertemperaturesinthemainstem)rustycrayfishwouldhavetoachieveanetdownstreamspreadrateof80mdayonaveragewithoutconsideringtimeded-icatedtomatingandjuvenileparentalcareWespeculatethatthispacecouldrestricttheamountoftimeavailableforactivelypreyingoninvertebratesandcouldselectforthosecrayfishbestabletoef-ficientlyfeedandgrowonabundantandaccessiblebasalresourcesIthasalsobeenhypothesisedforstreamfishesthatthosenon-nativespeciesthatcansustaingrowthandreproductiononlow-qualityre-sourcesshouldbebestabletobecomeestablished(GidoampFranssen2007) Incrayfishabroader trophicniche thatexpandedtowardslower trophic levelsmayhaveaffordedcompetitiveadvantages totheintroducedsignalcrayfishoverthenativenoblecrayfishAstacus astacus inSwedishstreams (OlssonStenrothNystromampGraneli2009) Therefore our findings that rusty crayfish at the invasionfrontactmostlyasprimaryconsumerswhileachievinggreaterphys-iologicalconditionmightreflectanincreaseinfeedingefficiencyonbasal resources as a by-product of greater dispersal ability devel-opedthroughtheirrangeexpansionintheJDR
a crucial first step towards developing spatially explicit strategiestocontrol this invasion If thedocumentedphenotypicshifts fromcore to invasion front populations are indeed associatedwith theaccelerating rateof spreadof rusty crayfish then targeting thoseindividualsattheinvasionleadingedgeforremoval(egbytrapping)mightconstraintheaccumulationofdispersivephenotypesintheseareasAccountingforthesephenotypicshiftsinmechanisticmodelsofinvasivespread(egMessagerampOlden2018)couldalsoprovideuswithavirtual laboratorytotesttheeffectivenessofalternativecontrolstrategiesincontainingthespreadofriverineinvaderssuchasrustycrayfish
Our results suggest that low conspecific densities and spatialsortinginleading-edgepopulationsledtoashift inthephenotypeofrustycrayfishtowards lowercompetitiveabilityhigher intrinsicgrowthandorreproductionandgreaterforagingefficiencyonbasalresourcesastheyspreadupstreamanddownstreamintheJDROurstudydesignenabledustolinkmorphologicalandfunctionaltraitstobetterexploretheconsequencesofthisrangeexpansiononinvadedecosystemsWeexpectthatthediminishedcompetitiveabilityob-servedinthevanguardofthisrustycrayfishinvasionmightleadtoreducedfitnessoftheinvasionfrontphenotypesoncedensities innewlycolonisedareas limit theavailabilityofshelterand intensifycompetition formatesThe long-termevolutionary implicationsofthesephenotypicshiftsmightthusbelimited(PerkinsBoettigerampPhillips2016)Howeverthetrophicshiftobservedininvasionfrontpopulationscouldalsoallowrustycrayfishtoreachhigherdensitiesintheseareasastheymightexploitresourcesmorebroadlyandeffi-cientlyundercompetitiveconditionsTheevolutionaryforcesatplayinthisinvasionhaveprobablyinteractedwithlongitudinalgradientsinenvironmentalconditionsinwaysanalogoustothoseexperiencedbyspeciesduringtheirmigrationtowardscoolerareasunderclimatechangeIntegratingthestudyofmorphologicalandfunctionaltraitswith spatial variation in environmental conditions thus provides arobustwaytoassesswhethercontemporaryevolutionisalteringthephenotypeandecosystemimpactsofspeciesastheirrangeexpandsthroughthelandscape
Inconclusionthisstudyaddsevidenceinsupportofphenotypicchangesexpectedinnon-nativeorganismsexposedtochangingse-lectionpressuresas they invadenewenvironmentsDisentanglingthe causes of these changes whether related to environmentalfactorsorselectionduetorangeexpansionremainsan importantareaofinvestigationasweseektobetterunderstandtheecologicalimpactsofinvasivespeciesandhownativespecieswillrespondtoshiftingenvironmentalconditionsinthefuture
ACKNOWLEDG MENTS
WethankJeffAdamsEricLarsonDavidWoosterStephenBollensandKeithSorensonforprovidinghistoricaldataforrustycrayfishthe staff at theGrantCountyAssessorsoffice and the JohnDayFossilBedsNationalMonument for their help accessing the riverParticular appreciation goes to all the landowners throughout theJohnDayRiverbasin foraccess to their landandsupport for this
12emsp |emsp emspensp MESSAGER And OLdEn
projectWearegratefultoJacobCrunkforhisinestimablehelpwithfieldworkandEthenWhattamforhishelpprocessingmacroinver-tebratesamplesFromtheUniversityofWashingtonwethanktheMolecularEcologyResearchLaboratory(MERLab)andmorespecifi-callyIsadoraJimenez-HidalgoandNatalieLowelltheOldenlabaswellasJoshuaLawlerThomasQuinnandPatrickTobinThemanu-scriptwasimprovedbythecommentsfromtwoanonymousreview-ersFundingsupportwasprovidedbytheJohnNCobbScholarshipin Fisheries the Simpson Award from the Society for FreshwaterScienceandtheCrustaceanSocietyfellowshipinGraduateStudiesawarded to MLM and the University of Washington H MasonKeelerEndowedProfessorshipawardtoJDO
Mathis L Messager httpsorcidorg0000-0002-3051-8068
Julian D Olden httpsorcidorg0000-0003-2143-1187
R E FE R E N C E S
AndersonCampCabanaG (2007)Estimatingthetrophicpositionofaquatic consumers in river food webs using stable nitrogen iso-topes Journal of the North American Benthological Society 26(2)273ndash285 httpsdoiorg1018990887-3593(2007)26[273ettpoa]20co2
Arrington D A ampWinemiller K O (2002) Preservation effects onstable isotope analysis of fishmuscleTransactions of the American Fisheries Society131(2)337ndash342httpsdoiorg1015771548-8659(2002)131lt0337peosiagt20co2
Berdalet E Roldaacuten C ampOlivarM P (2005) Quantifying RNA andDNAinplanktonicorganismswithSYBRGreenIIandnucleasesPartBQuantification in natural samplesScientia Marina69(1) 17ndash30httpsdoiorg103989scimar200569n117
BerdaletERoldaacutenCOlivarMPampLysnesK (2005)QuantifyingRNAandDNAinplanktonicorganismswithSYBRGreenIIandnu-cleases Part A Optimisation of the assay Scientia Marina 69(1)1ndash16httpsdoiorg103989scimar200569n11
Bobeldyk A M amp Lamberti G A (2010) Stream food web re-sponses to a large omnivorous invader Orconectes rusticus (Decapoda Cambaridae) Crustaceana 83(6) 641ndash657 httpsdoiorg101163001121610x491031
BondarCABottriellKZeronKampRichardsonJS(2005)Doestro-phicpositionof theomnivoroussignalcrayfish (Pacifastacus lenius-culus) inastreamfoodwebvarywith lifehistorystageordensityCanadian Journal of Fisheries and Aquatic Sciences62(11)2632ndash2639httpsdoiorg101139f05-167
BrandnerJCerwenkaAFSchliewenUKampGeistJ(2013)BiggerisbetterCharacteristicsofroundgobiesforminganinvasionfrontinthe Danube River PLoS ONE8(9)e73036httpsdoiorg101371journalpone0073036
BrownGPKelehearCampShineR (2013)Theearly toadgets theworm Cane toads at an invasion front benefit from higher preyavailability Journal of Animal Ecology 82(4) 854ndash862 httpsdoiorg1011111365-265612048
Burton O J Phillips B L amp Travis J M J (2010) Trade-offs and the evolution of life-histories during range ex-pansion Ecology Letters 13(10) 1210ndash1220 httpsdoiorg101111j1461-0248201001505x
Capelli G M amp Hamilton P A (1984) Effects of food shelter andtimeof dayon aggressive activity in the crayfishOrconectes rusti-cus(Girard)Journal of Crustacean Biology4(2)252ndash260httpsdoiorg1011631937240x84x00363
Caplat P Cheptou P O Diez J Guisan A Larson B MMacDougall A S hellip Zhang R (2013) Movement impacts andmanagement of plant distributions in response to climate changeInsights from invasions Oikos 122(9) 1265ndash1274 httpsdoiorg101111j1600-0706201300430x
Chuang A amp Peterson C R (2016) Expanding population edgesTheories traits and trade-offsGlobal Change Biology22(2) 494ndash512httpsdoiorg101111gcb13107
ClarkJMKershnerMWampHolomuzkiJR(2008)Grainsizeandsorting effects on size-dependent responses by lotic crayfish tohigh flows Hydrobiologia 610 55ndash66 httpsdoiorg101007s10750-008-9422-0
CrandallKAampDeGraveS (2017)Anupdatedclassificationofthefreshwater crayfishes (Decapoda Astacidea) of the world with acompletespecieslistJournal of Crustacean Biology37(5)615ndash653httpsdoiorg101093jcbiolrux070
DavidsonAMJennionsMampNicotraAB(2011)Doinvasivespe-cies show higher phenotypic plasticity than native species and ifso is it adaptiveAmeta-analysisEcology Letters14(4) 419ndash431httpsdoiorg101111j1461-0248201101596x
DoddsWK Smith VH amp Lohman K (2002)Nitrogen and phos-phorusrelationshipstobenthicalgalbiomassintemperatestreamsCanadian Journal of Fisheries and Aquatic Sciences 59(5) 865ndash874httpsdoiorg101139f02-063
Fronhofer E A amp Altermatt F (2015) Eco-evolutionary feedbacksduring experimental range expansions Nature Communications 66844httpsdoiorg101038ncomms7844
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
emspensp emsp | emsp5MESSAGER And OLdEn
inourestimatesofrelativedensityWhencrayfishdensitywashighmorphologicalmeasurementswererecordedforarandomsubsampleof30ofthecrayfishthatwerecaughtbykick-seiningThefirsttissuesamplewasimmediatelystoredinnon-iodisedsaltforsubsequentδ15Nstableisotopeanalysistodeterminethetrophicpositionofrustycray-fishatthatsitemdashtheenergy-weightednumberoftrophicenergytrans-fersfromprimaryproducertocrayfish(VanderZandenampRasmussen1999) We also collected 12ndash20 mayfly nymphs (EphemeropteraHeptageniidae)inrunsandrifflesateachstudysitewherecrayfishtis-suesweresampledtocharacterisethebaselineδ15NvaluesofprimaryconsumersthroughouttheJDR(AndersonampCabana2007)Thesec-ondtissuesamplepreservedinRNAlaterregwasusedtoquantifytherelativeconcentrationofRNAandDNAinrustycrayfishcellsWhiletheamountofDNAremainsmostlyconstantincellsregardlessofcon-ditionstheamountofRNApositivelycorrelateswiththeamountofproteinsynthesis(anabolicactivity)ThereforetheratiooftheamountofRNAtothatofDNAinacellisaneffectiveeco-physiologicalindi-catorofcondition (hereafterphysiological condition) that reflects theorganismspotential investment in somatic growthandgametepro-duction (ie fertility) under a given set of environmental conditions(KoopWinkelmannBeckerHellmannampOrtmann2011)
Environmental conditions at each site were characterisedbymeasuringwater depth temperature and velocity aswell asbenthic chlorophyll a concentration of green algae and diatomsat 10 points along a transect perpendicular to the river banksThebenthic concentrationof chlorophylla is a proxyof benthicalgalbiomass (DoddsSmithampLohman2002)measuredusingaBenthotorch (Kahlert ampMcKie 2014) The biomass of macroin-vertebrateswas alsoquantified at all siteswhere crayfish tissuesamples were taken The abundance of macroinvertebrates wasassessedbytakingthree009-m2standardisedsamplesinrunsandriffleswithaD-framekicknetAllmacroinvertebratesampleswerethenwashedthrough05mmsievesandpreservedin70ethanol
23emsp|emspStable isotope analysis
Stable isotope analysiswas conducted on rusty crayfish tissuesand mayfly whole specimens to assess differences in crayfishfeedingpatterns throughout their invasiongradientAll sampleswerepreparedforisotopeanalysisusingstandardprotocolswiththeexceptionof the salt-basedpreservation a field-appropriatemethod that results inminimal anddirectionallyuniformeffectson δ13C and δ15N (Arrington ampWinemiller 2002) Prior to pro-cessingallcrayfishmuscletissuesandmayflywholebodieswererinsedwith distilledwater until the salt was dissolved Sampleswere then dried at 60degC for 24hr ground to powder and sentfornitrogenisotopeanalysistotheUniversityofCaliforniaDavisStableIsotopeFacilityThetrophicpositionofeachcrayfishatsite(S)wasestimatedaccordingto
where254istherustycrayfishdiscriminationfactororfractiona-tionfactor(Δ)representingtheabsolutedifferenceinδ15Nbetweenrusty crayfish and its diet determined in laboratory based on analgaediet(GlonLarsonampPangle2015)Weappliedasinglefrac-tionationfactortoalltrophiclinksofthefoodwebbetweenprimaryconsumersandcrayfishanddidnotaccountforfractionationdiffer-encesamongcrayfishdietsduetoalackofmorespecificreferencevalues
24emsp|emspRNADNA analysis
TheprocedurefortheextractionandquantitationofnucleicacidsinrustycrayfishtissueswasadaptedfromBerdaletRoldaacutenOlivarand Lysnes (2005) andVrede Persson andAronsen (2002) usingfluorochromesthatindiscriminatelybindtoDNAandRNAWepro-vide a brief description below but refer the reader to SupportingInformation AppendixS1 for a more detailed protocol BerdaletRoldaacutenandOlivar(2005)recommendusingthreeseparatealiquotsofeachsampletocomputethequantityofRNAandDNAincrus-taceantissuesthefirstassaymeasuresRNAafterDNAdigestionthesecondmeasuresDNAafterRNAdigestionandthethirdmeas-ures residual fluorescence after digestion of bothDNA andRNAFournucleicacidstandardcurveswithsixconcentrationseachwerethus run foreverybatchof samplesRNA+DNaseRNA+RNaseDNA+RNaseandDNA+DNaseToquantifyRNAandDNAfluo-rescence 50μl of diluted (1200) Quant-iTtrade RiboGreenreg reagentwas added to each platewell The slopes of the standard curveswerethenestimatedusinglinearregressionandthequantityofRNA(μgRNAmlassay)DNA(μgDNAmlassay)andtheirratioineachsample was calculated using the equations provided by BerdaletRoldaacutenandOlivar(2005)
25emsp|emspMacroinvertebrate biomass
Macroinvertebrate ash-free dry weight (AFDW)was estimated ateveryothersitealongthelengthoftheinvasiongradienttoreflectthepreybiomassavailableforconsumptionbyrustycrayfishoneofthemainenvironmentaldriversofcrayfishtrophicposition(Olssonetal 2008) Macroinvertebrates were sorted using a stereo mi-croscopeandseparatedfromothermaterial found inthesamplesSortedmacroinvertebrateswerethenrinsedwithdistilledwateranddriedinanovenat60degCfor48hrweighedcombustedinamufflefurnace at 550degC for 4hr (Mason LewisampWeber 1983) cooleddowntoroomtemperatureinadesiccatorfor6hrandreweighedAshmass (after combustion in furnace)was then subtracted fromdrymass(beforecombustion)toobtainAFDW
26emsp|emspData analysis
Thegoalof this studywas toassesswhetheraphenotypic shifthas occurred along the invasion gradient of rusty crayfish andwhether thisshift isbestexplainedby the rangeexpansionpro-cess or by longitudinal gradients in environmental conditions
(1)
Trophic positioncrayfishS
=2+
15NcrayfishSminus
(
sum3
mayfly=115Nmayfly S
)
∕3
254
6emsp |emsp emspensp MESSAGER And OLdEn
Environmentalconditionsandthespeedofrustycrayfishspreaddiffered among tributaries so each invasion leading edge wasanalysedseparately Intotalfour leading-edgepopulationswereanalysedonedownstreamedge in themainstemJDRand threeupstream edgesmdashin the mainstem South Fork and North ForkJDR(Figure1)
Sixtraitswereanalysedthroughouttheinvasionextentofrustycrayfish carapace length chela length weight trophic positionphysiologicalconditionandsexratio(theproportionofmalesatasite)Onlydataforcrayfishcaughtbykick-seininghand-nettingandsnorkellingwereincludedintheanalysisduetotheknownsizeandsexbiasoftrappingforlargemales(LarsonampOlden2016)Tocon-trolforthestrongrelationshipbetweenbodysizecrayfishweightandchelalengthduetoallometricgrowthresidualsfromcarapacelength-weightandcarapace length-chela lengthnon-linear regres-sionmodels developed separately for each sexwere used as re-sponsevariablesinthemodels(hereafterrelative weight and relative chela length)
A subset of the variablesmeasured at each site was selectedas potential environmental predictors of crayfish trait values theestimatednumberofdegreedays fromAugust2015 toJuly2016(degC)macroinvertebrate AFDW (mg) and chlorophyll a concentra-tion frombenthicgreenalgaeanddiatoms (μgChl-acm2)Degreedayswerecomputedbasedonwater temperatureestimated froma multiple regression model using satellite-measured daily land-surfacetemperaturecalendardaycatchmentareaandelevationaspredictorvariables (MessagerampOlden2018) In situ temperaturemeasurementswere not used in this analysis as diel temperaturevariationswereofthesameorderofmagnitudeasdifferencesbe-tween upstream and downstream sites Velocity and depth mea-surementswerenotincludedintheanalysiseitherduetotheirhighspatialvariabilityatbaseflowintheJDROnlythesitesforwhichallvariableshadbeenmeasuredwereincludedintheanalysisforatotalof18sites14sitesinthemainstemJDRtwointheSouthForkJDRandtwointheNorthForkJDR
In the South Fork andNorth Fork JDRwhere tissue samplesweretakenfromcrayfishinonlytwositesdifferencesintraitvaluesamongsiteswere testedusing two-sample t-testsanddifferencesinsexratiowereassessedwithYatesχ2testInthemainstemJDRgeneralisedadditivemodels(GAMs)weredevelopedtoanalysethedrivers of crayfish morphology physiological condition and tro-phicpositionGAMswerebuiltseparatelyfortwomaincategoriesofpredictorvariablesAfirstcategoryofmodelswasdevelopedtoaccountfortheroleoftherangeexpansionprocessindrivingphe-notypicchangesbyusingeachsitesdistancefromtheinitiallocationofrustycrayfishintroductionasthepredictorvariableThesecondmodel categorywas based on environmental variables thatmightinfluence trait valuesAdditionalmodelswerealsobuiltusingdis-tance from the initial introduction location togetherwith crayfishdensityandsex ratioaspredictorvariablesorcombiningmultipleenvironmentalvariablesThesignificanceandfitofcandidatemod-els(Akaikeinformationcriterionthep-valueofthecoefficientsandtheadjustedR2seeSupportingInformationTableS32)werethen
31emsp|emspCrayfish distribution and habitat conditions
Intotal1266crayfishwerecapturedacrossthe18sitesanalysedin thisstudyofwhich299weresampledformorphological traits259 forphysiological condition and254 for trophicpositionOursurveycombinedwithhistoricaldistributionrecordsandamodelofrustycrayfishspreadintheJDR(MessagerampOlden2018)showedthatrustycrayfishspreadatanacceleratingratesinceitsintroduc-tion and occupied at least 705km of river across the JDR catch-ment inAugust2016Bythatsummer ithadspreadnearly30kmupstreamintheNorthForkandSouthForkJDRandcolonisedthemainstem along a 250km stretch downstream of its introductionpoint(Figure1)Incontrasttoitsextensivespreaddownstreamtheupstreamspreadofrustycrayfishinthemainstemhadbeentempo-rarilyhaltedatthetimeofthesurveyduetoalow-headdam12kmupstream of the putative site of crayfish introduction Densitiesdownstream of the dam were similar to those found at the coreoftheir rangeTherefore theupstreammainsteminvasion leadingedgewasnotincludedinthisanalysisInadditionthepreciseloca-tionofthedownstreammainstemleadingedgecouldnotbedeter-minedduetolimitedaccesstotheriverthusthedownstream-mostsurveyedsitewhererustycrayfishwasfoundinthemainstemwastreatedasthedownstreamedgeoftheirrangeinthisstudy
There was a consistent decrease in rusty crayfish densitiesamongthesampledtributariesfromtheirinitiallocationofintroduc-tiontotheir invasionfrontsRustycrayfishdensities (measuredaskick-seiningcatchperuniteffortFigure2)werehighestinboththemainstem and South Fork JDR (gt30crayfishm2) 40ndash75kmdown-streamoftheinitialsiteofrustycrayfishestablishmentbutrapidlydroppedbyanorderofmagnitudebeyond60kmintheSouthForkJDRandbeyond80kminthemainstemandNorthForkJDRNativesignalcrayfishwerefoundinsympatrywithrustycrayfishinonlyafewsitesattheupstreaminvasionfrontswhererustycrayfishwerefound at lower densities (in the South Forkmainstem and othersmaller side tributaries of the JDR)Where native signal crayfishwerepresent theyoccurredatvery lowdensities (lt2crayfishm2) including in sites without rusty crayfish These findings togetherwithpastrecords (2013)ofsignalcrayfishoccurrence insympatrywithrustycrayfishatsiteswheresignalcrayfishwereabsentduringour2016surveysuggestthatsignalcrayfishisrapidlyexcludedfromsites invadedbyrustycrayfishas itspreadsacrosstheJDRcatch-mentThereforeinterspecificcompetitionwasnotconsideredasig-nificantmechanisminfluencingthetraitsinvestigatedinthisstudy
Temperature and macroinvertebrate biomass followed similarlongitudinalgradients fromupstreamtodownstreambetweenthemainstemSouthFork andNorthFork JDRwhereasbenthicbio-massofgreenalgaeanddiatomwerehighlyvariableamongtribu-taries (Supporting InformationFigureS21)Degreedays increased
emspensp emsp | emsp7MESSAGER And OLdEn
monotonically downstream while macroinvertebrate biomass de-creaseddownstreamTherewasalsoconsiderablevariabilityinmac-roinvertebrate biomass among adjacent sites including a suddenincreaseinbiomassdownstreamfromtheconfluenceofthemain-stemandtheNorthForkJDRwherelowcrayfishdensitiesprevailedGreenalgaeweresparsetoabsentinalltributariesThebiomassofdiatomsontheotherhandwashighestintheSouthForkandupper
mainstemJDR(upto45μgChl-acm2) and low in the lower main-stemandNorthForkJDRwith inconsistent longitudinalgradientsamongtributaries
32emsp|emspMorphology
Therewereconsistenttrendsinrustycrayfishmorphologyfromcore to leading-edge populations in all tributaries (Figure 4SupportingInformationAppendixS3)Therelativechelalengthof rusty crayfish in leading-edge populationswas significantlysmaller than those behind the front in all three tributaries(Mainstem GAM p=003 R2-adjusted=028 n=14 NorthFork t=217 df=29 p=004 South Fork t=303 df=42plt001 Figures3 and 4 Supporting Information TablesS31and S32) Crayfish density was also strongly and positivelyassociatedwith chela length across the JDR (MainstemGAMp=001 R2-adjusted=037 n=14 Figure4 SupportingInformation TableS32) No consistent difference was foundin mean carapace length between core and invasion frontpopulations of the JDR or betweenmale and female crayfishhowever there was a consistent decrease in carapace lengthvariance in thedirectionof the invasion inbothupstreamanddownstream dispersing populations (Figure4 SupportingInformationAppendixS3)Crayfishrelativeweightsignificantlydecreased towards the invasion front both downstream in themainstem (GAM p=004 R2-adjusted=025 n=14) and up-stream in the North Fork (W=177 p=001) and South Fork(W=328 p=001 Supporting Information FigureS41) alongwith decreasing crayfish density (Mainstem GAM p=002R2-adjusted=033 n=14 Figure4 Supporting InformationTableS32)Lastlytherewasnosignificanttrendinthepropor-tionofmalestowardsthefrontsoftheinvasiondespiteaslightincrease inmaledominance inbothupstreamanddownstreamleading edges when considering all sites where gt10 crayfishwerecaptured(SupportingInformationFigureS42)
EnvironmentalconditionswerenotstrongpredictorsofcrayfishmorphologythroughouttheirinvasiongradientDegreedaysdidnotcorrelateconsistentlyacross invasion frontswithanymorphologi-cal trait values (Figure4 Supporting Information TableS32) Forinstancewhiledecreasingupstream temperatureswerepositivelycorrelatedtorelativeweightintheSouthForkandNorthForkJDRtemperatureand relativeweightwerenegativelycorrelated in themainstemSimilarly inconsistentpatternswereobservedbetweentemperature and both relative chela length and carapace lengthMacroinvertebrate biomass (AFDW) was negatively but not sig-nificantly correlated with relative chela length and weight acrosstributariesandwasnotconsistentlyorsignificantlyassociatedwithshifts in carapace length across tributaries (Figure4 SupportingInformationTablesS31andS32)Finallywhilegreenalgaebiomasswasnotconsistentlycorrelatedwithanymorphologicaltraitvaluesdiatombiomasswaspositivelycorrelatedwithrelativechelalengthandweight throughout the JDR (Figure4 Supporting InformationTable S32)
F IGURE 3emspChangesinmeancrayfishrelativechelalength(a)trophicposition(b)andphysiologicalcondition(cRNADNAratioexpressingpotentialforsomaticgrowthandgameteproduction)alongtheinvasiongradientofrustycrayfishintheJohnDayRivercatchmentThesmoothsolidlineandshadedregionrepresentthepredictedmeantraitvalueand95Bayesiancredibleintervalrespectivelyfromageneralisedadditivemodelandasterisksdenotesignificantdifferencesinmean(ple001ple005)VerticaldashedlinesrepresenttheconfluencesoftheSouthFork(at44km)andNorthFork(at87km)withthemainstemJohnDayRiver
8emsp |emsp emspensp MESSAGER And OLdEn
33emsp|emspTrophic position
Thetrophicpositionofrustycrayfishwasconsistentlylowerforin-dividualsat invasion fronts than inpopulationscloser to thecoredespite wide variations among sites throughout the catchment
(Figures3band4SupportingInformationAppendixS3)Inthemain-stemrustycrayfishdietfirstincreaseddownstreamfromthattypi-calofasecondaryconsumeroromnivore(trophicpositionofc 3) to thatofatopcarnivore(trophicpositionofc4)andthendecreasedtowardsthefrontoftheinvasiondowntothatofaprimaryconsumer
F IGURE 4emspSummary of the relationshipsbetweenrustycrayfishtraitsandpredictorvariablesintheJohnDayRiver The direction and colour of the arrowsindicatethesignoftherelationship(egredupwardarrowsreflectpositiverelationships)betweenthepredictorvariable(columns)andthetrait(rows)foragiveninvasionleadingedge(downstreammainstemupstreamSouthForkorupstreamNorthFork)Greyarrowsshowstatisticallynon-significantrelationshipsSignificanceandaconsistentdirectionintherelationshipbetweencandidatepredictorsandtraitsamongtributariessuggestedtheprimacyofthatpredictorindrivingobserveddifferencesintraitsSeeSupportingInformationAppendixS3fordetailedstatisticalresultsFlatgreenarrowsshowvariablesforwhichtherewasnodifferenceamongsitesinthattributaryandrelationshipsdenotedbyandashwerenottestedduetoalackofhypothesisedmechanismsrelatingthevariablesdaggerAsh-freedryweight
Response variable Edge
Predictor variableDistance
from introduction
Crayfish density
Degree days
Macroinv AFDWdagger
Green algae Diatom
Relative chela length
Mainstem
South Fork
North Fork
Trophic position
Mainstem
South Fork
North Fork
Physiological Condition
(RNADNA)
Mainstem
South Fork
North Fork
Carapace length
Mainstem
South Fork
North Fork
Relative weight
Mainstem
South Fork
North Fork
Sex ratio( males)
Mainstemndash ndash ndash ndash ndash
South Forkndash ndash ndash ndash ndash
North Forkndash ndash ndash ndash ndash
Carapace length SD
Mainstemndash ndash ndash ndash
South Forkndash ndash ndash ndash
North Forkndash ndash ndash ndash
daggerAsh-free dry weight
emspensp emsp | emsp9MESSAGER And OLdEn
(trophicpositionofc2GAMp=005R2-adjusted=044n = 14 Figure3b) Therewas an equivalent drop in crayfish trophic posi-tionintheNorthForkJDRupstreamleadingedge(t=966df=22plt0001)butnoequivalentdecreaseintheSouthForkJDRleadingedgeTherewasnodifferenceintrophicpositionamongmaleandfemalecrayfishandalthoughtrophicpositionwasweaklycorrelatedwithcarapacelengthwithinsites(carapacelengthfixedeffect95CI=80times10minus3to19times10minus2trophiclevelmminlinearmixedeffectmodelwithsiteasrandomeffect)therewasnosignificantcorrela-tionbetweentrophicpositionandmeancarapacelengthacrosssitesalongthemainstemTrophicpositionwasnotsignificantlycorrelatedwithrelativechelalengthwithinsites(relativechelalengthfixedef-fect 95 CI=minus83times10minus3 to 23times10minus2 trophic levelmm in linearmixedeffectmodelwithsiteasrandomeffect)
Temperature increasing with downstream distance from theinvasionsourcewascorrelatedwithtrophicpositiononlytowardstheupstreaminvasionfrontsintheNorthForkandSouthForkJDR(Figure4Supporting InformationAppendicesS2andS3)Noneoftheotherenvironmentalvariablessignificantlycovariedwithtrophicpositioninaconsistentwayacrosstributaries(Figure4SupportingInformationAppendicesS2andS3)
34emsp|emspGrowth and condition
There was a consistent positive trend in rusty crayfish physi-ological condition (RNADNA ratio) towards invasion fronts alongwith decreasing crayfish densities (Figures3c and 4 SupportingInformationAppendixS3)Strongesttowardstheupstreamleadingedgesdespitedecreasing temperature (t-test SouthForkW=46p-value=001North Fork t=minus491df=155plt0001) the in-creaseinphysiologicalconditionwasonlymarginalinthemainstem[GAMp=019R2-adjusted=006n=14meanslope=63times10minus3 (95CI=minus27times10minus3to15times10minus2) [RNADNA]km]Thenegativecorrelation between crayfish physiological condition (RNADNAratio)andcrayfishdensityinthemainstemwasalsonon-significant(GAM p=043 R2-adjusted=minus003 n=14) Lastly environmen-tal variables (abiotic and biotic)were not consistently and signifi-cantlyassociatedwithRNADNAratioacrosstributaries(Figure4SupportingInformationAppendixS3)
4emsp |emspDISCUSSION
Thisstudyrevealedsignificanttrendsinmorphologicaltraitvaluesphysiologicalconditionandtrophicpositionofrustycrayfishfromtheirlocationofinitialintroductiontomultipleleadingedgesofinva-sionintheonlyknownpopulationofthisspeciesinwesternNorthAmericaEventhoughthesetrendswerenotconsistentlysignificantacrosstributariestheysuggestthatrustycrayfishindividualsatthevanguard of the invasion exhibited less competitive morphology(decreasedrelativeweightandchelalength)andexploitedenergeticpathwaysloweronthefoodchainyetwereinbetterphysiologicalcondition than individuals located closer to the invasion coreWe
contendthatthesephenotypicshiftsobservedinrustycrayfishareprobablydue to the rangeexpansionprocess itself rather than tonovelenvironmentalconditionsattheirrangeboundariesandthatthesetrendsmayintensifyastheinvasioncontinuestounfoldup-stream and downstream towards the main stem of the ColumbiaRiver
The observed decrease in crayfish relative chela length andweighttowardstheinvasionfrontscanbeattributedtothreemainreasonsmdashalthough further research is needed to confirm the re-spectivecontributionifanyofeachofthesemechanismsFirsttherangeexpansionofrustycrayfishmightbedrivenbytheexclusionof subdominant individuals from high-density population centresthereforeleadingtothewidespreadpresenceofcompetitivelyinfe-riorcrayfishattheinvasionleadingedge(HudinaHockampZganec2014)Inotherwordsindividualcrayfishwithlesscompetitivephe-notypesmayhavebeenforcedoutandsystematically interbredatthe invasionfront resulting in theaccumulationof relatively lightsmall-clawedindividualsattheleadingedgeInsupportofthismech-anismsignalcrayfishattheboundaryoftheirinvasionrangeacrossCroatiadisplaylowerlevelsofaggressionandoftenloseagonisticin-teractionstoindividualsfromtheinvasioncoredespitebeinginbet-ter physical condition (Hudinaetal 2015)However a significantincreaseinrelativeclawsizeawayfromsourcepopulationwasalsoobservedininvasivesignalcrayfishmalesoftheMuraRiverCroatia(Hudinaetal2012)Secondlargerchelaeandastouterbodyshapemay be associated with weaker dispersal ability and thus be se-lectedagainstthroughassociativematingofthefastestdispersersclusteredattheinvasionleadingedgeCrayfishwithshorterchelaeandmorefusiformbodyarebetterabletowithstandhighwaterve-locitiesassuggestedbymorphologicdifferencesbetweencrayfishfound in high-velocity streams compared to those in low-velocitystreams and lakes (Perry etal 2013) Becausewater velocities inexcessof03ndash05msleadtodecreasedcrayfishmovementandpo-tentially increasedenergyexpenditureincrayfish(ClarkKershnerampHolomuzki 2008Matheramp Stein 1993 Perryamp Jones 2017)individualswithshorterchelaeandmorefusiformbodiesmaythusbeabletodisperseforlongerperiodsoftheyearintheJDRwhosedischarge isunregulatedbydamsandflowregimeischaracterisedbyspringsnowmeltThirdlowrustycrayfishconspecificdensitiesat invasion front sitesmay relax the constraints imposedby com-petitioninhigh-densityareasandthusreducetherequirementforinvestment in traitsassociatedwithcompetitionShelterandfoodlimitationsarethemaindriversofagonisticinteractionsincrayfish(BergmanampMoore2003CapelliampHamilton1984)Whentheseresourcesareplentiful inpioneerpopulationsbehaviouralpheno-typesassociatedwithlargeclawsandweightaspartofanaggressionsyndrome(Hudinaetal2012)couldthereforeleadtounnecessaryenergyexpensesand reduced foraging leading to reduced fitness(SihCoteEvansFogartyampPruitt2012)Thusashiftinselectivepressuremayhave led toachange in rustycrayfish lifehistoryattheedgeoftheinvasion involvingthereallocationofenergyfromallometricgrowthofcompetitivetraitstoreproductionanddisper-saltraitsnotmeasuredhere(egwalkingleglength)(Phillipsetal
Weconjecturethatashift intheselectionregimeexperiencedbyrustycrayfishfromcoretoleading-edgeareasisthemostprob-ableexplanationforthetrends inrelativechela lengthandweightobservedinthisstudyHoweverwithoutknowledgeoftheheritabil-ityofthecrayfishtraitsexaminedinthisstudyinferenceregardingthespecificmechanisms inoperation isstill limitedTheaccelerat-ingrateofspreadofrustycrayfish intheJDRthe lowpopulationdensities observedwithin several kilometres of the upstream anddownstreaminvasionfrontsandhighphysiologicalfitnessininva-sionfrontpopulationssuggestthatapushedinvasionexcludingsub-dominantcrayfishfromhigherdensityareasisunlikelytoexplaintheobservedtraitdifferencesMoreoverthereislittletonoevidenceoftheinfluenceofchelasizeorrelativebodyweightondispersalspeed(KamranampMoore 2015) Lastly the difference in relativeweightandchelalengthbetweeninvasioncoreandfrontpopulationscouldalsobedrivenbynaturalselectioninhighcrayfishdensitycorepop-ulationsHistoricaldatafromSorenson(2012)combinedwiththisstudy shownodifference inchela length (Supporting InformationFigureS51)butasignificantincreaseinrelativeweightfrom2010to2016atthepresumedsiteofrustycrayfishintroduction(SupportingInformationFigureS52)Thechangesintraitvaluesobservedherearethuslikelytobetheresultsofacombinationofdriversincludingreducedfitnessofcompetitivephenotypesatlowcrayfishdensityselectionforhighrelativeweightinthepopulationcoreandtrade-offsbetweenthesecompetitiveattributesandother traitsassoci-atedwithhigherdispersalability
Theobserved increase in rustycrayfishanabolicactivitymea-suredasRNADNAinleading-edgepopulationsoftheJDRalthoughweak in themainstem indicates that the rangeexpansionprocesshas led to greater somatic growth andor reproductive potentialin pioneer individuals This pattern matches several documentedincreases inbodyconditiongrowthandreproductivepotential insimilarstreaminvasionsbothwithinasingleinvasiongradientandbetweennativeandnon-nativepopulationsWithintheirnon-nativerange invasion front signal crayfish in Croatia and female spiny-cheekcrayfish in theDanubebothdisplayedgreater reproductivepotentials than their counterparts in core areas with the formeralsobeinginbetterconditionandenergeticstatus(Pacircrvulescuetal2015Rebrinaetal2015)Whencomparingnativeandnon-nativepopulationsofrustycrayfishbothlakeandmesocosmexperimentsfoundthatnon-nativeindividualshavehighergrowthratesandlevelsofactivitythantheirnativecongeners(PintorampSih2009Sargentamp Lodge 2014) Nonetheless whether the observed increase inrustycrayfishphysiologicalconditiontowardstheinvasionfront isassociated with greater somatic growth rates or gamete produc-tionremainsunresolvedandwarrantsfurtherinvestigationIndeed
simultaneous increases inconditiongrowthandreproductivepo-tentialarenotuniversalbecauseselectionfordispersalabilityduringrangeexpansionmay lead tounexpected trade-offsFor instancetadpolesandjuvenilesininvasionfrontpopulationsofcanetoadsintropicalAustraliagrowupto31fasterthanthosefromlongeres-tablishedpopulations(Phillips2009)andadultsdemonstratehigherfeeding rates larger fat stores andbetter condition thanconspe-cifics in later invasion stages (Brownetal2013)However lowerreproductiverateshavealsobeendocumentedincanetoadinvasionfrontpopulations(HudsonPhillipsBrownampShine2015)
Itmightseemthathighercrayfishgrowthratestowardstheinva-sionfrontscontradicttheobservedpatternsofreducedweightandchelalengthobservedinpioneercrayfishHoweverselectionforafasterlifestylecoulddecreaseageatmaturityandshortenthelifes-panoftheseinvasionfrontcrayfishwhileselectingagainstallome-tricgrowthofcompetitivemorphologyBothcrayfishgrowth rateandfecundityaredensitydependent(GuanampWiles1999MomotampGowing1977)Thereforeitispossiblethathighgrowthandfe-cundityphenotypeshavearisenfromnaturalselectioninthec 15 generationssincetheirintroductionaspartofadispersalsyndromeassociating rapid development and high fecunditywith dispersivetraits(RonceampClobert2012Stevensetal2013)
Rustycrayfishattheleadingedgesoftheirdistributionallimitsappeartobefeedinglowerinthefoodwebwhencomparedtocon-specifics locatedbehind the invasion frontThispattern stands incontradictionwithmostpreviousstudiesofstreaminvasionsRoundgobiesattheedgeoftheirexpandingrangeconsumemoreoftheirfavouredpreytypethanincentralpopulations(RabyGutowskyampFox2010)andhavehigherδ15Nsignaturesthanthepreviousyearfront(Brandneretal2013)Invasionfrontbloodyredmysidshrimp(Hemimysis anomala)werenotmoreselectiveintheirpreyconsump-tionbutshowedgreaterabilitytolocateandcapturezooplanktonprey than those shrimp in corepopulations (Iacarella etal 2015)ForcrayfishinvasionstrophicnicheshiftshaveonlybeenassessedatthebiogeographicalscaleandoffermixedinsightsInagreementwithourfindingsnon-nativepopulationsofrustycrayfishandvirilecrayfish(Faxonius virilis)appearedtoshowgreaterratesofalgaecon-sumption (despite constant macroinvertebrate prey consumption)thandidnativepopulationsinlaboratoryassays(Glonetal2018)By contrast an intercontinental stable isotope analysis revealedtrophicnicheconservatisminsignalcrayfishbetweenitsnativeandnon-native range (LarsonOldenampUsio 2010) Trophic flexibilityhasbeenshowntobespecies-dependenteveninsympatricnativecrayfishspecies (JohnstonRobsonampFairweather2011)andmaythus not be a consistent characteristic among invasive omnivoreseitherItisunlikelythatcannibalismawidespreadphenomenonincrayfishpopulations(GuanampWiles1998) ledtotheobservedin-creaseintrophicpositioninareaswithhighdensitiesofcrayfishasconspecificdensitywasnotcorrelatedtotrophicpositionintheJDR(Figure4SupportingInformationAppendixS3)Lastlyitisunlikelythatnon-crayfishpredatorsandcompetitorscouldhavedriventhisdownwardshiftinthetrophicpositionofrustycrayfishasthisshiftwasobservedacrossboththedownstream(increasingfishdensity)
Rustycrayfishhada lower trophicpositionevenwhenmacro-invertebrateprey availability increased towards the invasion frontintheNorthForkJDRThispatterncontrastedwithpastevidenceof a positive relationship between macroinvertebrate availabilityand crayfish trophic position (Olsson etal 2008) and greater as-similation efficiencies of invertebrates than other food items bycrayfish (WhitledgeampRabeni 1997)However the lackof signifi-cantdecreaseintrophicpositiontowardstheinvasionfront intheSouth Fork JDR could be due to a counter-effect from increasingmacroinvertebrate biomass upstream Consumption of macroin-vertebrateshasbeen linkedto increases inweightgainandmeta-bolicrates(BondarBottriellZeronampRichardson2005Hilletal1993 McFeeters Xenopoulos Spooner Wagner amp Frost 2011)Nevertheless in these same studies juvenile signal crayfish in anatural settingdisproportionatelyconsumedfoodtypes thatweretheoppositeofthoseshowntobeofmostnutritionalvaluetothem(Bondar etal 2005) and rusty crayfishmortalitywashigheron adietbasedoninvertebratethanoneonperiphytonordetritus(Hilletal 1993) This suggests that high growth might be associatedwith greater physiological stress due tomore frequentmoultingandhigherforagingcostsinnaturalsettingsThuswehypothesisethatenergyintakeandlong-termfitnessofrustycrayfishassociatedwithperiphytonanddetritusconsumptionmaybehigherthanwithmacroinvertebratedietsdespitetheir lowerdigestionefficiencyoftheseresources
Trade-offs can also arise between increased dispersal rates atrangemarginsand the functional responseof thenon-nativecon-sumer due to the high cost of dispersal (Fronhofer amp Altermatt2015)Giventheircurrentrateofspread(c20kmyeardownstreamfrom2010to2016)intheJDR(MessagerampOlden2018)andawin-dowofactivityof8ndash9months(basedonwatertemperaturesinthemainstem)rustycrayfishwouldhavetoachieveanetdownstreamspreadrateof80mdayonaveragewithoutconsideringtimeded-icatedtomatingandjuvenileparentalcareWespeculatethatthispacecouldrestricttheamountoftimeavailableforactivelypreyingoninvertebratesandcouldselectforthosecrayfishbestabletoef-ficientlyfeedandgrowonabundantandaccessiblebasalresourcesIthasalsobeenhypothesisedforstreamfishesthatthosenon-nativespeciesthatcansustaingrowthandreproductiononlow-qualityre-sourcesshouldbebestabletobecomeestablished(GidoampFranssen2007) Incrayfishabroader trophicniche thatexpandedtowardslower trophic levelsmayhaveaffordedcompetitiveadvantages totheintroducedsignalcrayfishoverthenativenoblecrayfishAstacus astacus inSwedishstreams (OlssonStenrothNystromampGraneli2009) Therefore our findings that rusty crayfish at the invasionfrontactmostlyasprimaryconsumerswhileachievinggreaterphys-iologicalconditionmightreflectanincreaseinfeedingefficiencyonbasal resources as a by-product of greater dispersal ability devel-opedthroughtheirrangeexpansionintheJDR
a crucial first step towards developing spatially explicit strategiestocontrol this invasion If thedocumentedphenotypicshifts fromcore to invasion front populations are indeed associatedwith theaccelerating rateof spreadof rusty crayfish then targeting thoseindividualsattheinvasionleadingedgeforremoval(egbytrapping)mightconstraintheaccumulationofdispersivephenotypesintheseareasAccountingforthesephenotypicshiftsinmechanisticmodelsofinvasivespread(egMessagerampOlden2018)couldalsoprovideuswithavirtual laboratorytotesttheeffectivenessofalternativecontrolstrategiesincontainingthespreadofriverineinvaderssuchasrustycrayfish
Our results suggest that low conspecific densities and spatialsortinginleading-edgepopulationsledtoashift inthephenotypeofrustycrayfishtowards lowercompetitiveabilityhigher intrinsicgrowthandorreproductionandgreaterforagingefficiencyonbasalresourcesastheyspreadupstreamanddownstreamintheJDROurstudydesignenabledustolinkmorphologicalandfunctionaltraitstobetterexploretheconsequencesofthisrangeexpansiononinvadedecosystemsWeexpectthatthediminishedcompetitiveabilityob-servedinthevanguardofthisrustycrayfishinvasionmightleadtoreducedfitnessoftheinvasionfrontphenotypesoncedensities innewlycolonisedareas limit theavailabilityofshelterand intensifycompetition formatesThe long-termevolutionary implicationsofthesephenotypicshiftsmightthusbelimited(PerkinsBoettigerampPhillips2016)Howeverthetrophicshiftobservedininvasionfrontpopulationscouldalsoallowrustycrayfishtoreachhigherdensitiesintheseareasastheymightexploitresourcesmorebroadlyandeffi-cientlyundercompetitiveconditionsTheevolutionaryforcesatplayinthisinvasionhaveprobablyinteractedwithlongitudinalgradientsinenvironmentalconditionsinwaysanalogoustothoseexperiencedbyspeciesduringtheirmigrationtowardscoolerareasunderclimatechangeIntegratingthestudyofmorphologicalandfunctionaltraitswith spatial variation in environmental conditions thus provides arobustwaytoassesswhethercontemporaryevolutionisalteringthephenotypeandecosystemimpactsofspeciesastheirrangeexpandsthroughthelandscape
Inconclusionthisstudyaddsevidenceinsupportofphenotypicchangesexpectedinnon-nativeorganismsexposedtochangingse-lectionpressuresas they invadenewenvironmentsDisentanglingthe causes of these changes whether related to environmentalfactorsorselectionduetorangeexpansionremainsan importantareaofinvestigationasweseektobetterunderstandtheecologicalimpactsofinvasivespeciesandhownativespecieswillrespondtoshiftingenvironmentalconditionsinthefuture
ACKNOWLEDG MENTS
WethankJeffAdamsEricLarsonDavidWoosterStephenBollensandKeithSorensonforprovidinghistoricaldataforrustycrayfishthe staff at theGrantCountyAssessorsoffice and the JohnDayFossilBedsNationalMonument for their help accessing the riverParticular appreciation goes to all the landowners throughout theJohnDayRiverbasin foraccess to their landandsupport for this
12emsp |emsp emspensp MESSAGER And OLdEn
projectWearegratefultoJacobCrunkforhisinestimablehelpwithfieldworkandEthenWhattamforhishelpprocessingmacroinver-tebratesamplesFromtheUniversityofWashingtonwethanktheMolecularEcologyResearchLaboratory(MERLab)andmorespecifi-callyIsadoraJimenez-HidalgoandNatalieLowelltheOldenlabaswellasJoshuaLawlerThomasQuinnandPatrickTobinThemanu-scriptwasimprovedbythecommentsfromtwoanonymousreview-ersFundingsupportwasprovidedbytheJohnNCobbScholarshipin Fisheries the Simpson Award from the Society for FreshwaterScienceandtheCrustaceanSocietyfellowshipinGraduateStudiesawarded to MLM and the University of Washington H MasonKeelerEndowedProfessorshipawardtoJDO
Mathis L Messager httpsorcidorg0000-0002-3051-8068
Julian D Olden httpsorcidorg0000-0003-2143-1187
R E FE R E N C E S
AndersonCampCabanaG (2007)Estimatingthetrophicpositionofaquatic consumers in river food webs using stable nitrogen iso-topes Journal of the North American Benthological Society 26(2)273ndash285 httpsdoiorg1018990887-3593(2007)26[273ettpoa]20co2
Arrington D A ampWinemiller K O (2002) Preservation effects onstable isotope analysis of fishmuscleTransactions of the American Fisheries Society131(2)337ndash342httpsdoiorg1015771548-8659(2002)131lt0337peosiagt20co2
Berdalet E Roldaacuten C ampOlivarM P (2005) Quantifying RNA andDNAinplanktonicorganismswithSYBRGreenIIandnucleasesPartBQuantification in natural samplesScientia Marina69(1) 17ndash30httpsdoiorg103989scimar200569n117
BerdaletERoldaacutenCOlivarMPampLysnesK (2005)QuantifyingRNAandDNAinplanktonicorganismswithSYBRGreenIIandnu-cleases Part A Optimisation of the assay Scientia Marina 69(1)1ndash16httpsdoiorg103989scimar200569n11
Bobeldyk A M amp Lamberti G A (2010) Stream food web re-sponses to a large omnivorous invader Orconectes rusticus (Decapoda Cambaridae) Crustaceana 83(6) 641ndash657 httpsdoiorg101163001121610x491031
BondarCABottriellKZeronKampRichardsonJS(2005)Doestro-phicpositionof theomnivoroussignalcrayfish (Pacifastacus lenius-culus) inastreamfoodwebvarywith lifehistorystageordensityCanadian Journal of Fisheries and Aquatic Sciences62(11)2632ndash2639httpsdoiorg101139f05-167
BrandnerJCerwenkaAFSchliewenUKampGeistJ(2013)BiggerisbetterCharacteristicsofroundgobiesforminganinvasionfrontinthe Danube River PLoS ONE8(9)e73036httpsdoiorg101371journalpone0073036
BrownGPKelehearCampShineR (2013)Theearly toadgets theworm Cane toads at an invasion front benefit from higher preyavailability Journal of Animal Ecology 82(4) 854ndash862 httpsdoiorg1011111365-265612048
Burton O J Phillips B L amp Travis J M J (2010) Trade-offs and the evolution of life-histories during range ex-pansion Ecology Letters 13(10) 1210ndash1220 httpsdoiorg101111j1461-0248201001505x
Capelli G M amp Hamilton P A (1984) Effects of food shelter andtimeof dayon aggressive activity in the crayfishOrconectes rusti-cus(Girard)Journal of Crustacean Biology4(2)252ndash260httpsdoiorg1011631937240x84x00363
Caplat P Cheptou P O Diez J Guisan A Larson B MMacDougall A S hellip Zhang R (2013) Movement impacts andmanagement of plant distributions in response to climate changeInsights from invasions Oikos 122(9) 1265ndash1274 httpsdoiorg101111j1600-0706201300430x
Chuang A amp Peterson C R (2016) Expanding population edgesTheories traits and trade-offsGlobal Change Biology22(2) 494ndash512httpsdoiorg101111gcb13107
ClarkJMKershnerMWampHolomuzkiJR(2008)Grainsizeandsorting effects on size-dependent responses by lotic crayfish tohigh flows Hydrobiologia 610 55ndash66 httpsdoiorg101007s10750-008-9422-0
CrandallKAampDeGraveS (2017)Anupdatedclassificationofthefreshwater crayfishes (Decapoda Astacidea) of the world with acompletespecieslistJournal of Crustacean Biology37(5)615ndash653httpsdoiorg101093jcbiolrux070
DavidsonAMJennionsMampNicotraAB(2011)Doinvasivespe-cies show higher phenotypic plasticity than native species and ifso is it adaptiveAmeta-analysisEcology Letters14(4) 419ndash431httpsdoiorg101111j1461-0248201101596x
DoddsWK Smith VH amp Lohman K (2002)Nitrogen and phos-phorusrelationshipstobenthicalgalbiomassintemperatestreamsCanadian Journal of Fisheries and Aquatic Sciences 59(5) 865ndash874httpsdoiorg101139f02-063
Fronhofer E A amp Altermatt F (2015) Eco-evolutionary feedbacksduring experimental range expansions Nature Communications 66844httpsdoiorg101038ncomms7844
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
6emsp |emsp emspensp MESSAGER And OLdEn
Environmentalconditionsandthespeedofrustycrayfishspreaddiffered among tributaries so each invasion leading edge wasanalysedseparately Intotalfour leading-edgepopulationswereanalysedonedownstreamedge in themainstemJDRand threeupstream edgesmdashin the mainstem South Fork and North ForkJDR(Figure1)
Sixtraitswereanalysedthroughouttheinvasionextentofrustycrayfish carapace length chela length weight trophic positionphysiologicalconditionandsexratio(theproportionofmalesatasite)Onlydataforcrayfishcaughtbykick-seininghand-nettingandsnorkellingwereincludedintheanalysisduetotheknownsizeandsexbiasoftrappingforlargemales(LarsonampOlden2016)Tocon-trolforthestrongrelationshipbetweenbodysizecrayfishweightandchelalengthduetoallometricgrowthresidualsfromcarapacelength-weightandcarapace length-chela lengthnon-linear regres-sionmodels developed separately for each sexwere used as re-sponsevariablesinthemodels(hereafterrelative weight and relative chela length)
A subset of the variablesmeasured at each site was selectedas potential environmental predictors of crayfish trait values theestimatednumberofdegreedays fromAugust2015 toJuly2016(degC)macroinvertebrate AFDW (mg) and chlorophyll a concentra-tion frombenthicgreenalgaeanddiatoms (μgChl-acm2)Degreedayswerecomputedbasedonwater temperatureestimated froma multiple regression model using satellite-measured daily land-surfacetemperaturecalendardaycatchmentareaandelevationaspredictorvariables (MessagerampOlden2018) In situ temperaturemeasurementswere not used in this analysis as diel temperaturevariationswereofthesameorderofmagnitudeasdifferencesbe-tween upstream and downstream sites Velocity and depth mea-surementswerenotincludedintheanalysiseitherduetotheirhighspatialvariabilityatbaseflowintheJDROnlythesitesforwhichallvariableshadbeenmeasuredwereincludedintheanalysisforatotalof18sites14sitesinthemainstemJDRtwointheSouthForkJDRandtwointheNorthForkJDR
In the South Fork andNorth Fork JDRwhere tissue samplesweretakenfromcrayfishinonlytwositesdifferencesintraitvaluesamongsiteswere testedusing two-sample t-testsanddifferencesinsexratiowereassessedwithYatesχ2testInthemainstemJDRgeneralisedadditivemodels(GAMs)weredevelopedtoanalysethedrivers of crayfish morphology physiological condition and tro-phicpositionGAMswerebuiltseparatelyfortwomaincategoriesofpredictorvariablesAfirstcategoryofmodelswasdevelopedtoaccountfortheroleoftherangeexpansionprocessindrivingphe-notypicchangesbyusingeachsitesdistancefromtheinitiallocationofrustycrayfishintroductionasthepredictorvariableThesecondmodel categorywas based on environmental variables thatmightinfluence trait valuesAdditionalmodelswerealsobuiltusingdis-tance from the initial introduction location togetherwith crayfishdensityandsex ratioaspredictorvariablesorcombiningmultipleenvironmentalvariablesThesignificanceandfitofcandidatemod-els(Akaikeinformationcriterionthep-valueofthecoefficientsandtheadjustedR2seeSupportingInformationTableS32)werethen
31emsp|emspCrayfish distribution and habitat conditions
Intotal1266crayfishwerecapturedacrossthe18sitesanalysedin thisstudyofwhich299weresampledformorphological traits259 forphysiological condition and254 for trophicpositionOursurveycombinedwithhistoricaldistributionrecordsandamodelofrustycrayfishspreadintheJDR(MessagerampOlden2018)showedthatrustycrayfishspreadatanacceleratingratesinceitsintroduc-tion and occupied at least 705km of river across the JDR catch-ment inAugust2016Bythatsummer ithadspreadnearly30kmupstreamintheNorthForkandSouthForkJDRandcolonisedthemainstem along a 250km stretch downstream of its introductionpoint(Figure1)Incontrasttoitsextensivespreaddownstreamtheupstreamspreadofrustycrayfishinthemainstemhadbeentempo-rarilyhaltedatthetimeofthesurveyduetoalow-headdam12kmupstream of the putative site of crayfish introduction Densitiesdownstream of the dam were similar to those found at the coreoftheir rangeTherefore theupstreammainsteminvasion leadingedgewasnotincludedinthisanalysisInadditionthepreciseloca-tionofthedownstreammainstemleadingedgecouldnotbedeter-minedduetolimitedaccesstotheriverthusthedownstream-mostsurveyedsitewhererustycrayfishwasfoundinthemainstemwastreatedasthedownstreamedgeoftheirrangeinthisstudy
There was a consistent decrease in rusty crayfish densitiesamongthesampledtributariesfromtheirinitiallocationofintroduc-tiontotheir invasionfrontsRustycrayfishdensities (measuredaskick-seiningcatchperuniteffortFigure2)werehighestinboththemainstem and South Fork JDR (gt30crayfishm2) 40ndash75kmdown-streamoftheinitialsiteofrustycrayfishestablishmentbutrapidlydroppedbyanorderofmagnitudebeyond60kmintheSouthForkJDRandbeyond80kminthemainstemandNorthForkJDRNativesignalcrayfishwerefoundinsympatrywithrustycrayfishinonlyafewsitesattheupstreaminvasionfrontswhererustycrayfishwerefound at lower densities (in the South Forkmainstem and othersmaller side tributaries of the JDR)Where native signal crayfishwerepresent theyoccurredatvery lowdensities (lt2crayfishm2) including in sites without rusty crayfish These findings togetherwithpastrecords (2013)ofsignalcrayfishoccurrence insympatrywithrustycrayfishatsiteswheresignalcrayfishwereabsentduringour2016surveysuggestthatsignalcrayfishisrapidlyexcludedfromsites invadedbyrustycrayfishas itspreadsacrosstheJDRcatch-mentThereforeinterspecificcompetitionwasnotconsideredasig-nificantmechanisminfluencingthetraitsinvestigatedinthisstudy
Temperature and macroinvertebrate biomass followed similarlongitudinalgradients fromupstreamtodownstreambetweenthemainstemSouthFork andNorthFork JDRwhereasbenthicbio-massofgreenalgaeanddiatomwerehighlyvariableamongtribu-taries (Supporting InformationFigureS21)Degreedays increased
emspensp emsp | emsp7MESSAGER And OLdEn
monotonically downstream while macroinvertebrate biomass de-creaseddownstreamTherewasalsoconsiderablevariabilityinmac-roinvertebrate biomass among adjacent sites including a suddenincreaseinbiomassdownstreamfromtheconfluenceofthemain-stemandtheNorthForkJDRwherelowcrayfishdensitiesprevailedGreenalgaeweresparsetoabsentinalltributariesThebiomassofdiatomsontheotherhandwashighestintheSouthForkandupper
mainstemJDR(upto45μgChl-acm2) and low in the lower main-stemandNorthForkJDRwith inconsistent longitudinalgradientsamongtributaries
32emsp|emspMorphology
Therewereconsistenttrendsinrustycrayfishmorphologyfromcore to leading-edge populations in all tributaries (Figure 4SupportingInformationAppendixS3)Therelativechelalengthof rusty crayfish in leading-edge populationswas significantlysmaller than those behind the front in all three tributaries(Mainstem GAM p=003 R2-adjusted=028 n=14 NorthFork t=217 df=29 p=004 South Fork t=303 df=42plt001 Figures3 and 4 Supporting Information TablesS31and S32) Crayfish density was also strongly and positivelyassociatedwith chela length across the JDR (MainstemGAMp=001 R2-adjusted=037 n=14 Figure4 SupportingInformation TableS32) No consistent difference was foundin mean carapace length between core and invasion frontpopulations of the JDR or betweenmale and female crayfishhowever there was a consistent decrease in carapace lengthvariance in thedirectionof the invasion inbothupstreamanddownstream dispersing populations (Figure4 SupportingInformationAppendixS3)Crayfishrelativeweightsignificantlydecreased towards the invasion front both downstream in themainstem (GAM p=004 R2-adjusted=025 n=14) and up-stream in the North Fork (W=177 p=001) and South Fork(W=328 p=001 Supporting Information FigureS41) alongwith decreasing crayfish density (Mainstem GAM p=002R2-adjusted=033 n=14 Figure4 Supporting InformationTableS32)Lastlytherewasnosignificanttrendinthepropor-tionofmalestowardsthefrontsoftheinvasiondespiteaslightincrease inmaledominance inbothupstreamanddownstreamleading edges when considering all sites where gt10 crayfishwerecaptured(SupportingInformationFigureS42)
EnvironmentalconditionswerenotstrongpredictorsofcrayfishmorphologythroughouttheirinvasiongradientDegreedaysdidnotcorrelateconsistentlyacross invasion frontswithanymorphologi-cal trait values (Figure4 Supporting Information TableS32) Forinstancewhiledecreasingupstream temperatureswerepositivelycorrelatedtorelativeweightintheSouthForkandNorthForkJDRtemperatureand relativeweightwerenegativelycorrelated in themainstemSimilarly inconsistentpatternswereobservedbetweentemperature and both relative chela length and carapace lengthMacroinvertebrate biomass (AFDW) was negatively but not sig-nificantly correlated with relative chela length and weight acrosstributariesandwasnotconsistentlyorsignificantlyassociatedwithshifts in carapace length across tributaries (Figure4 SupportingInformationTablesS31andS32)Finallywhilegreenalgaebiomasswasnotconsistentlycorrelatedwithanymorphologicaltraitvaluesdiatombiomasswaspositivelycorrelatedwithrelativechelalengthandweight throughout the JDR (Figure4 Supporting InformationTable S32)
F IGURE 3emspChangesinmeancrayfishrelativechelalength(a)trophicposition(b)andphysiologicalcondition(cRNADNAratioexpressingpotentialforsomaticgrowthandgameteproduction)alongtheinvasiongradientofrustycrayfishintheJohnDayRivercatchmentThesmoothsolidlineandshadedregionrepresentthepredictedmeantraitvalueand95Bayesiancredibleintervalrespectivelyfromageneralisedadditivemodelandasterisksdenotesignificantdifferencesinmean(ple001ple005)VerticaldashedlinesrepresenttheconfluencesoftheSouthFork(at44km)andNorthFork(at87km)withthemainstemJohnDayRiver
8emsp |emsp emspensp MESSAGER And OLdEn
33emsp|emspTrophic position
Thetrophicpositionofrustycrayfishwasconsistentlylowerforin-dividualsat invasion fronts than inpopulationscloser to thecoredespite wide variations among sites throughout the catchment
(Figures3band4SupportingInformationAppendixS3)Inthemain-stemrustycrayfishdietfirstincreaseddownstreamfromthattypi-calofasecondaryconsumeroromnivore(trophicpositionofc 3) to thatofatopcarnivore(trophicpositionofc4)andthendecreasedtowardsthefrontoftheinvasiondowntothatofaprimaryconsumer
F IGURE 4emspSummary of the relationshipsbetweenrustycrayfishtraitsandpredictorvariablesintheJohnDayRiver The direction and colour of the arrowsindicatethesignoftherelationship(egredupwardarrowsreflectpositiverelationships)betweenthepredictorvariable(columns)andthetrait(rows)foragiveninvasionleadingedge(downstreammainstemupstreamSouthForkorupstreamNorthFork)Greyarrowsshowstatisticallynon-significantrelationshipsSignificanceandaconsistentdirectionintherelationshipbetweencandidatepredictorsandtraitsamongtributariessuggestedtheprimacyofthatpredictorindrivingobserveddifferencesintraitsSeeSupportingInformationAppendixS3fordetailedstatisticalresultsFlatgreenarrowsshowvariablesforwhichtherewasnodifferenceamongsitesinthattributaryandrelationshipsdenotedbyandashwerenottestedduetoalackofhypothesisedmechanismsrelatingthevariablesdaggerAsh-freedryweight
Response variable Edge
Predictor variableDistance
from introduction
Crayfish density
Degree days
Macroinv AFDWdagger
Green algae Diatom
Relative chela length
Mainstem
South Fork
North Fork
Trophic position
Mainstem
South Fork
North Fork
Physiological Condition
(RNADNA)
Mainstem
South Fork
North Fork
Carapace length
Mainstem
South Fork
North Fork
Relative weight
Mainstem
South Fork
North Fork
Sex ratio( males)
Mainstemndash ndash ndash ndash ndash
South Forkndash ndash ndash ndash ndash
North Forkndash ndash ndash ndash ndash
Carapace length SD
Mainstemndash ndash ndash ndash
South Forkndash ndash ndash ndash
North Forkndash ndash ndash ndash
daggerAsh-free dry weight
emspensp emsp | emsp9MESSAGER And OLdEn
(trophicpositionofc2GAMp=005R2-adjusted=044n = 14 Figure3b) Therewas an equivalent drop in crayfish trophic posi-tionintheNorthForkJDRupstreamleadingedge(t=966df=22plt0001)butnoequivalentdecreaseintheSouthForkJDRleadingedgeTherewasnodifferenceintrophicpositionamongmaleandfemalecrayfishandalthoughtrophicpositionwasweaklycorrelatedwithcarapacelengthwithinsites(carapacelengthfixedeffect95CI=80times10minus3to19times10minus2trophiclevelmminlinearmixedeffectmodelwithsiteasrandomeffect)therewasnosignificantcorrela-tionbetweentrophicpositionandmeancarapacelengthacrosssitesalongthemainstemTrophicpositionwasnotsignificantlycorrelatedwithrelativechelalengthwithinsites(relativechelalengthfixedef-fect 95 CI=minus83times10minus3 to 23times10minus2 trophic levelmm in linearmixedeffectmodelwithsiteasrandomeffect)
Temperature increasing with downstream distance from theinvasionsourcewascorrelatedwithtrophicpositiononlytowardstheupstreaminvasionfrontsintheNorthForkandSouthForkJDR(Figure4Supporting InformationAppendicesS2andS3)Noneoftheotherenvironmentalvariablessignificantlycovariedwithtrophicpositioninaconsistentwayacrosstributaries(Figure4SupportingInformationAppendicesS2andS3)
34emsp|emspGrowth and condition
There was a consistent positive trend in rusty crayfish physi-ological condition (RNADNA ratio) towards invasion fronts alongwith decreasing crayfish densities (Figures3c and 4 SupportingInformationAppendixS3)Strongesttowardstheupstreamleadingedgesdespitedecreasing temperature (t-test SouthForkW=46p-value=001North Fork t=minus491df=155plt0001) the in-creaseinphysiologicalconditionwasonlymarginalinthemainstem[GAMp=019R2-adjusted=006n=14meanslope=63times10minus3 (95CI=minus27times10minus3to15times10minus2) [RNADNA]km]Thenegativecorrelation between crayfish physiological condition (RNADNAratio)andcrayfishdensityinthemainstemwasalsonon-significant(GAM p=043 R2-adjusted=minus003 n=14) Lastly environmen-tal variables (abiotic and biotic)were not consistently and signifi-cantlyassociatedwithRNADNAratioacrosstributaries(Figure4SupportingInformationAppendixS3)
4emsp |emspDISCUSSION
Thisstudyrevealedsignificanttrendsinmorphologicaltraitvaluesphysiologicalconditionandtrophicpositionofrustycrayfishfromtheirlocationofinitialintroductiontomultipleleadingedgesofinva-sionintheonlyknownpopulationofthisspeciesinwesternNorthAmericaEventhoughthesetrendswerenotconsistentlysignificantacrosstributariestheysuggestthatrustycrayfishindividualsatthevanguard of the invasion exhibited less competitive morphology(decreasedrelativeweightandchelalength)andexploitedenergeticpathwaysloweronthefoodchainyetwereinbetterphysiologicalcondition than individuals located closer to the invasion coreWe
contendthatthesephenotypicshiftsobservedinrustycrayfishareprobablydue to the rangeexpansionprocess itself rather than tonovelenvironmentalconditionsattheirrangeboundariesandthatthesetrendsmayintensifyastheinvasioncontinuestounfoldup-stream and downstream towards the main stem of the ColumbiaRiver
The observed decrease in crayfish relative chela length andweighttowardstheinvasionfrontscanbeattributedtothreemainreasonsmdashalthough further research is needed to confirm the re-spectivecontributionifanyofeachofthesemechanismsFirsttherangeexpansionofrustycrayfishmightbedrivenbytheexclusionof subdominant individuals from high-density population centresthereforeleadingtothewidespreadpresenceofcompetitivelyinfe-riorcrayfishattheinvasionleadingedge(HudinaHockampZganec2014)Inotherwordsindividualcrayfishwithlesscompetitivephe-notypesmayhavebeenforcedoutandsystematically interbredatthe invasionfront resulting in theaccumulationof relatively lightsmall-clawedindividualsattheleadingedgeInsupportofthismech-anismsignalcrayfishattheboundaryoftheirinvasionrangeacrossCroatiadisplaylowerlevelsofaggressionandoftenloseagonisticin-teractionstoindividualsfromtheinvasioncoredespitebeinginbet-ter physical condition (Hudinaetal 2015)However a significantincreaseinrelativeclawsizeawayfromsourcepopulationwasalsoobservedininvasivesignalcrayfishmalesoftheMuraRiverCroatia(Hudinaetal2012)Secondlargerchelaeandastouterbodyshapemay be associated with weaker dispersal ability and thus be se-lectedagainstthroughassociativematingofthefastestdispersersclusteredattheinvasionleadingedgeCrayfishwithshorterchelaeandmorefusiformbodyarebetterabletowithstandhighwaterve-locitiesassuggestedbymorphologicdifferencesbetweencrayfishfound in high-velocity streams compared to those in low-velocitystreams and lakes (Perry etal 2013) Becausewater velocities inexcessof03ndash05msleadtodecreasedcrayfishmovementandpo-tentially increasedenergyexpenditureincrayfish(ClarkKershnerampHolomuzki 2008Matheramp Stein 1993 Perryamp Jones 2017)individualswithshorterchelaeandmorefusiformbodiesmaythusbeabletodisperseforlongerperiodsoftheyearintheJDRwhosedischarge isunregulatedbydamsandflowregimeischaracterisedbyspringsnowmeltThirdlowrustycrayfishconspecificdensitiesat invasion front sitesmay relax the constraints imposedby com-petitioninhigh-densityareasandthusreducetherequirementforinvestment in traitsassociatedwithcompetitionShelterandfoodlimitationsarethemaindriversofagonisticinteractionsincrayfish(BergmanampMoore2003CapelliampHamilton1984)Whentheseresourcesareplentiful inpioneerpopulationsbehaviouralpheno-typesassociatedwithlargeclawsandweightaspartofanaggressionsyndrome(Hudinaetal2012)couldthereforeleadtounnecessaryenergyexpensesand reduced foraging leading to reduced fitness(SihCoteEvansFogartyampPruitt2012)Thusashiftinselectivepressuremayhave led toachange in rustycrayfish lifehistoryattheedgeoftheinvasion involvingthereallocationofenergyfromallometricgrowthofcompetitivetraitstoreproductionanddisper-saltraitsnotmeasuredhere(egwalkingleglength)(Phillipsetal
Weconjecturethatashift intheselectionregimeexperiencedbyrustycrayfishfromcoretoleading-edgeareasisthemostprob-ableexplanationforthetrends inrelativechela lengthandweightobservedinthisstudyHoweverwithoutknowledgeoftheheritabil-ityofthecrayfishtraitsexaminedinthisstudyinferenceregardingthespecificmechanisms inoperation isstill limitedTheaccelerat-ingrateofspreadofrustycrayfish intheJDRthe lowpopulationdensities observedwithin several kilometres of the upstream anddownstreaminvasionfrontsandhighphysiologicalfitnessininva-sionfrontpopulationssuggestthatapushedinvasionexcludingsub-dominantcrayfishfromhigherdensityareasisunlikelytoexplaintheobservedtraitdifferencesMoreoverthereislittletonoevidenceoftheinfluenceofchelasizeorrelativebodyweightondispersalspeed(KamranampMoore 2015) Lastly the difference in relativeweightandchelalengthbetweeninvasioncoreandfrontpopulationscouldalsobedrivenbynaturalselectioninhighcrayfishdensitycorepop-ulationsHistoricaldatafromSorenson(2012)combinedwiththisstudy shownodifference inchela length (Supporting InformationFigureS51)butasignificantincreaseinrelativeweightfrom2010to2016atthepresumedsiteofrustycrayfishintroduction(SupportingInformationFigureS52)Thechangesintraitvaluesobservedherearethuslikelytobetheresultsofacombinationofdriversincludingreducedfitnessofcompetitivephenotypesatlowcrayfishdensityselectionforhighrelativeweightinthepopulationcoreandtrade-offsbetweenthesecompetitiveattributesandother traitsassoci-atedwithhigherdispersalability
Theobserved increase in rustycrayfishanabolicactivitymea-suredasRNADNAinleading-edgepopulationsoftheJDRalthoughweak in themainstem indicates that the rangeexpansionprocesshas led to greater somatic growth andor reproductive potentialin pioneer individuals This pattern matches several documentedincreases inbodyconditiongrowthandreproductivepotential insimilarstreaminvasionsbothwithinasingleinvasiongradientandbetweennativeandnon-nativepopulationsWithintheirnon-nativerange invasion front signal crayfish in Croatia and female spiny-cheekcrayfish in theDanubebothdisplayedgreater reproductivepotentials than their counterparts in core areas with the formeralsobeinginbetterconditionandenergeticstatus(Pacircrvulescuetal2015Rebrinaetal2015)Whencomparingnativeandnon-nativepopulationsofrustycrayfishbothlakeandmesocosmexperimentsfoundthatnon-nativeindividualshavehighergrowthratesandlevelsofactivitythantheirnativecongeners(PintorampSih2009Sargentamp Lodge 2014) Nonetheless whether the observed increase inrustycrayfishphysiologicalconditiontowardstheinvasionfront isassociated with greater somatic growth rates or gamete produc-tionremainsunresolvedandwarrantsfurtherinvestigationIndeed
simultaneous increases inconditiongrowthandreproductivepo-tentialarenotuniversalbecauseselectionfordispersalabilityduringrangeexpansionmay lead tounexpected trade-offsFor instancetadpolesandjuvenilesininvasionfrontpopulationsofcanetoadsintropicalAustraliagrowupto31fasterthanthosefromlongeres-tablishedpopulations(Phillips2009)andadultsdemonstratehigherfeeding rates larger fat stores andbetter condition thanconspe-cifics in later invasion stages (Brownetal2013)However lowerreproductiverateshavealsobeendocumentedincanetoadinvasionfrontpopulations(HudsonPhillipsBrownampShine2015)
Itmightseemthathighercrayfishgrowthratestowardstheinva-sionfrontscontradicttheobservedpatternsofreducedweightandchelalengthobservedinpioneercrayfishHoweverselectionforafasterlifestylecoulddecreaseageatmaturityandshortenthelifes-panoftheseinvasionfrontcrayfishwhileselectingagainstallome-tricgrowthofcompetitivemorphologyBothcrayfishgrowth rateandfecundityaredensitydependent(GuanampWiles1999MomotampGowing1977)Thereforeitispossiblethathighgrowthandfe-cundityphenotypeshavearisenfromnaturalselectioninthec 15 generationssincetheirintroductionaspartofadispersalsyndromeassociating rapid development and high fecunditywith dispersivetraits(RonceampClobert2012Stevensetal2013)
Rustycrayfishattheleadingedgesoftheirdistributionallimitsappeartobefeedinglowerinthefoodwebwhencomparedtocon-specifics locatedbehind the invasion frontThispattern stands incontradictionwithmostpreviousstudiesofstreaminvasionsRoundgobiesattheedgeoftheirexpandingrangeconsumemoreoftheirfavouredpreytypethanincentralpopulations(RabyGutowskyampFox2010)andhavehigherδ15Nsignaturesthanthepreviousyearfront(Brandneretal2013)Invasionfrontbloodyredmysidshrimp(Hemimysis anomala)werenotmoreselectiveintheirpreyconsump-tionbutshowedgreaterabilitytolocateandcapturezooplanktonprey than those shrimp in corepopulations (Iacarella etal 2015)ForcrayfishinvasionstrophicnicheshiftshaveonlybeenassessedatthebiogeographicalscaleandoffermixedinsightsInagreementwithourfindingsnon-nativepopulationsofrustycrayfishandvirilecrayfish(Faxonius virilis)appearedtoshowgreaterratesofalgaecon-sumption (despite constant macroinvertebrate prey consumption)thandidnativepopulationsinlaboratoryassays(Glonetal2018)By contrast an intercontinental stable isotope analysis revealedtrophicnicheconservatisminsignalcrayfishbetweenitsnativeandnon-native range (LarsonOldenampUsio 2010) Trophic flexibilityhasbeenshowntobespecies-dependenteveninsympatricnativecrayfishspecies (JohnstonRobsonampFairweather2011)andmaythus not be a consistent characteristic among invasive omnivoreseitherItisunlikelythatcannibalismawidespreadphenomenonincrayfishpopulations(GuanampWiles1998) ledtotheobservedin-creaseintrophicpositioninareaswithhighdensitiesofcrayfishasconspecificdensitywasnotcorrelatedtotrophicpositionintheJDR(Figure4SupportingInformationAppendixS3)Lastlyitisunlikelythatnon-crayfishpredatorsandcompetitorscouldhavedriventhisdownwardshiftinthetrophicpositionofrustycrayfishasthisshiftwasobservedacrossboththedownstream(increasingfishdensity)
Rustycrayfishhada lower trophicpositionevenwhenmacro-invertebrateprey availability increased towards the invasion frontintheNorthForkJDRThispatterncontrastedwithpastevidenceof a positive relationship between macroinvertebrate availabilityand crayfish trophic position (Olsson etal 2008) and greater as-similation efficiencies of invertebrates than other food items bycrayfish (WhitledgeampRabeni 1997)However the lackof signifi-cantdecreaseintrophicpositiontowardstheinvasionfront intheSouth Fork JDR could be due to a counter-effect from increasingmacroinvertebrate biomass upstream Consumption of macroin-vertebrateshasbeen linkedto increases inweightgainandmeta-bolicrates(BondarBottriellZeronampRichardson2005Hilletal1993 McFeeters Xenopoulos Spooner Wagner amp Frost 2011)Nevertheless in these same studies juvenile signal crayfish in anatural settingdisproportionatelyconsumedfoodtypes thatweretheoppositeofthoseshowntobeofmostnutritionalvaluetothem(Bondar etal 2005) and rusty crayfishmortalitywashigheron adietbasedoninvertebratethanoneonperiphytonordetritus(Hilletal 1993) This suggests that high growth might be associatedwith greater physiological stress due tomore frequentmoultingandhigherforagingcostsinnaturalsettingsThuswehypothesisethatenergyintakeandlong-termfitnessofrustycrayfishassociatedwithperiphytonanddetritusconsumptionmaybehigherthanwithmacroinvertebratedietsdespitetheir lowerdigestionefficiencyoftheseresources
Trade-offs can also arise between increased dispersal rates atrangemarginsand the functional responseof thenon-nativecon-sumer due to the high cost of dispersal (Fronhofer amp Altermatt2015)Giventheircurrentrateofspread(c20kmyeardownstreamfrom2010to2016)intheJDR(MessagerampOlden2018)andawin-dowofactivityof8ndash9months(basedonwatertemperaturesinthemainstem)rustycrayfishwouldhavetoachieveanetdownstreamspreadrateof80mdayonaveragewithoutconsideringtimeded-icatedtomatingandjuvenileparentalcareWespeculatethatthispacecouldrestricttheamountoftimeavailableforactivelypreyingoninvertebratesandcouldselectforthosecrayfishbestabletoef-ficientlyfeedandgrowonabundantandaccessiblebasalresourcesIthasalsobeenhypothesisedforstreamfishesthatthosenon-nativespeciesthatcansustaingrowthandreproductiononlow-qualityre-sourcesshouldbebestabletobecomeestablished(GidoampFranssen2007) Incrayfishabroader trophicniche thatexpandedtowardslower trophic levelsmayhaveaffordedcompetitiveadvantages totheintroducedsignalcrayfishoverthenativenoblecrayfishAstacus astacus inSwedishstreams (OlssonStenrothNystromampGraneli2009) Therefore our findings that rusty crayfish at the invasionfrontactmostlyasprimaryconsumerswhileachievinggreaterphys-iologicalconditionmightreflectanincreaseinfeedingefficiencyonbasal resources as a by-product of greater dispersal ability devel-opedthroughtheirrangeexpansionintheJDR
a crucial first step towards developing spatially explicit strategiestocontrol this invasion If thedocumentedphenotypicshifts fromcore to invasion front populations are indeed associatedwith theaccelerating rateof spreadof rusty crayfish then targeting thoseindividualsattheinvasionleadingedgeforremoval(egbytrapping)mightconstraintheaccumulationofdispersivephenotypesintheseareasAccountingforthesephenotypicshiftsinmechanisticmodelsofinvasivespread(egMessagerampOlden2018)couldalsoprovideuswithavirtual laboratorytotesttheeffectivenessofalternativecontrolstrategiesincontainingthespreadofriverineinvaderssuchasrustycrayfish
Our results suggest that low conspecific densities and spatialsortinginleading-edgepopulationsledtoashift inthephenotypeofrustycrayfishtowards lowercompetitiveabilityhigher intrinsicgrowthandorreproductionandgreaterforagingefficiencyonbasalresourcesastheyspreadupstreamanddownstreamintheJDROurstudydesignenabledustolinkmorphologicalandfunctionaltraitstobetterexploretheconsequencesofthisrangeexpansiononinvadedecosystemsWeexpectthatthediminishedcompetitiveabilityob-servedinthevanguardofthisrustycrayfishinvasionmightleadtoreducedfitnessoftheinvasionfrontphenotypesoncedensities innewlycolonisedareas limit theavailabilityofshelterand intensifycompetition formatesThe long-termevolutionary implicationsofthesephenotypicshiftsmightthusbelimited(PerkinsBoettigerampPhillips2016)Howeverthetrophicshiftobservedininvasionfrontpopulationscouldalsoallowrustycrayfishtoreachhigherdensitiesintheseareasastheymightexploitresourcesmorebroadlyandeffi-cientlyundercompetitiveconditionsTheevolutionaryforcesatplayinthisinvasionhaveprobablyinteractedwithlongitudinalgradientsinenvironmentalconditionsinwaysanalogoustothoseexperiencedbyspeciesduringtheirmigrationtowardscoolerareasunderclimatechangeIntegratingthestudyofmorphologicalandfunctionaltraitswith spatial variation in environmental conditions thus provides arobustwaytoassesswhethercontemporaryevolutionisalteringthephenotypeandecosystemimpactsofspeciesastheirrangeexpandsthroughthelandscape
Inconclusionthisstudyaddsevidenceinsupportofphenotypicchangesexpectedinnon-nativeorganismsexposedtochangingse-lectionpressuresas they invadenewenvironmentsDisentanglingthe causes of these changes whether related to environmentalfactorsorselectionduetorangeexpansionremainsan importantareaofinvestigationasweseektobetterunderstandtheecologicalimpactsofinvasivespeciesandhownativespecieswillrespondtoshiftingenvironmentalconditionsinthefuture
ACKNOWLEDG MENTS
WethankJeffAdamsEricLarsonDavidWoosterStephenBollensandKeithSorensonforprovidinghistoricaldataforrustycrayfishthe staff at theGrantCountyAssessorsoffice and the JohnDayFossilBedsNationalMonument for their help accessing the riverParticular appreciation goes to all the landowners throughout theJohnDayRiverbasin foraccess to their landandsupport for this
12emsp |emsp emspensp MESSAGER And OLdEn
projectWearegratefultoJacobCrunkforhisinestimablehelpwithfieldworkandEthenWhattamforhishelpprocessingmacroinver-tebratesamplesFromtheUniversityofWashingtonwethanktheMolecularEcologyResearchLaboratory(MERLab)andmorespecifi-callyIsadoraJimenez-HidalgoandNatalieLowelltheOldenlabaswellasJoshuaLawlerThomasQuinnandPatrickTobinThemanu-scriptwasimprovedbythecommentsfromtwoanonymousreview-ersFundingsupportwasprovidedbytheJohnNCobbScholarshipin Fisheries the Simpson Award from the Society for FreshwaterScienceandtheCrustaceanSocietyfellowshipinGraduateStudiesawarded to MLM and the University of Washington H MasonKeelerEndowedProfessorshipawardtoJDO
Mathis L Messager httpsorcidorg0000-0002-3051-8068
Julian D Olden httpsorcidorg0000-0003-2143-1187
R E FE R E N C E S
AndersonCampCabanaG (2007)Estimatingthetrophicpositionofaquatic consumers in river food webs using stable nitrogen iso-topes Journal of the North American Benthological Society 26(2)273ndash285 httpsdoiorg1018990887-3593(2007)26[273ettpoa]20co2
Arrington D A ampWinemiller K O (2002) Preservation effects onstable isotope analysis of fishmuscleTransactions of the American Fisheries Society131(2)337ndash342httpsdoiorg1015771548-8659(2002)131lt0337peosiagt20co2
Berdalet E Roldaacuten C ampOlivarM P (2005) Quantifying RNA andDNAinplanktonicorganismswithSYBRGreenIIandnucleasesPartBQuantification in natural samplesScientia Marina69(1) 17ndash30httpsdoiorg103989scimar200569n117
BerdaletERoldaacutenCOlivarMPampLysnesK (2005)QuantifyingRNAandDNAinplanktonicorganismswithSYBRGreenIIandnu-cleases Part A Optimisation of the assay Scientia Marina 69(1)1ndash16httpsdoiorg103989scimar200569n11
Bobeldyk A M amp Lamberti G A (2010) Stream food web re-sponses to a large omnivorous invader Orconectes rusticus (Decapoda Cambaridae) Crustaceana 83(6) 641ndash657 httpsdoiorg101163001121610x491031
BondarCABottriellKZeronKampRichardsonJS(2005)Doestro-phicpositionof theomnivoroussignalcrayfish (Pacifastacus lenius-culus) inastreamfoodwebvarywith lifehistorystageordensityCanadian Journal of Fisheries and Aquatic Sciences62(11)2632ndash2639httpsdoiorg101139f05-167
BrandnerJCerwenkaAFSchliewenUKampGeistJ(2013)BiggerisbetterCharacteristicsofroundgobiesforminganinvasionfrontinthe Danube River PLoS ONE8(9)e73036httpsdoiorg101371journalpone0073036
BrownGPKelehearCampShineR (2013)Theearly toadgets theworm Cane toads at an invasion front benefit from higher preyavailability Journal of Animal Ecology 82(4) 854ndash862 httpsdoiorg1011111365-265612048
Burton O J Phillips B L amp Travis J M J (2010) Trade-offs and the evolution of life-histories during range ex-pansion Ecology Letters 13(10) 1210ndash1220 httpsdoiorg101111j1461-0248201001505x
Capelli G M amp Hamilton P A (1984) Effects of food shelter andtimeof dayon aggressive activity in the crayfishOrconectes rusti-cus(Girard)Journal of Crustacean Biology4(2)252ndash260httpsdoiorg1011631937240x84x00363
Caplat P Cheptou P O Diez J Guisan A Larson B MMacDougall A S hellip Zhang R (2013) Movement impacts andmanagement of plant distributions in response to climate changeInsights from invasions Oikos 122(9) 1265ndash1274 httpsdoiorg101111j1600-0706201300430x
Chuang A amp Peterson C R (2016) Expanding population edgesTheories traits and trade-offsGlobal Change Biology22(2) 494ndash512httpsdoiorg101111gcb13107
ClarkJMKershnerMWampHolomuzkiJR(2008)Grainsizeandsorting effects on size-dependent responses by lotic crayfish tohigh flows Hydrobiologia 610 55ndash66 httpsdoiorg101007s10750-008-9422-0
CrandallKAampDeGraveS (2017)Anupdatedclassificationofthefreshwater crayfishes (Decapoda Astacidea) of the world with acompletespecieslistJournal of Crustacean Biology37(5)615ndash653httpsdoiorg101093jcbiolrux070
DavidsonAMJennionsMampNicotraAB(2011)Doinvasivespe-cies show higher phenotypic plasticity than native species and ifso is it adaptiveAmeta-analysisEcology Letters14(4) 419ndash431httpsdoiorg101111j1461-0248201101596x
DoddsWK Smith VH amp Lohman K (2002)Nitrogen and phos-phorusrelationshipstobenthicalgalbiomassintemperatestreamsCanadian Journal of Fisheries and Aquatic Sciences 59(5) 865ndash874httpsdoiorg101139f02-063
Fronhofer E A amp Altermatt F (2015) Eco-evolutionary feedbacksduring experimental range expansions Nature Communications 66844httpsdoiorg101038ncomms7844
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
emspensp emsp | emsp7MESSAGER And OLdEn
monotonically downstream while macroinvertebrate biomass de-creaseddownstreamTherewasalsoconsiderablevariabilityinmac-roinvertebrate biomass among adjacent sites including a suddenincreaseinbiomassdownstreamfromtheconfluenceofthemain-stemandtheNorthForkJDRwherelowcrayfishdensitiesprevailedGreenalgaeweresparsetoabsentinalltributariesThebiomassofdiatomsontheotherhandwashighestintheSouthForkandupper
mainstemJDR(upto45μgChl-acm2) and low in the lower main-stemandNorthForkJDRwith inconsistent longitudinalgradientsamongtributaries
32emsp|emspMorphology
Therewereconsistenttrendsinrustycrayfishmorphologyfromcore to leading-edge populations in all tributaries (Figure 4SupportingInformationAppendixS3)Therelativechelalengthof rusty crayfish in leading-edge populationswas significantlysmaller than those behind the front in all three tributaries(Mainstem GAM p=003 R2-adjusted=028 n=14 NorthFork t=217 df=29 p=004 South Fork t=303 df=42plt001 Figures3 and 4 Supporting Information TablesS31and S32) Crayfish density was also strongly and positivelyassociatedwith chela length across the JDR (MainstemGAMp=001 R2-adjusted=037 n=14 Figure4 SupportingInformation TableS32) No consistent difference was foundin mean carapace length between core and invasion frontpopulations of the JDR or betweenmale and female crayfishhowever there was a consistent decrease in carapace lengthvariance in thedirectionof the invasion inbothupstreamanddownstream dispersing populations (Figure4 SupportingInformationAppendixS3)Crayfishrelativeweightsignificantlydecreased towards the invasion front both downstream in themainstem (GAM p=004 R2-adjusted=025 n=14) and up-stream in the North Fork (W=177 p=001) and South Fork(W=328 p=001 Supporting Information FigureS41) alongwith decreasing crayfish density (Mainstem GAM p=002R2-adjusted=033 n=14 Figure4 Supporting InformationTableS32)Lastlytherewasnosignificanttrendinthepropor-tionofmalestowardsthefrontsoftheinvasiondespiteaslightincrease inmaledominance inbothupstreamanddownstreamleading edges when considering all sites where gt10 crayfishwerecaptured(SupportingInformationFigureS42)
EnvironmentalconditionswerenotstrongpredictorsofcrayfishmorphologythroughouttheirinvasiongradientDegreedaysdidnotcorrelateconsistentlyacross invasion frontswithanymorphologi-cal trait values (Figure4 Supporting Information TableS32) Forinstancewhiledecreasingupstream temperatureswerepositivelycorrelatedtorelativeweightintheSouthForkandNorthForkJDRtemperatureand relativeweightwerenegativelycorrelated in themainstemSimilarly inconsistentpatternswereobservedbetweentemperature and both relative chela length and carapace lengthMacroinvertebrate biomass (AFDW) was negatively but not sig-nificantly correlated with relative chela length and weight acrosstributariesandwasnotconsistentlyorsignificantlyassociatedwithshifts in carapace length across tributaries (Figure4 SupportingInformationTablesS31andS32)Finallywhilegreenalgaebiomasswasnotconsistentlycorrelatedwithanymorphologicaltraitvaluesdiatombiomasswaspositivelycorrelatedwithrelativechelalengthandweight throughout the JDR (Figure4 Supporting InformationTable S32)
F IGURE 3emspChangesinmeancrayfishrelativechelalength(a)trophicposition(b)andphysiologicalcondition(cRNADNAratioexpressingpotentialforsomaticgrowthandgameteproduction)alongtheinvasiongradientofrustycrayfishintheJohnDayRivercatchmentThesmoothsolidlineandshadedregionrepresentthepredictedmeantraitvalueand95Bayesiancredibleintervalrespectivelyfromageneralisedadditivemodelandasterisksdenotesignificantdifferencesinmean(ple001ple005)VerticaldashedlinesrepresenttheconfluencesoftheSouthFork(at44km)andNorthFork(at87km)withthemainstemJohnDayRiver
8emsp |emsp emspensp MESSAGER And OLdEn
33emsp|emspTrophic position
Thetrophicpositionofrustycrayfishwasconsistentlylowerforin-dividualsat invasion fronts than inpopulationscloser to thecoredespite wide variations among sites throughout the catchment
(Figures3band4SupportingInformationAppendixS3)Inthemain-stemrustycrayfishdietfirstincreaseddownstreamfromthattypi-calofasecondaryconsumeroromnivore(trophicpositionofc 3) to thatofatopcarnivore(trophicpositionofc4)andthendecreasedtowardsthefrontoftheinvasiondowntothatofaprimaryconsumer
F IGURE 4emspSummary of the relationshipsbetweenrustycrayfishtraitsandpredictorvariablesintheJohnDayRiver The direction and colour of the arrowsindicatethesignoftherelationship(egredupwardarrowsreflectpositiverelationships)betweenthepredictorvariable(columns)andthetrait(rows)foragiveninvasionleadingedge(downstreammainstemupstreamSouthForkorupstreamNorthFork)Greyarrowsshowstatisticallynon-significantrelationshipsSignificanceandaconsistentdirectionintherelationshipbetweencandidatepredictorsandtraitsamongtributariessuggestedtheprimacyofthatpredictorindrivingobserveddifferencesintraitsSeeSupportingInformationAppendixS3fordetailedstatisticalresultsFlatgreenarrowsshowvariablesforwhichtherewasnodifferenceamongsitesinthattributaryandrelationshipsdenotedbyandashwerenottestedduetoalackofhypothesisedmechanismsrelatingthevariablesdaggerAsh-freedryweight
Response variable Edge
Predictor variableDistance
from introduction
Crayfish density
Degree days
Macroinv AFDWdagger
Green algae Diatom
Relative chela length
Mainstem
South Fork
North Fork
Trophic position
Mainstem
South Fork
North Fork
Physiological Condition
(RNADNA)
Mainstem
South Fork
North Fork
Carapace length
Mainstem
South Fork
North Fork
Relative weight
Mainstem
South Fork
North Fork
Sex ratio( males)
Mainstemndash ndash ndash ndash ndash
South Forkndash ndash ndash ndash ndash
North Forkndash ndash ndash ndash ndash
Carapace length SD
Mainstemndash ndash ndash ndash
South Forkndash ndash ndash ndash
North Forkndash ndash ndash ndash
daggerAsh-free dry weight
emspensp emsp | emsp9MESSAGER And OLdEn
(trophicpositionofc2GAMp=005R2-adjusted=044n = 14 Figure3b) Therewas an equivalent drop in crayfish trophic posi-tionintheNorthForkJDRupstreamleadingedge(t=966df=22plt0001)butnoequivalentdecreaseintheSouthForkJDRleadingedgeTherewasnodifferenceintrophicpositionamongmaleandfemalecrayfishandalthoughtrophicpositionwasweaklycorrelatedwithcarapacelengthwithinsites(carapacelengthfixedeffect95CI=80times10minus3to19times10minus2trophiclevelmminlinearmixedeffectmodelwithsiteasrandomeffect)therewasnosignificantcorrela-tionbetweentrophicpositionandmeancarapacelengthacrosssitesalongthemainstemTrophicpositionwasnotsignificantlycorrelatedwithrelativechelalengthwithinsites(relativechelalengthfixedef-fect 95 CI=minus83times10minus3 to 23times10minus2 trophic levelmm in linearmixedeffectmodelwithsiteasrandomeffect)
Temperature increasing with downstream distance from theinvasionsourcewascorrelatedwithtrophicpositiononlytowardstheupstreaminvasionfrontsintheNorthForkandSouthForkJDR(Figure4Supporting InformationAppendicesS2andS3)Noneoftheotherenvironmentalvariablessignificantlycovariedwithtrophicpositioninaconsistentwayacrosstributaries(Figure4SupportingInformationAppendicesS2andS3)
34emsp|emspGrowth and condition
There was a consistent positive trend in rusty crayfish physi-ological condition (RNADNA ratio) towards invasion fronts alongwith decreasing crayfish densities (Figures3c and 4 SupportingInformationAppendixS3)Strongesttowardstheupstreamleadingedgesdespitedecreasing temperature (t-test SouthForkW=46p-value=001North Fork t=minus491df=155plt0001) the in-creaseinphysiologicalconditionwasonlymarginalinthemainstem[GAMp=019R2-adjusted=006n=14meanslope=63times10minus3 (95CI=minus27times10minus3to15times10minus2) [RNADNA]km]Thenegativecorrelation between crayfish physiological condition (RNADNAratio)andcrayfishdensityinthemainstemwasalsonon-significant(GAM p=043 R2-adjusted=minus003 n=14) Lastly environmen-tal variables (abiotic and biotic)were not consistently and signifi-cantlyassociatedwithRNADNAratioacrosstributaries(Figure4SupportingInformationAppendixS3)
4emsp |emspDISCUSSION
Thisstudyrevealedsignificanttrendsinmorphologicaltraitvaluesphysiologicalconditionandtrophicpositionofrustycrayfishfromtheirlocationofinitialintroductiontomultipleleadingedgesofinva-sionintheonlyknownpopulationofthisspeciesinwesternNorthAmericaEventhoughthesetrendswerenotconsistentlysignificantacrosstributariestheysuggestthatrustycrayfishindividualsatthevanguard of the invasion exhibited less competitive morphology(decreasedrelativeweightandchelalength)andexploitedenergeticpathwaysloweronthefoodchainyetwereinbetterphysiologicalcondition than individuals located closer to the invasion coreWe
contendthatthesephenotypicshiftsobservedinrustycrayfishareprobablydue to the rangeexpansionprocess itself rather than tonovelenvironmentalconditionsattheirrangeboundariesandthatthesetrendsmayintensifyastheinvasioncontinuestounfoldup-stream and downstream towards the main stem of the ColumbiaRiver
The observed decrease in crayfish relative chela length andweighttowardstheinvasionfrontscanbeattributedtothreemainreasonsmdashalthough further research is needed to confirm the re-spectivecontributionifanyofeachofthesemechanismsFirsttherangeexpansionofrustycrayfishmightbedrivenbytheexclusionof subdominant individuals from high-density population centresthereforeleadingtothewidespreadpresenceofcompetitivelyinfe-riorcrayfishattheinvasionleadingedge(HudinaHockampZganec2014)Inotherwordsindividualcrayfishwithlesscompetitivephe-notypesmayhavebeenforcedoutandsystematically interbredatthe invasionfront resulting in theaccumulationof relatively lightsmall-clawedindividualsattheleadingedgeInsupportofthismech-anismsignalcrayfishattheboundaryoftheirinvasionrangeacrossCroatiadisplaylowerlevelsofaggressionandoftenloseagonisticin-teractionstoindividualsfromtheinvasioncoredespitebeinginbet-ter physical condition (Hudinaetal 2015)However a significantincreaseinrelativeclawsizeawayfromsourcepopulationwasalsoobservedininvasivesignalcrayfishmalesoftheMuraRiverCroatia(Hudinaetal2012)Secondlargerchelaeandastouterbodyshapemay be associated with weaker dispersal ability and thus be se-lectedagainstthroughassociativematingofthefastestdispersersclusteredattheinvasionleadingedgeCrayfishwithshorterchelaeandmorefusiformbodyarebetterabletowithstandhighwaterve-locitiesassuggestedbymorphologicdifferencesbetweencrayfishfound in high-velocity streams compared to those in low-velocitystreams and lakes (Perry etal 2013) Becausewater velocities inexcessof03ndash05msleadtodecreasedcrayfishmovementandpo-tentially increasedenergyexpenditureincrayfish(ClarkKershnerampHolomuzki 2008Matheramp Stein 1993 Perryamp Jones 2017)individualswithshorterchelaeandmorefusiformbodiesmaythusbeabletodisperseforlongerperiodsoftheyearintheJDRwhosedischarge isunregulatedbydamsandflowregimeischaracterisedbyspringsnowmeltThirdlowrustycrayfishconspecificdensitiesat invasion front sitesmay relax the constraints imposedby com-petitioninhigh-densityareasandthusreducetherequirementforinvestment in traitsassociatedwithcompetitionShelterandfoodlimitationsarethemaindriversofagonisticinteractionsincrayfish(BergmanampMoore2003CapelliampHamilton1984)Whentheseresourcesareplentiful inpioneerpopulationsbehaviouralpheno-typesassociatedwithlargeclawsandweightaspartofanaggressionsyndrome(Hudinaetal2012)couldthereforeleadtounnecessaryenergyexpensesand reduced foraging leading to reduced fitness(SihCoteEvansFogartyampPruitt2012)Thusashiftinselectivepressuremayhave led toachange in rustycrayfish lifehistoryattheedgeoftheinvasion involvingthereallocationofenergyfromallometricgrowthofcompetitivetraitstoreproductionanddisper-saltraitsnotmeasuredhere(egwalkingleglength)(Phillipsetal
Weconjecturethatashift intheselectionregimeexperiencedbyrustycrayfishfromcoretoleading-edgeareasisthemostprob-ableexplanationforthetrends inrelativechela lengthandweightobservedinthisstudyHoweverwithoutknowledgeoftheheritabil-ityofthecrayfishtraitsexaminedinthisstudyinferenceregardingthespecificmechanisms inoperation isstill limitedTheaccelerat-ingrateofspreadofrustycrayfish intheJDRthe lowpopulationdensities observedwithin several kilometres of the upstream anddownstreaminvasionfrontsandhighphysiologicalfitnessininva-sionfrontpopulationssuggestthatapushedinvasionexcludingsub-dominantcrayfishfromhigherdensityareasisunlikelytoexplaintheobservedtraitdifferencesMoreoverthereislittletonoevidenceoftheinfluenceofchelasizeorrelativebodyweightondispersalspeed(KamranampMoore 2015) Lastly the difference in relativeweightandchelalengthbetweeninvasioncoreandfrontpopulationscouldalsobedrivenbynaturalselectioninhighcrayfishdensitycorepop-ulationsHistoricaldatafromSorenson(2012)combinedwiththisstudy shownodifference inchela length (Supporting InformationFigureS51)butasignificantincreaseinrelativeweightfrom2010to2016atthepresumedsiteofrustycrayfishintroduction(SupportingInformationFigureS52)Thechangesintraitvaluesobservedherearethuslikelytobetheresultsofacombinationofdriversincludingreducedfitnessofcompetitivephenotypesatlowcrayfishdensityselectionforhighrelativeweightinthepopulationcoreandtrade-offsbetweenthesecompetitiveattributesandother traitsassoci-atedwithhigherdispersalability
Theobserved increase in rustycrayfishanabolicactivitymea-suredasRNADNAinleading-edgepopulationsoftheJDRalthoughweak in themainstem indicates that the rangeexpansionprocesshas led to greater somatic growth andor reproductive potentialin pioneer individuals This pattern matches several documentedincreases inbodyconditiongrowthandreproductivepotential insimilarstreaminvasionsbothwithinasingleinvasiongradientandbetweennativeandnon-nativepopulationsWithintheirnon-nativerange invasion front signal crayfish in Croatia and female spiny-cheekcrayfish in theDanubebothdisplayedgreater reproductivepotentials than their counterparts in core areas with the formeralsobeinginbetterconditionandenergeticstatus(Pacircrvulescuetal2015Rebrinaetal2015)Whencomparingnativeandnon-nativepopulationsofrustycrayfishbothlakeandmesocosmexperimentsfoundthatnon-nativeindividualshavehighergrowthratesandlevelsofactivitythantheirnativecongeners(PintorampSih2009Sargentamp Lodge 2014) Nonetheless whether the observed increase inrustycrayfishphysiologicalconditiontowardstheinvasionfront isassociated with greater somatic growth rates or gamete produc-tionremainsunresolvedandwarrantsfurtherinvestigationIndeed
simultaneous increases inconditiongrowthandreproductivepo-tentialarenotuniversalbecauseselectionfordispersalabilityduringrangeexpansionmay lead tounexpected trade-offsFor instancetadpolesandjuvenilesininvasionfrontpopulationsofcanetoadsintropicalAustraliagrowupto31fasterthanthosefromlongeres-tablishedpopulations(Phillips2009)andadultsdemonstratehigherfeeding rates larger fat stores andbetter condition thanconspe-cifics in later invasion stages (Brownetal2013)However lowerreproductiverateshavealsobeendocumentedincanetoadinvasionfrontpopulations(HudsonPhillipsBrownampShine2015)
Itmightseemthathighercrayfishgrowthratestowardstheinva-sionfrontscontradicttheobservedpatternsofreducedweightandchelalengthobservedinpioneercrayfishHoweverselectionforafasterlifestylecoulddecreaseageatmaturityandshortenthelifes-panoftheseinvasionfrontcrayfishwhileselectingagainstallome-tricgrowthofcompetitivemorphologyBothcrayfishgrowth rateandfecundityaredensitydependent(GuanampWiles1999MomotampGowing1977)Thereforeitispossiblethathighgrowthandfe-cundityphenotypeshavearisenfromnaturalselectioninthec 15 generationssincetheirintroductionaspartofadispersalsyndromeassociating rapid development and high fecunditywith dispersivetraits(RonceampClobert2012Stevensetal2013)
Rustycrayfishattheleadingedgesoftheirdistributionallimitsappeartobefeedinglowerinthefoodwebwhencomparedtocon-specifics locatedbehind the invasion frontThispattern stands incontradictionwithmostpreviousstudiesofstreaminvasionsRoundgobiesattheedgeoftheirexpandingrangeconsumemoreoftheirfavouredpreytypethanincentralpopulations(RabyGutowskyampFox2010)andhavehigherδ15Nsignaturesthanthepreviousyearfront(Brandneretal2013)Invasionfrontbloodyredmysidshrimp(Hemimysis anomala)werenotmoreselectiveintheirpreyconsump-tionbutshowedgreaterabilitytolocateandcapturezooplanktonprey than those shrimp in corepopulations (Iacarella etal 2015)ForcrayfishinvasionstrophicnicheshiftshaveonlybeenassessedatthebiogeographicalscaleandoffermixedinsightsInagreementwithourfindingsnon-nativepopulationsofrustycrayfishandvirilecrayfish(Faxonius virilis)appearedtoshowgreaterratesofalgaecon-sumption (despite constant macroinvertebrate prey consumption)thandidnativepopulationsinlaboratoryassays(Glonetal2018)By contrast an intercontinental stable isotope analysis revealedtrophicnicheconservatisminsignalcrayfishbetweenitsnativeandnon-native range (LarsonOldenampUsio 2010) Trophic flexibilityhasbeenshowntobespecies-dependenteveninsympatricnativecrayfishspecies (JohnstonRobsonampFairweather2011)andmaythus not be a consistent characteristic among invasive omnivoreseitherItisunlikelythatcannibalismawidespreadphenomenonincrayfishpopulations(GuanampWiles1998) ledtotheobservedin-creaseintrophicpositioninareaswithhighdensitiesofcrayfishasconspecificdensitywasnotcorrelatedtotrophicpositionintheJDR(Figure4SupportingInformationAppendixS3)Lastlyitisunlikelythatnon-crayfishpredatorsandcompetitorscouldhavedriventhisdownwardshiftinthetrophicpositionofrustycrayfishasthisshiftwasobservedacrossboththedownstream(increasingfishdensity)
Rustycrayfishhada lower trophicpositionevenwhenmacro-invertebrateprey availability increased towards the invasion frontintheNorthForkJDRThispatterncontrastedwithpastevidenceof a positive relationship between macroinvertebrate availabilityand crayfish trophic position (Olsson etal 2008) and greater as-similation efficiencies of invertebrates than other food items bycrayfish (WhitledgeampRabeni 1997)However the lackof signifi-cantdecreaseintrophicpositiontowardstheinvasionfront intheSouth Fork JDR could be due to a counter-effect from increasingmacroinvertebrate biomass upstream Consumption of macroin-vertebrateshasbeen linkedto increases inweightgainandmeta-bolicrates(BondarBottriellZeronampRichardson2005Hilletal1993 McFeeters Xenopoulos Spooner Wagner amp Frost 2011)Nevertheless in these same studies juvenile signal crayfish in anatural settingdisproportionatelyconsumedfoodtypes thatweretheoppositeofthoseshowntobeofmostnutritionalvaluetothem(Bondar etal 2005) and rusty crayfishmortalitywashigheron adietbasedoninvertebratethanoneonperiphytonordetritus(Hilletal 1993) This suggests that high growth might be associatedwith greater physiological stress due tomore frequentmoultingandhigherforagingcostsinnaturalsettingsThuswehypothesisethatenergyintakeandlong-termfitnessofrustycrayfishassociatedwithperiphytonanddetritusconsumptionmaybehigherthanwithmacroinvertebratedietsdespitetheir lowerdigestionefficiencyoftheseresources
Trade-offs can also arise between increased dispersal rates atrangemarginsand the functional responseof thenon-nativecon-sumer due to the high cost of dispersal (Fronhofer amp Altermatt2015)Giventheircurrentrateofspread(c20kmyeardownstreamfrom2010to2016)intheJDR(MessagerampOlden2018)andawin-dowofactivityof8ndash9months(basedonwatertemperaturesinthemainstem)rustycrayfishwouldhavetoachieveanetdownstreamspreadrateof80mdayonaveragewithoutconsideringtimeded-icatedtomatingandjuvenileparentalcareWespeculatethatthispacecouldrestricttheamountoftimeavailableforactivelypreyingoninvertebratesandcouldselectforthosecrayfishbestabletoef-ficientlyfeedandgrowonabundantandaccessiblebasalresourcesIthasalsobeenhypothesisedforstreamfishesthatthosenon-nativespeciesthatcansustaingrowthandreproductiononlow-qualityre-sourcesshouldbebestabletobecomeestablished(GidoampFranssen2007) Incrayfishabroader trophicniche thatexpandedtowardslower trophic levelsmayhaveaffordedcompetitiveadvantages totheintroducedsignalcrayfishoverthenativenoblecrayfishAstacus astacus inSwedishstreams (OlssonStenrothNystromampGraneli2009) Therefore our findings that rusty crayfish at the invasionfrontactmostlyasprimaryconsumerswhileachievinggreaterphys-iologicalconditionmightreflectanincreaseinfeedingefficiencyonbasal resources as a by-product of greater dispersal ability devel-opedthroughtheirrangeexpansionintheJDR
a crucial first step towards developing spatially explicit strategiestocontrol this invasion If thedocumentedphenotypicshifts fromcore to invasion front populations are indeed associatedwith theaccelerating rateof spreadof rusty crayfish then targeting thoseindividualsattheinvasionleadingedgeforremoval(egbytrapping)mightconstraintheaccumulationofdispersivephenotypesintheseareasAccountingforthesephenotypicshiftsinmechanisticmodelsofinvasivespread(egMessagerampOlden2018)couldalsoprovideuswithavirtual laboratorytotesttheeffectivenessofalternativecontrolstrategiesincontainingthespreadofriverineinvaderssuchasrustycrayfish
Our results suggest that low conspecific densities and spatialsortinginleading-edgepopulationsledtoashift inthephenotypeofrustycrayfishtowards lowercompetitiveabilityhigher intrinsicgrowthandorreproductionandgreaterforagingefficiencyonbasalresourcesastheyspreadupstreamanddownstreamintheJDROurstudydesignenabledustolinkmorphologicalandfunctionaltraitstobetterexploretheconsequencesofthisrangeexpansiononinvadedecosystemsWeexpectthatthediminishedcompetitiveabilityob-servedinthevanguardofthisrustycrayfishinvasionmightleadtoreducedfitnessoftheinvasionfrontphenotypesoncedensities innewlycolonisedareas limit theavailabilityofshelterand intensifycompetition formatesThe long-termevolutionary implicationsofthesephenotypicshiftsmightthusbelimited(PerkinsBoettigerampPhillips2016)Howeverthetrophicshiftobservedininvasionfrontpopulationscouldalsoallowrustycrayfishtoreachhigherdensitiesintheseareasastheymightexploitresourcesmorebroadlyandeffi-cientlyundercompetitiveconditionsTheevolutionaryforcesatplayinthisinvasionhaveprobablyinteractedwithlongitudinalgradientsinenvironmentalconditionsinwaysanalogoustothoseexperiencedbyspeciesduringtheirmigrationtowardscoolerareasunderclimatechangeIntegratingthestudyofmorphologicalandfunctionaltraitswith spatial variation in environmental conditions thus provides arobustwaytoassesswhethercontemporaryevolutionisalteringthephenotypeandecosystemimpactsofspeciesastheirrangeexpandsthroughthelandscape
Inconclusionthisstudyaddsevidenceinsupportofphenotypicchangesexpectedinnon-nativeorganismsexposedtochangingse-lectionpressuresas they invadenewenvironmentsDisentanglingthe causes of these changes whether related to environmentalfactorsorselectionduetorangeexpansionremainsan importantareaofinvestigationasweseektobetterunderstandtheecologicalimpactsofinvasivespeciesandhownativespecieswillrespondtoshiftingenvironmentalconditionsinthefuture
ACKNOWLEDG MENTS
WethankJeffAdamsEricLarsonDavidWoosterStephenBollensandKeithSorensonforprovidinghistoricaldataforrustycrayfishthe staff at theGrantCountyAssessorsoffice and the JohnDayFossilBedsNationalMonument for their help accessing the riverParticular appreciation goes to all the landowners throughout theJohnDayRiverbasin foraccess to their landandsupport for this
12emsp |emsp emspensp MESSAGER And OLdEn
projectWearegratefultoJacobCrunkforhisinestimablehelpwithfieldworkandEthenWhattamforhishelpprocessingmacroinver-tebratesamplesFromtheUniversityofWashingtonwethanktheMolecularEcologyResearchLaboratory(MERLab)andmorespecifi-callyIsadoraJimenez-HidalgoandNatalieLowelltheOldenlabaswellasJoshuaLawlerThomasQuinnandPatrickTobinThemanu-scriptwasimprovedbythecommentsfromtwoanonymousreview-ersFundingsupportwasprovidedbytheJohnNCobbScholarshipin Fisheries the Simpson Award from the Society for FreshwaterScienceandtheCrustaceanSocietyfellowshipinGraduateStudiesawarded to MLM and the University of Washington H MasonKeelerEndowedProfessorshipawardtoJDO
Mathis L Messager httpsorcidorg0000-0002-3051-8068
Julian D Olden httpsorcidorg0000-0003-2143-1187
R E FE R E N C E S
AndersonCampCabanaG (2007)Estimatingthetrophicpositionofaquatic consumers in river food webs using stable nitrogen iso-topes Journal of the North American Benthological Society 26(2)273ndash285 httpsdoiorg1018990887-3593(2007)26[273ettpoa]20co2
Arrington D A ampWinemiller K O (2002) Preservation effects onstable isotope analysis of fishmuscleTransactions of the American Fisheries Society131(2)337ndash342httpsdoiorg1015771548-8659(2002)131lt0337peosiagt20co2
Berdalet E Roldaacuten C ampOlivarM P (2005) Quantifying RNA andDNAinplanktonicorganismswithSYBRGreenIIandnucleasesPartBQuantification in natural samplesScientia Marina69(1) 17ndash30httpsdoiorg103989scimar200569n117
BerdaletERoldaacutenCOlivarMPampLysnesK (2005)QuantifyingRNAandDNAinplanktonicorganismswithSYBRGreenIIandnu-cleases Part A Optimisation of the assay Scientia Marina 69(1)1ndash16httpsdoiorg103989scimar200569n11
Bobeldyk A M amp Lamberti G A (2010) Stream food web re-sponses to a large omnivorous invader Orconectes rusticus (Decapoda Cambaridae) Crustaceana 83(6) 641ndash657 httpsdoiorg101163001121610x491031
BondarCABottriellKZeronKampRichardsonJS(2005)Doestro-phicpositionof theomnivoroussignalcrayfish (Pacifastacus lenius-culus) inastreamfoodwebvarywith lifehistorystageordensityCanadian Journal of Fisheries and Aquatic Sciences62(11)2632ndash2639httpsdoiorg101139f05-167
BrandnerJCerwenkaAFSchliewenUKampGeistJ(2013)BiggerisbetterCharacteristicsofroundgobiesforminganinvasionfrontinthe Danube River PLoS ONE8(9)e73036httpsdoiorg101371journalpone0073036
BrownGPKelehearCampShineR (2013)Theearly toadgets theworm Cane toads at an invasion front benefit from higher preyavailability Journal of Animal Ecology 82(4) 854ndash862 httpsdoiorg1011111365-265612048
Burton O J Phillips B L amp Travis J M J (2010) Trade-offs and the evolution of life-histories during range ex-pansion Ecology Letters 13(10) 1210ndash1220 httpsdoiorg101111j1461-0248201001505x
Capelli G M amp Hamilton P A (1984) Effects of food shelter andtimeof dayon aggressive activity in the crayfishOrconectes rusti-cus(Girard)Journal of Crustacean Biology4(2)252ndash260httpsdoiorg1011631937240x84x00363
Caplat P Cheptou P O Diez J Guisan A Larson B MMacDougall A S hellip Zhang R (2013) Movement impacts andmanagement of plant distributions in response to climate changeInsights from invasions Oikos 122(9) 1265ndash1274 httpsdoiorg101111j1600-0706201300430x
Chuang A amp Peterson C R (2016) Expanding population edgesTheories traits and trade-offsGlobal Change Biology22(2) 494ndash512httpsdoiorg101111gcb13107
ClarkJMKershnerMWampHolomuzkiJR(2008)Grainsizeandsorting effects on size-dependent responses by lotic crayfish tohigh flows Hydrobiologia 610 55ndash66 httpsdoiorg101007s10750-008-9422-0
CrandallKAampDeGraveS (2017)Anupdatedclassificationofthefreshwater crayfishes (Decapoda Astacidea) of the world with acompletespecieslistJournal of Crustacean Biology37(5)615ndash653httpsdoiorg101093jcbiolrux070
DavidsonAMJennionsMampNicotraAB(2011)Doinvasivespe-cies show higher phenotypic plasticity than native species and ifso is it adaptiveAmeta-analysisEcology Letters14(4) 419ndash431httpsdoiorg101111j1461-0248201101596x
DoddsWK Smith VH amp Lohman K (2002)Nitrogen and phos-phorusrelationshipstobenthicalgalbiomassintemperatestreamsCanadian Journal of Fisheries and Aquatic Sciences 59(5) 865ndash874httpsdoiorg101139f02-063
Fronhofer E A amp Altermatt F (2015) Eco-evolutionary feedbacksduring experimental range expansions Nature Communications 66844httpsdoiorg101038ncomms7844
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
8emsp |emsp emspensp MESSAGER And OLdEn
33emsp|emspTrophic position
Thetrophicpositionofrustycrayfishwasconsistentlylowerforin-dividualsat invasion fronts than inpopulationscloser to thecoredespite wide variations among sites throughout the catchment
(Figures3band4SupportingInformationAppendixS3)Inthemain-stemrustycrayfishdietfirstincreaseddownstreamfromthattypi-calofasecondaryconsumeroromnivore(trophicpositionofc 3) to thatofatopcarnivore(trophicpositionofc4)andthendecreasedtowardsthefrontoftheinvasiondowntothatofaprimaryconsumer
F IGURE 4emspSummary of the relationshipsbetweenrustycrayfishtraitsandpredictorvariablesintheJohnDayRiver The direction and colour of the arrowsindicatethesignoftherelationship(egredupwardarrowsreflectpositiverelationships)betweenthepredictorvariable(columns)andthetrait(rows)foragiveninvasionleadingedge(downstreammainstemupstreamSouthForkorupstreamNorthFork)Greyarrowsshowstatisticallynon-significantrelationshipsSignificanceandaconsistentdirectionintherelationshipbetweencandidatepredictorsandtraitsamongtributariessuggestedtheprimacyofthatpredictorindrivingobserveddifferencesintraitsSeeSupportingInformationAppendixS3fordetailedstatisticalresultsFlatgreenarrowsshowvariablesforwhichtherewasnodifferenceamongsitesinthattributaryandrelationshipsdenotedbyandashwerenottestedduetoalackofhypothesisedmechanismsrelatingthevariablesdaggerAsh-freedryweight
Response variable Edge
Predictor variableDistance
from introduction
Crayfish density
Degree days
Macroinv AFDWdagger
Green algae Diatom
Relative chela length
Mainstem
South Fork
North Fork
Trophic position
Mainstem
South Fork
North Fork
Physiological Condition
(RNADNA)
Mainstem
South Fork
North Fork
Carapace length
Mainstem
South Fork
North Fork
Relative weight
Mainstem
South Fork
North Fork
Sex ratio( males)
Mainstemndash ndash ndash ndash ndash
South Forkndash ndash ndash ndash ndash
North Forkndash ndash ndash ndash ndash
Carapace length SD
Mainstemndash ndash ndash ndash
South Forkndash ndash ndash ndash
North Forkndash ndash ndash ndash
daggerAsh-free dry weight
emspensp emsp | emsp9MESSAGER And OLdEn
(trophicpositionofc2GAMp=005R2-adjusted=044n = 14 Figure3b) Therewas an equivalent drop in crayfish trophic posi-tionintheNorthForkJDRupstreamleadingedge(t=966df=22plt0001)butnoequivalentdecreaseintheSouthForkJDRleadingedgeTherewasnodifferenceintrophicpositionamongmaleandfemalecrayfishandalthoughtrophicpositionwasweaklycorrelatedwithcarapacelengthwithinsites(carapacelengthfixedeffect95CI=80times10minus3to19times10minus2trophiclevelmminlinearmixedeffectmodelwithsiteasrandomeffect)therewasnosignificantcorrela-tionbetweentrophicpositionandmeancarapacelengthacrosssitesalongthemainstemTrophicpositionwasnotsignificantlycorrelatedwithrelativechelalengthwithinsites(relativechelalengthfixedef-fect 95 CI=minus83times10minus3 to 23times10minus2 trophic levelmm in linearmixedeffectmodelwithsiteasrandomeffect)
Temperature increasing with downstream distance from theinvasionsourcewascorrelatedwithtrophicpositiononlytowardstheupstreaminvasionfrontsintheNorthForkandSouthForkJDR(Figure4Supporting InformationAppendicesS2andS3)Noneoftheotherenvironmentalvariablessignificantlycovariedwithtrophicpositioninaconsistentwayacrosstributaries(Figure4SupportingInformationAppendicesS2andS3)
34emsp|emspGrowth and condition
There was a consistent positive trend in rusty crayfish physi-ological condition (RNADNA ratio) towards invasion fronts alongwith decreasing crayfish densities (Figures3c and 4 SupportingInformationAppendixS3)Strongesttowardstheupstreamleadingedgesdespitedecreasing temperature (t-test SouthForkW=46p-value=001North Fork t=minus491df=155plt0001) the in-creaseinphysiologicalconditionwasonlymarginalinthemainstem[GAMp=019R2-adjusted=006n=14meanslope=63times10minus3 (95CI=minus27times10minus3to15times10minus2) [RNADNA]km]Thenegativecorrelation between crayfish physiological condition (RNADNAratio)andcrayfishdensityinthemainstemwasalsonon-significant(GAM p=043 R2-adjusted=minus003 n=14) Lastly environmen-tal variables (abiotic and biotic)were not consistently and signifi-cantlyassociatedwithRNADNAratioacrosstributaries(Figure4SupportingInformationAppendixS3)
4emsp |emspDISCUSSION
Thisstudyrevealedsignificanttrendsinmorphologicaltraitvaluesphysiologicalconditionandtrophicpositionofrustycrayfishfromtheirlocationofinitialintroductiontomultipleleadingedgesofinva-sionintheonlyknownpopulationofthisspeciesinwesternNorthAmericaEventhoughthesetrendswerenotconsistentlysignificantacrosstributariestheysuggestthatrustycrayfishindividualsatthevanguard of the invasion exhibited less competitive morphology(decreasedrelativeweightandchelalength)andexploitedenergeticpathwaysloweronthefoodchainyetwereinbetterphysiologicalcondition than individuals located closer to the invasion coreWe
contendthatthesephenotypicshiftsobservedinrustycrayfishareprobablydue to the rangeexpansionprocess itself rather than tonovelenvironmentalconditionsattheirrangeboundariesandthatthesetrendsmayintensifyastheinvasioncontinuestounfoldup-stream and downstream towards the main stem of the ColumbiaRiver
The observed decrease in crayfish relative chela length andweighttowardstheinvasionfrontscanbeattributedtothreemainreasonsmdashalthough further research is needed to confirm the re-spectivecontributionifanyofeachofthesemechanismsFirsttherangeexpansionofrustycrayfishmightbedrivenbytheexclusionof subdominant individuals from high-density population centresthereforeleadingtothewidespreadpresenceofcompetitivelyinfe-riorcrayfishattheinvasionleadingedge(HudinaHockampZganec2014)Inotherwordsindividualcrayfishwithlesscompetitivephe-notypesmayhavebeenforcedoutandsystematically interbredatthe invasionfront resulting in theaccumulationof relatively lightsmall-clawedindividualsattheleadingedgeInsupportofthismech-anismsignalcrayfishattheboundaryoftheirinvasionrangeacrossCroatiadisplaylowerlevelsofaggressionandoftenloseagonisticin-teractionstoindividualsfromtheinvasioncoredespitebeinginbet-ter physical condition (Hudinaetal 2015)However a significantincreaseinrelativeclawsizeawayfromsourcepopulationwasalsoobservedininvasivesignalcrayfishmalesoftheMuraRiverCroatia(Hudinaetal2012)Secondlargerchelaeandastouterbodyshapemay be associated with weaker dispersal ability and thus be se-lectedagainstthroughassociativematingofthefastestdispersersclusteredattheinvasionleadingedgeCrayfishwithshorterchelaeandmorefusiformbodyarebetterabletowithstandhighwaterve-locitiesassuggestedbymorphologicdifferencesbetweencrayfishfound in high-velocity streams compared to those in low-velocitystreams and lakes (Perry etal 2013) Becausewater velocities inexcessof03ndash05msleadtodecreasedcrayfishmovementandpo-tentially increasedenergyexpenditureincrayfish(ClarkKershnerampHolomuzki 2008Matheramp Stein 1993 Perryamp Jones 2017)individualswithshorterchelaeandmorefusiformbodiesmaythusbeabletodisperseforlongerperiodsoftheyearintheJDRwhosedischarge isunregulatedbydamsandflowregimeischaracterisedbyspringsnowmeltThirdlowrustycrayfishconspecificdensitiesat invasion front sitesmay relax the constraints imposedby com-petitioninhigh-densityareasandthusreducetherequirementforinvestment in traitsassociatedwithcompetitionShelterandfoodlimitationsarethemaindriversofagonisticinteractionsincrayfish(BergmanampMoore2003CapelliampHamilton1984)Whentheseresourcesareplentiful inpioneerpopulationsbehaviouralpheno-typesassociatedwithlargeclawsandweightaspartofanaggressionsyndrome(Hudinaetal2012)couldthereforeleadtounnecessaryenergyexpensesand reduced foraging leading to reduced fitness(SihCoteEvansFogartyampPruitt2012)Thusashiftinselectivepressuremayhave led toachange in rustycrayfish lifehistoryattheedgeoftheinvasion involvingthereallocationofenergyfromallometricgrowthofcompetitivetraitstoreproductionanddisper-saltraitsnotmeasuredhere(egwalkingleglength)(Phillipsetal
Weconjecturethatashift intheselectionregimeexperiencedbyrustycrayfishfromcoretoleading-edgeareasisthemostprob-ableexplanationforthetrends inrelativechela lengthandweightobservedinthisstudyHoweverwithoutknowledgeoftheheritabil-ityofthecrayfishtraitsexaminedinthisstudyinferenceregardingthespecificmechanisms inoperation isstill limitedTheaccelerat-ingrateofspreadofrustycrayfish intheJDRthe lowpopulationdensities observedwithin several kilometres of the upstream anddownstreaminvasionfrontsandhighphysiologicalfitnessininva-sionfrontpopulationssuggestthatapushedinvasionexcludingsub-dominantcrayfishfromhigherdensityareasisunlikelytoexplaintheobservedtraitdifferencesMoreoverthereislittletonoevidenceoftheinfluenceofchelasizeorrelativebodyweightondispersalspeed(KamranampMoore 2015) Lastly the difference in relativeweightandchelalengthbetweeninvasioncoreandfrontpopulationscouldalsobedrivenbynaturalselectioninhighcrayfishdensitycorepop-ulationsHistoricaldatafromSorenson(2012)combinedwiththisstudy shownodifference inchela length (Supporting InformationFigureS51)butasignificantincreaseinrelativeweightfrom2010to2016atthepresumedsiteofrustycrayfishintroduction(SupportingInformationFigureS52)Thechangesintraitvaluesobservedherearethuslikelytobetheresultsofacombinationofdriversincludingreducedfitnessofcompetitivephenotypesatlowcrayfishdensityselectionforhighrelativeweightinthepopulationcoreandtrade-offsbetweenthesecompetitiveattributesandother traitsassoci-atedwithhigherdispersalability
Theobserved increase in rustycrayfishanabolicactivitymea-suredasRNADNAinleading-edgepopulationsoftheJDRalthoughweak in themainstem indicates that the rangeexpansionprocesshas led to greater somatic growth andor reproductive potentialin pioneer individuals This pattern matches several documentedincreases inbodyconditiongrowthandreproductivepotential insimilarstreaminvasionsbothwithinasingleinvasiongradientandbetweennativeandnon-nativepopulationsWithintheirnon-nativerange invasion front signal crayfish in Croatia and female spiny-cheekcrayfish in theDanubebothdisplayedgreater reproductivepotentials than their counterparts in core areas with the formeralsobeinginbetterconditionandenergeticstatus(Pacircrvulescuetal2015Rebrinaetal2015)Whencomparingnativeandnon-nativepopulationsofrustycrayfishbothlakeandmesocosmexperimentsfoundthatnon-nativeindividualshavehighergrowthratesandlevelsofactivitythantheirnativecongeners(PintorampSih2009Sargentamp Lodge 2014) Nonetheless whether the observed increase inrustycrayfishphysiologicalconditiontowardstheinvasionfront isassociated with greater somatic growth rates or gamete produc-tionremainsunresolvedandwarrantsfurtherinvestigationIndeed
simultaneous increases inconditiongrowthandreproductivepo-tentialarenotuniversalbecauseselectionfordispersalabilityduringrangeexpansionmay lead tounexpected trade-offsFor instancetadpolesandjuvenilesininvasionfrontpopulationsofcanetoadsintropicalAustraliagrowupto31fasterthanthosefromlongeres-tablishedpopulations(Phillips2009)andadultsdemonstratehigherfeeding rates larger fat stores andbetter condition thanconspe-cifics in later invasion stages (Brownetal2013)However lowerreproductiverateshavealsobeendocumentedincanetoadinvasionfrontpopulations(HudsonPhillipsBrownampShine2015)
Itmightseemthathighercrayfishgrowthratestowardstheinva-sionfrontscontradicttheobservedpatternsofreducedweightandchelalengthobservedinpioneercrayfishHoweverselectionforafasterlifestylecoulddecreaseageatmaturityandshortenthelifes-panoftheseinvasionfrontcrayfishwhileselectingagainstallome-tricgrowthofcompetitivemorphologyBothcrayfishgrowth rateandfecundityaredensitydependent(GuanampWiles1999MomotampGowing1977)Thereforeitispossiblethathighgrowthandfe-cundityphenotypeshavearisenfromnaturalselectioninthec 15 generationssincetheirintroductionaspartofadispersalsyndromeassociating rapid development and high fecunditywith dispersivetraits(RonceampClobert2012Stevensetal2013)
Rustycrayfishattheleadingedgesoftheirdistributionallimitsappeartobefeedinglowerinthefoodwebwhencomparedtocon-specifics locatedbehind the invasion frontThispattern stands incontradictionwithmostpreviousstudiesofstreaminvasionsRoundgobiesattheedgeoftheirexpandingrangeconsumemoreoftheirfavouredpreytypethanincentralpopulations(RabyGutowskyampFox2010)andhavehigherδ15Nsignaturesthanthepreviousyearfront(Brandneretal2013)Invasionfrontbloodyredmysidshrimp(Hemimysis anomala)werenotmoreselectiveintheirpreyconsump-tionbutshowedgreaterabilitytolocateandcapturezooplanktonprey than those shrimp in corepopulations (Iacarella etal 2015)ForcrayfishinvasionstrophicnicheshiftshaveonlybeenassessedatthebiogeographicalscaleandoffermixedinsightsInagreementwithourfindingsnon-nativepopulationsofrustycrayfishandvirilecrayfish(Faxonius virilis)appearedtoshowgreaterratesofalgaecon-sumption (despite constant macroinvertebrate prey consumption)thandidnativepopulationsinlaboratoryassays(Glonetal2018)By contrast an intercontinental stable isotope analysis revealedtrophicnicheconservatisminsignalcrayfishbetweenitsnativeandnon-native range (LarsonOldenampUsio 2010) Trophic flexibilityhasbeenshowntobespecies-dependenteveninsympatricnativecrayfishspecies (JohnstonRobsonampFairweather2011)andmaythus not be a consistent characteristic among invasive omnivoreseitherItisunlikelythatcannibalismawidespreadphenomenonincrayfishpopulations(GuanampWiles1998) ledtotheobservedin-creaseintrophicpositioninareaswithhighdensitiesofcrayfishasconspecificdensitywasnotcorrelatedtotrophicpositionintheJDR(Figure4SupportingInformationAppendixS3)Lastlyitisunlikelythatnon-crayfishpredatorsandcompetitorscouldhavedriventhisdownwardshiftinthetrophicpositionofrustycrayfishasthisshiftwasobservedacrossboththedownstream(increasingfishdensity)
Rustycrayfishhada lower trophicpositionevenwhenmacro-invertebrateprey availability increased towards the invasion frontintheNorthForkJDRThispatterncontrastedwithpastevidenceof a positive relationship between macroinvertebrate availabilityand crayfish trophic position (Olsson etal 2008) and greater as-similation efficiencies of invertebrates than other food items bycrayfish (WhitledgeampRabeni 1997)However the lackof signifi-cantdecreaseintrophicpositiontowardstheinvasionfront intheSouth Fork JDR could be due to a counter-effect from increasingmacroinvertebrate biomass upstream Consumption of macroin-vertebrateshasbeen linkedto increases inweightgainandmeta-bolicrates(BondarBottriellZeronampRichardson2005Hilletal1993 McFeeters Xenopoulos Spooner Wagner amp Frost 2011)Nevertheless in these same studies juvenile signal crayfish in anatural settingdisproportionatelyconsumedfoodtypes thatweretheoppositeofthoseshowntobeofmostnutritionalvaluetothem(Bondar etal 2005) and rusty crayfishmortalitywashigheron adietbasedoninvertebratethanoneonperiphytonordetritus(Hilletal 1993) This suggests that high growth might be associatedwith greater physiological stress due tomore frequentmoultingandhigherforagingcostsinnaturalsettingsThuswehypothesisethatenergyintakeandlong-termfitnessofrustycrayfishassociatedwithperiphytonanddetritusconsumptionmaybehigherthanwithmacroinvertebratedietsdespitetheir lowerdigestionefficiencyoftheseresources
Trade-offs can also arise between increased dispersal rates atrangemarginsand the functional responseof thenon-nativecon-sumer due to the high cost of dispersal (Fronhofer amp Altermatt2015)Giventheircurrentrateofspread(c20kmyeardownstreamfrom2010to2016)intheJDR(MessagerampOlden2018)andawin-dowofactivityof8ndash9months(basedonwatertemperaturesinthemainstem)rustycrayfishwouldhavetoachieveanetdownstreamspreadrateof80mdayonaveragewithoutconsideringtimeded-icatedtomatingandjuvenileparentalcareWespeculatethatthispacecouldrestricttheamountoftimeavailableforactivelypreyingoninvertebratesandcouldselectforthosecrayfishbestabletoef-ficientlyfeedandgrowonabundantandaccessiblebasalresourcesIthasalsobeenhypothesisedforstreamfishesthatthosenon-nativespeciesthatcansustaingrowthandreproductiononlow-qualityre-sourcesshouldbebestabletobecomeestablished(GidoampFranssen2007) Incrayfishabroader trophicniche thatexpandedtowardslower trophic levelsmayhaveaffordedcompetitiveadvantages totheintroducedsignalcrayfishoverthenativenoblecrayfishAstacus astacus inSwedishstreams (OlssonStenrothNystromampGraneli2009) Therefore our findings that rusty crayfish at the invasionfrontactmostlyasprimaryconsumerswhileachievinggreaterphys-iologicalconditionmightreflectanincreaseinfeedingefficiencyonbasal resources as a by-product of greater dispersal ability devel-opedthroughtheirrangeexpansionintheJDR
a crucial first step towards developing spatially explicit strategiestocontrol this invasion If thedocumentedphenotypicshifts fromcore to invasion front populations are indeed associatedwith theaccelerating rateof spreadof rusty crayfish then targeting thoseindividualsattheinvasionleadingedgeforremoval(egbytrapping)mightconstraintheaccumulationofdispersivephenotypesintheseareasAccountingforthesephenotypicshiftsinmechanisticmodelsofinvasivespread(egMessagerampOlden2018)couldalsoprovideuswithavirtual laboratorytotesttheeffectivenessofalternativecontrolstrategiesincontainingthespreadofriverineinvaderssuchasrustycrayfish
Our results suggest that low conspecific densities and spatialsortinginleading-edgepopulationsledtoashift inthephenotypeofrustycrayfishtowards lowercompetitiveabilityhigher intrinsicgrowthandorreproductionandgreaterforagingefficiencyonbasalresourcesastheyspreadupstreamanddownstreamintheJDROurstudydesignenabledustolinkmorphologicalandfunctionaltraitstobetterexploretheconsequencesofthisrangeexpansiononinvadedecosystemsWeexpectthatthediminishedcompetitiveabilityob-servedinthevanguardofthisrustycrayfishinvasionmightleadtoreducedfitnessoftheinvasionfrontphenotypesoncedensities innewlycolonisedareas limit theavailabilityofshelterand intensifycompetition formatesThe long-termevolutionary implicationsofthesephenotypicshiftsmightthusbelimited(PerkinsBoettigerampPhillips2016)Howeverthetrophicshiftobservedininvasionfrontpopulationscouldalsoallowrustycrayfishtoreachhigherdensitiesintheseareasastheymightexploitresourcesmorebroadlyandeffi-cientlyundercompetitiveconditionsTheevolutionaryforcesatplayinthisinvasionhaveprobablyinteractedwithlongitudinalgradientsinenvironmentalconditionsinwaysanalogoustothoseexperiencedbyspeciesduringtheirmigrationtowardscoolerareasunderclimatechangeIntegratingthestudyofmorphologicalandfunctionaltraitswith spatial variation in environmental conditions thus provides arobustwaytoassesswhethercontemporaryevolutionisalteringthephenotypeandecosystemimpactsofspeciesastheirrangeexpandsthroughthelandscape
Inconclusionthisstudyaddsevidenceinsupportofphenotypicchangesexpectedinnon-nativeorganismsexposedtochangingse-lectionpressuresas they invadenewenvironmentsDisentanglingthe causes of these changes whether related to environmentalfactorsorselectionduetorangeexpansionremainsan importantareaofinvestigationasweseektobetterunderstandtheecologicalimpactsofinvasivespeciesandhownativespecieswillrespondtoshiftingenvironmentalconditionsinthefuture
ACKNOWLEDG MENTS
WethankJeffAdamsEricLarsonDavidWoosterStephenBollensandKeithSorensonforprovidinghistoricaldataforrustycrayfishthe staff at theGrantCountyAssessorsoffice and the JohnDayFossilBedsNationalMonument for their help accessing the riverParticular appreciation goes to all the landowners throughout theJohnDayRiverbasin foraccess to their landandsupport for this
12emsp |emsp emspensp MESSAGER And OLdEn
projectWearegratefultoJacobCrunkforhisinestimablehelpwithfieldworkandEthenWhattamforhishelpprocessingmacroinver-tebratesamplesFromtheUniversityofWashingtonwethanktheMolecularEcologyResearchLaboratory(MERLab)andmorespecifi-callyIsadoraJimenez-HidalgoandNatalieLowelltheOldenlabaswellasJoshuaLawlerThomasQuinnandPatrickTobinThemanu-scriptwasimprovedbythecommentsfromtwoanonymousreview-ersFundingsupportwasprovidedbytheJohnNCobbScholarshipin Fisheries the Simpson Award from the Society for FreshwaterScienceandtheCrustaceanSocietyfellowshipinGraduateStudiesawarded to MLM and the University of Washington H MasonKeelerEndowedProfessorshipawardtoJDO
Mathis L Messager httpsorcidorg0000-0002-3051-8068
Julian D Olden httpsorcidorg0000-0003-2143-1187
R E FE R E N C E S
AndersonCampCabanaG (2007)Estimatingthetrophicpositionofaquatic consumers in river food webs using stable nitrogen iso-topes Journal of the North American Benthological Society 26(2)273ndash285 httpsdoiorg1018990887-3593(2007)26[273ettpoa]20co2
Arrington D A ampWinemiller K O (2002) Preservation effects onstable isotope analysis of fishmuscleTransactions of the American Fisheries Society131(2)337ndash342httpsdoiorg1015771548-8659(2002)131lt0337peosiagt20co2
Berdalet E Roldaacuten C ampOlivarM P (2005) Quantifying RNA andDNAinplanktonicorganismswithSYBRGreenIIandnucleasesPartBQuantification in natural samplesScientia Marina69(1) 17ndash30httpsdoiorg103989scimar200569n117
BerdaletERoldaacutenCOlivarMPampLysnesK (2005)QuantifyingRNAandDNAinplanktonicorganismswithSYBRGreenIIandnu-cleases Part A Optimisation of the assay Scientia Marina 69(1)1ndash16httpsdoiorg103989scimar200569n11
Bobeldyk A M amp Lamberti G A (2010) Stream food web re-sponses to a large omnivorous invader Orconectes rusticus (Decapoda Cambaridae) Crustaceana 83(6) 641ndash657 httpsdoiorg101163001121610x491031
BondarCABottriellKZeronKampRichardsonJS(2005)Doestro-phicpositionof theomnivoroussignalcrayfish (Pacifastacus lenius-culus) inastreamfoodwebvarywith lifehistorystageordensityCanadian Journal of Fisheries and Aquatic Sciences62(11)2632ndash2639httpsdoiorg101139f05-167
BrandnerJCerwenkaAFSchliewenUKampGeistJ(2013)BiggerisbetterCharacteristicsofroundgobiesforminganinvasionfrontinthe Danube River PLoS ONE8(9)e73036httpsdoiorg101371journalpone0073036
BrownGPKelehearCampShineR (2013)Theearly toadgets theworm Cane toads at an invasion front benefit from higher preyavailability Journal of Animal Ecology 82(4) 854ndash862 httpsdoiorg1011111365-265612048
Burton O J Phillips B L amp Travis J M J (2010) Trade-offs and the evolution of life-histories during range ex-pansion Ecology Letters 13(10) 1210ndash1220 httpsdoiorg101111j1461-0248201001505x
Capelli G M amp Hamilton P A (1984) Effects of food shelter andtimeof dayon aggressive activity in the crayfishOrconectes rusti-cus(Girard)Journal of Crustacean Biology4(2)252ndash260httpsdoiorg1011631937240x84x00363
Caplat P Cheptou P O Diez J Guisan A Larson B MMacDougall A S hellip Zhang R (2013) Movement impacts andmanagement of plant distributions in response to climate changeInsights from invasions Oikos 122(9) 1265ndash1274 httpsdoiorg101111j1600-0706201300430x
Chuang A amp Peterson C R (2016) Expanding population edgesTheories traits and trade-offsGlobal Change Biology22(2) 494ndash512httpsdoiorg101111gcb13107
ClarkJMKershnerMWampHolomuzkiJR(2008)Grainsizeandsorting effects on size-dependent responses by lotic crayfish tohigh flows Hydrobiologia 610 55ndash66 httpsdoiorg101007s10750-008-9422-0
CrandallKAampDeGraveS (2017)Anupdatedclassificationofthefreshwater crayfishes (Decapoda Astacidea) of the world with acompletespecieslistJournal of Crustacean Biology37(5)615ndash653httpsdoiorg101093jcbiolrux070
DavidsonAMJennionsMampNicotraAB(2011)Doinvasivespe-cies show higher phenotypic plasticity than native species and ifso is it adaptiveAmeta-analysisEcology Letters14(4) 419ndash431httpsdoiorg101111j1461-0248201101596x
DoddsWK Smith VH amp Lohman K (2002)Nitrogen and phos-phorusrelationshipstobenthicalgalbiomassintemperatestreamsCanadian Journal of Fisheries and Aquatic Sciences 59(5) 865ndash874httpsdoiorg101139f02-063
Fronhofer E A amp Altermatt F (2015) Eco-evolutionary feedbacksduring experimental range expansions Nature Communications 66844httpsdoiorg101038ncomms7844
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
emspensp emsp | emsp9MESSAGER And OLdEn
(trophicpositionofc2GAMp=005R2-adjusted=044n = 14 Figure3b) Therewas an equivalent drop in crayfish trophic posi-tionintheNorthForkJDRupstreamleadingedge(t=966df=22plt0001)butnoequivalentdecreaseintheSouthForkJDRleadingedgeTherewasnodifferenceintrophicpositionamongmaleandfemalecrayfishandalthoughtrophicpositionwasweaklycorrelatedwithcarapacelengthwithinsites(carapacelengthfixedeffect95CI=80times10minus3to19times10minus2trophiclevelmminlinearmixedeffectmodelwithsiteasrandomeffect)therewasnosignificantcorrela-tionbetweentrophicpositionandmeancarapacelengthacrosssitesalongthemainstemTrophicpositionwasnotsignificantlycorrelatedwithrelativechelalengthwithinsites(relativechelalengthfixedef-fect 95 CI=minus83times10minus3 to 23times10minus2 trophic levelmm in linearmixedeffectmodelwithsiteasrandomeffect)
Temperature increasing with downstream distance from theinvasionsourcewascorrelatedwithtrophicpositiononlytowardstheupstreaminvasionfrontsintheNorthForkandSouthForkJDR(Figure4Supporting InformationAppendicesS2andS3)Noneoftheotherenvironmentalvariablessignificantlycovariedwithtrophicpositioninaconsistentwayacrosstributaries(Figure4SupportingInformationAppendicesS2andS3)
34emsp|emspGrowth and condition
There was a consistent positive trend in rusty crayfish physi-ological condition (RNADNA ratio) towards invasion fronts alongwith decreasing crayfish densities (Figures3c and 4 SupportingInformationAppendixS3)Strongesttowardstheupstreamleadingedgesdespitedecreasing temperature (t-test SouthForkW=46p-value=001North Fork t=minus491df=155plt0001) the in-creaseinphysiologicalconditionwasonlymarginalinthemainstem[GAMp=019R2-adjusted=006n=14meanslope=63times10minus3 (95CI=minus27times10minus3to15times10minus2) [RNADNA]km]Thenegativecorrelation between crayfish physiological condition (RNADNAratio)andcrayfishdensityinthemainstemwasalsonon-significant(GAM p=043 R2-adjusted=minus003 n=14) Lastly environmen-tal variables (abiotic and biotic)were not consistently and signifi-cantlyassociatedwithRNADNAratioacrosstributaries(Figure4SupportingInformationAppendixS3)
4emsp |emspDISCUSSION
Thisstudyrevealedsignificanttrendsinmorphologicaltraitvaluesphysiologicalconditionandtrophicpositionofrustycrayfishfromtheirlocationofinitialintroductiontomultipleleadingedgesofinva-sionintheonlyknownpopulationofthisspeciesinwesternNorthAmericaEventhoughthesetrendswerenotconsistentlysignificantacrosstributariestheysuggestthatrustycrayfishindividualsatthevanguard of the invasion exhibited less competitive morphology(decreasedrelativeweightandchelalength)andexploitedenergeticpathwaysloweronthefoodchainyetwereinbetterphysiologicalcondition than individuals located closer to the invasion coreWe
contendthatthesephenotypicshiftsobservedinrustycrayfishareprobablydue to the rangeexpansionprocess itself rather than tonovelenvironmentalconditionsattheirrangeboundariesandthatthesetrendsmayintensifyastheinvasioncontinuestounfoldup-stream and downstream towards the main stem of the ColumbiaRiver
The observed decrease in crayfish relative chela length andweighttowardstheinvasionfrontscanbeattributedtothreemainreasonsmdashalthough further research is needed to confirm the re-spectivecontributionifanyofeachofthesemechanismsFirsttherangeexpansionofrustycrayfishmightbedrivenbytheexclusionof subdominant individuals from high-density population centresthereforeleadingtothewidespreadpresenceofcompetitivelyinfe-riorcrayfishattheinvasionleadingedge(HudinaHockampZganec2014)Inotherwordsindividualcrayfishwithlesscompetitivephe-notypesmayhavebeenforcedoutandsystematically interbredatthe invasionfront resulting in theaccumulationof relatively lightsmall-clawedindividualsattheleadingedgeInsupportofthismech-anismsignalcrayfishattheboundaryoftheirinvasionrangeacrossCroatiadisplaylowerlevelsofaggressionandoftenloseagonisticin-teractionstoindividualsfromtheinvasioncoredespitebeinginbet-ter physical condition (Hudinaetal 2015)However a significantincreaseinrelativeclawsizeawayfromsourcepopulationwasalsoobservedininvasivesignalcrayfishmalesoftheMuraRiverCroatia(Hudinaetal2012)Secondlargerchelaeandastouterbodyshapemay be associated with weaker dispersal ability and thus be se-lectedagainstthroughassociativematingofthefastestdispersersclusteredattheinvasionleadingedgeCrayfishwithshorterchelaeandmorefusiformbodyarebetterabletowithstandhighwaterve-locitiesassuggestedbymorphologicdifferencesbetweencrayfishfound in high-velocity streams compared to those in low-velocitystreams and lakes (Perry etal 2013) Becausewater velocities inexcessof03ndash05msleadtodecreasedcrayfishmovementandpo-tentially increasedenergyexpenditureincrayfish(ClarkKershnerampHolomuzki 2008Matheramp Stein 1993 Perryamp Jones 2017)individualswithshorterchelaeandmorefusiformbodiesmaythusbeabletodisperseforlongerperiodsoftheyearintheJDRwhosedischarge isunregulatedbydamsandflowregimeischaracterisedbyspringsnowmeltThirdlowrustycrayfishconspecificdensitiesat invasion front sitesmay relax the constraints imposedby com-petitioninhigh-densityareasandthusreducetherequirementforinvestment in traitsassociatedwithcompetitionShelterandfoodlimitationsarethemaindriversofagonisticinteractionsincrayfish(BergmanampMoore2003CapelliampHamilton1984)Whentheseresourcesareplentiful inpioneerpopulationsbehaviouralpheno-typesassociatedwithlargeclawsandweightaspartofanaggressionsyndrome(Hudinaetal2012)couldthereforeleadtounnecessaryenergyexpensesand reduced foraging leading to reduced fitness(SihCoteEvansFogartyampPruitt2012)Thusashiftinselectivepressuremayhave led toachange in rustycrayfish lifehistoryattheedgeoftheinvasion involvingthereallocationofenergyfromallometricgrowthofcompetitivetraitstoreproductionanddisper-saltraitsnotmeasuredhere(egwalkingleglength)(Phillipsetal
Weconjecturethatashift intheselectionregimeexperiencedbyrustycrayfishfromcoretoleading-edgeareasisthemostprob-ableexplanationforthetrends inrelativechela lengthandweightobservedinthisstudyHoweverwithoutknowledgeoftheheritabil-ityofthecrayfishtraitsexaminedinthisstudyinferenceregardingthespecificmechanisms inoperation isstill limitedTheaccelerat-ingrateofspreadofrustycrayfish intheJDRthe lowpopulationdensities observedwithin several kilometres of the upstream anddownstreaminvasionfrontsandhighphysiologicalfitnessininva-sionfrontpopulationssuggestthatapushedinvasionexcludingsub-dominantcrayfishfromhigherdensityareasisunlikelytoexplaintheobservedtraitdifferencesMoreoverthereislittletonoevidenceoftheinfluenceofchelasizeorrelativebodyweightondispersalspeed(KamranampMoore 2015) Lastly the difference in relativeweightandchelalengthbetweeninvasioncoreandfrontpopulationscouldalsobedrivenbynaturalselectioninhighcrayfishdensitycorepop-ulationsHistoricaldatafromSorenson(2012)combinedwiththisstudy shownodifference inchela length (Supporting InformationFigureS51)butasignificantincreaseinrelativeweightfrom2010to2016atthepresumedsiteofrustycrayfishintroduction(SupportingInformationFigureS52)Thechangesintraitvaluesobservedherearethuslikelytobetheresultsofacombinationofdriversincludingreducedfitnessofcompetitivephenotypesatlowcrayfishdensityselectionforhighrelativeweightinthepopulationcoreandtrade-offsbetweenthesecompetitiveattributesandother traitsassoci-atedwithhigherdispersalability
Theobserved increase in rustycrayfishanabolicactivitymea-suredasRNADNAinleading-edgepopulationsoftheJDRalthoughweak in themainstem indicates that the rangeexpansionprocesshas led to greater somatic growth andor reproductive potentialin pioneer individuals This pattern matches several documentedincreases inbodyconditiongrowthandreproductivepotential insimilarstreaminvasionsbothwithinasingleinvasiongradientandbetweennativeandnon-nativepopulationsWithintheirnon-nativerange invasion front signal crayfish in Croatia and female spiny-cheekcrayfish in theDanubebothdisplayedgreater reproductivepotentials than their counterparts in core areas with the formeralsobeinginbetterconditionandenergeticstatus(Pacircrvulescuetal2015Rebrinaetal2015)Whencomparingnativeandnon-nativepopulationsofrustycrayfishbothlakeandmesocosmexperimentsfoundthatnon-nativeindividualshavehighergrowthratesandlevelsofactivitythantheirnativecongeners(PintorampSih2009Sargentamp Lodge 2014) Nonetheless whether the observed increase inrustycrayfishphysiologicalconditiontowardstheinvasionfront isassociated with greater somatic growth rates or gamete produc-tionremainsunresolvedandwarrantsfurtherinvestigationIndeed
simultaneous increases inconditiongrowthandreproductivepo-tentialarenotuniversalbecauseselectionfordispersalabilityduringrangeexpansionmay lead tounexpected trade-offsFor instancetadpolesandjuvenilesininvasionfrontpopulationsofcanetoadsintropicalAustraliagrowupto31fasterthanthosefromlongeres-tablishedpopulations(Phillips2009)andadultsdemonstratehigherfeeding rates larger fat stores andbetter condition thanconspe-cifics in later invasion stages (Brownetal2013)However lowerreproductiverateshavealsobeendocumentedincanetoadinvasionfrontpopulations(HudsonPhillipsBrownampShine2015)
Itmightseemthathighercrayfishgrowthratestowardstheinva-sionfrontscontradicttheobservedpatternsofreducedweightandchelalengthobservedinpioneercrayfishHoweverselectionforafasterlifestylecoulddecreaseageatmaturityandshortenthelifes-panoftheseinvasionfrontcrayfishwhileselectingagainstallome-tricgrowthofcompetitivemorphologyBothcrayfishgrowth rateandfecundityaredensitydependent(GuanampWiles1999MomotampGowing1977)Thereforeitispossiblethathighgrowthandfe-cundityphenotypeshavearisenfromnaturalselectioninthec 15 generationssincetheirintroductionaspartofadispersalsyndromeassociating rapid development and high fecunditywith dispersivetraits(RonceampClobert2012Stevensetal2013)
Rustycrayfishattheleadingedgesoftheirdistributionallimitsappeartobefeedinglowerinthefoodwebwhencomparedtocon-specifics locatedbehind the invasion frontThispattern stands incontradictionwithmostpreviousstudiesofstreaminvasionsRoundgobiesattheedgeoftheirexpandingrangeconsumemoreoftheirfavouredpreytypethanincentralpopulations(RabyGutowskyampFox2010)andhavehigherδ15Nsignaturesthanthepreviousyearfront(Brandneretal2013)Invasionfrontbloodyredmysidshrimp(Hemimysis anomala)werenotmoreselectiveintheirpreyconsump-tionbutshowedgreaterabilitytolocateandcapturezooplanktonprey than those shrimp in corepopulations (Iacarella etal 2015)ForcrayfishinvasionstrophicnicheshiftshaveonlybeenassessedatthebiogeographicalscaleandoffermixedinsightsInagreementwithourfindingsnon-nativepopulationsofrustycrayfishandvirilecrayfish(Faxonius virilis)appearedtoshowgreaterratesofalgaecon-sumption (despite constant macroinvertebrate prey consumption)thandidnativepopulationsinlaboratoryassays(Glonetal2018)By contrast an intercontinental stable isotope analysis revealedtrophicnicheconservatisminsignalcrayfishbetweenitsnativeandnon-native range (LarsonOldenampUsio 2010) Trophic flexibilityhasbeenshowntobespecies-dependenteveninsympatricnativecrayfishspecies (JohnstonRobsonampFairweather2011)andmaythus not be a consistent characteristic among invasive omnivoreseitherItisunlikelythatcannibalismawidespreadphenomenonincrayfishpopulations(GuanampWiles1998) ledtotheobservedin-creaseintrophicpositioninareaswithhighdensitiesofcrayfishasconspecificdensitywasnotcorrelatedtotrophicpositionintheJDR(Figure4SupportingInformationAppendixS3)Lastlyitisunlikelythatnon-crayfishpredatorsandcompetitorscouldhavedriventhisdownwardshiftinthetrophicpositionofrustycrayfishasthisshiftwasobservedacrossboththedownstream(increasingfishdensity)
Rustycrayfishhada lower trophicpositionevenwhenmacro-invertebrateprey availability increased towards the invasion frontintheNorthForkJDRThispatterncontrastedwithpastevidenceof a positive relationship between macroinvertebrate availabilityand crayfish trophic position (Olsson etal 2008) and greater as-similation efficiencies of invertebrates than other food items bycrayfish (WhitledgeampRabeni 1997)However the lackof signifi-cantdecreaseintrophicpositiontowardstheinvasionfront intheSouth Fork JDR could be due to a counter-effect from increasingmacroinvertebrate biomass upstream Consumption of macroin-vertebrateshasbeen linkedto increases inweightgainandmeta-bolicrates(BondarBottriellZeronampRichardson2005Hilletal1993 McFeeters Xenopoulos Spooner Wagner amp Frost 2011)Nevertheless in these same studies juvenile signal crayfish in anatural settingdisproportionatelyconsumedfoodtypes thatweretheoppositeofthoseshowntobeofmostnutritionalvaluetothem(Bondar etal 2005) and rusty crayfishmortalitywashigheron adietbasedoninvertebratethanoneonperiphytonordetritus(Hilletal 1993) This suggests that high growth might be associatedwith greater physiological stress due tomore frequentmoultingandhigherforagingcostsinnaturalsettingsThuswehypothesisethatenergyintakeandlong-termfitnessofrustycrayfishassociatedwithperiphytonanddetritusconsumptionmaybehigherthanwithmacroinvertebratedietsdespitetheir lowerdigestionefficiencyoftheseresources
Trade-offs can also arise between increased dispersal rates atrangemarginsand the functional responseof thenon-nativecon-sumer due to the high cost of dispersal (Fronhofer amp Altermatt2015)Giventheircurrentrateofspread(c20kmyeardownstreamfrom2010to2016)intheJDR(MessagerampOlden2018)andawin-dowofactivityof8ndash9months(basedonwatertemperaturesinthemainstem)rustycrayfishwouldhavetoachieveanetdownstreamspreadrateof80mdayonaveragewithoutconsideringtimeded-icatedtomatingandjuvenileparentalcareWespeculatethatthispacecouldrestricttheamountoftimeavailableforactivelypreyingoninvertebratesandcouldselectforthosecrayfishbestabletoef-ficientlyfeedandgrowonabundantandaccessiblebasalresourcesIthasalsobeenhypothesisedforstreamfishesthatthosenon-nativespeciesthatcansustaingrowthandreproductiononlow-qualityre-sourcesshouldbebestabletobecomeestablished(GidoampFranssen2007) Incrayfishabroader trophicniche thatexpandedtowardslower trophic levelsmayhaveaffordedcompetitiveadvantages totheintroducedsignalcrayfishoverthenativenoblecrayfishAstacus astacus inSwedishstreams (OlssonStenrothNystromampGraneli2009) Therefore our findings that rusty crayfish at the invasionfrontactmostlyasprimaryconsumerswhileachievinggreaterphys-iologicalconditionmightreflectanincreaseinfeedingefficiencyonbasal resources as a by-product of greater dispersal ability devel-opedthroughtheirrangeexpansionintheJDR
a crucial first step towards developing spatially explicit strategiestocontrol this invasion If thedocumentedphenotypicshifts fromcore to invasion front populations are indeed associatedwith theaccelerating rateof spreadof rusty crayfish then targeting thoseindividualsattheinvasionleadingedgeforremoval(egbytrapping)mightconstraintheaccumulationofdispersivephenotypesintheseareasAccountingforthesephenotypicshiftsinmechanisticmodelsofinvasivespread(egMessagerampOlden2018)couldalsoprovideuswithavirtual laboratorytotesttheeffectivenessofalternativecontrolstrategiesincontainingthespreadofriverineinvaderssuchasrustycrayfish
Our results suggest that low conspecific densities and spatialsortinginleading-edgepopulationsledtoashift inthephenotypeofrustycrayfishtowards lowercompetitiveabilityhigher intrinsicgrowthandorreproductionandgreaterforagingefficiencyonbasalresourcesastheyspreadupstreamanddownstreamintheJDROurstudydesignenabledustolinkmorphologicalandfunctionaltraitstobetterexploretheconsequencesofthisrangeexpansiononinvadedecosystemsWeexpectthatthediminishedcompetitiveabilityob-servedinthevanguardofthisrustycrayfishinvasionmightleadtoreducedfitnessoftheinvasionfrontphenotypesoncedensities innewlycolonisedareas limit theavailabilityofshelterand intensifycompetition formatesThe long-termevolutionary implicationsofthesephenotypicshiftsmightthusbelimited(PerkinsBoettigerampPhillips2016)Howeverthetrophicshiftobservedininvasionfrontpopulationscouldalsoallowrustycrayfishtoreachhigherdensitiesintheseareasastheymightexploitresourcesmorebroadlyandeffi-cientlyundercompetitiveconditionsTheevolutionaryforcesatplayinthisinvasionhaveprobablyinteractedwithlongitudinalgradientsinenvironmentalconditionsinwaysanalogoustothoseexperiencedbyspeciesduringtheirmigrationtowardscoolerareasunderclimatechangeIntegratingthestudyofmorphologicalandfunctionaltraitswith spatial variation in environmental conditions thus provides arobustwaytoassesswhethercontemporaryevolutionisalteringthephenotypeandecosystemimpactsofspeciesastheirrangeexpandsthroughthelandscape
Inconclusionthisstudyaddsevidenceinsupportofphenotypicchangesexpectedinnon-nativeorganismsexposedtochangingse-lectionpressuresas they invadenewenvironmentsDisentanglingthe causes of these changes whether related to environmentalfactorsorselectionduetorangeexpansionremainsan importantareaofinvestigationasweseektobetterunderstandtheecologicalimpactsofinvasivespeciesandhownativespecieswillrespondtoshiftingenvironmentalconditionsinthefuture
ACKNOWLEDG MENTS
WethankJeffAdamsEricLarsonDavidWoosterStephenBollensandKeithSorensonforprovidinghistoricaldataforrustycrayfishthe staff at theGrantCountyAssessorsoffice and the JohnDayFossilBedsNationalMonument for their help accessing the riverParticular appreciation goes to all the landowners throughout theJohnDayRiverbasin foraccess to their landandsupport for this
12emsp |emsp emspensp MESSAGER And OLdEn
projectWearegratefultoJacobCrunkforhisinestimablehelpwithfieldworkandEthenWhattamforhishelpprocessingmacroinver-tebratesamplesFromtheUniversityofWashingtonwethanktheMolecularEcologyResearchLaboratory(MERLab)andmorespecifi-callyIsadoraJimenez-HidalgoandNatalieLowelltheOldenlabaswellasJoshuaLawlerThomasQuinnandPatrickTobinThemanu-scriptwasimprovedbythecommentsfromtwoanonymousreview-ersFundingsupportwasprovidedbytheJohnNCobbScholarshipin Fisheries the Simpson Award from the Society for FreshwaterScienceandtheCrustaceanSocietyfellowshipinGraduateStudiesawarded to MLM and the University of Washington H MasonKeelerEndowedProfessorshipawardtoJDO
Mathis L Messager httpsorcidorg0000-0002-3051-8068
Julian D Olden httpsorcidorg0000-0003-2143-1187
R E FE R E N C E S
AndersonCampCabanaG (2007)Estimatingthetrophicpositionofaquatic consumers in river food webs using stable nitrogen iso-topes Journal of the North American Benthological Society 26(2)273ndash285 httpsdoiorg1018990887-3593(2007)26[273ettpoa]20co2
Arrington D A ampWinemiller K O (2002) Preservation effects onstable isotope analysis of fishmuscleTransactions of the American Fisheries Society131(2)337ndash342httpsdoiorg1015771548-8659(2002)131lt0337peosiagt20co2
Berdalet E Roldaacuten C ampOlivarM P (2005) Quantifying RNA andDNAinplanktonicorganismswithSYBRGreenIIandnucleasesPartBQuantification in natural samplesScientia Marina69(1) 17ndash30httpsdoiorg103989scimar200569n117
BerdaletERoldaacutenCOlivarMPampLysnesK (2005)QuantifyingRNAandDNAinplanktonicorganismswithSYBRGreenIIandnu-cleases Part A Optimisation of the assay Scientia Marina 69(1)1ndash16httpsdoiorg103989scimar200569n11
Bobeldyk A M amp Lamberti G A (2010) Stream food web re-sponses to a large omnivorous invader Orconectes rusticus (Decapoda Cambaridae) Crustaceana 83(6) 641ndash657 httpsdoiorg101163001121610x491031
BondarCABottriellKZeronKampRichardsonJS(2005)Doestro-phicpositionof theomnivoroussignalcrayfish (Pacifastacus lenius-culus) inastreamfoodwebvarywith lifehistorystageordensityCanadian Journal of Fisheries and Aquatic Sciences62(11)2632ndash2639httpsdoiorg101139f05-167
BrandnerJCerwenkaAFSchliewenUKampGeistJ(2013)BiggerisbetterCharacteristicsofroundgobiesforminganinvasionfrontinthe Danube River PLoS ONE8(9)e73036httpsdoiorg101371journalpone0073036
BrownGPKelehearCampShineR (2013)Theearly toadgets theworm Cane toads at an invasion front benefit from higher preyavailability Journal of Animal Ecology 82(4) 854ndash862 httpsdoiorg1011111365-265612048
Burton O J Phillips B L amp Travis J M J (2010) Trade-offs and the evolution of life-histories during range ex-pansion Ecology Letters 13(10) 1210ndash1220 httpsdoiorg101111j1461-0248201001505x
Capelli G M amp Hamilton P A (1984) Effects of food shelter andtimeof dayon aggressive activity in the crayfishOrconectes rusti-cus(Girard)Journal of Crustacean Biology4(2)252ndash260httpsdoiorg1011631937240x84x00363
Caplat P Cheptou P O Diez J Guisan A Larson B MMacDougall A S hellip Zhang R (2013) Movement impacts andmanagement of plant distributions in response to climate changeInsights from invasions Oikos 122(9) 1265ndash1274 httpsdoiorg101111j1600-0706201300430x
Chuang A amp Peterson C R (2016) Expanding population edgesTheories traits and trade-offsGlobal Change Biology22(2) 494ndash512httpsdoiorg101111gcb13107
ClarkJMKershnerMWampHolomuzkiJR(2008)Grainsizeandsorting effects on size-dependent responses by lotic crayfish tohigh flows Hydrobiologia 610 55ndash66 httpsdoiorg101007s10750-008-9422-0
CrandallKAampDeGraveS (2017)Anupdatedclassificationofthefreshwater crayfishes (Decapoda Astacidea) of the world with acompletespecieslistJournal of Crustacean Biology37(5)615ndash653httpsdoiorg101093jcbiolrux070
DavidsonAMJennionsMampNicotraAB(2011)Doinvasivespe-cies show higher phenotypic plasticity than native species and ifso is it adaptiveAmeta-analysisEcology Letters14(4) 419ndash431httpsdoiorg101111j1461-0248201101596x
DoddsWK Smith VH amp Lohman K (2002)Nitrogen and phos-phorusrelationshipstobenthicalgalbiomassintemperatestreamsCanadian Journal of Fisheries and Aquatic Sciences 59(5) 865ndash874httpsdoiorg101139f02-063
Fronhofer E A amp Altermatt F (2015) Eco-evolutionary feedbacksduring experimental range expansions Nature Communications 66844httpsdoiorg101038ncomms7844
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
Weconjecturethatashift intheselectionregimeexperiencedbyrustycrayfishfromcoretoleading-edgeareasisthemostprob-ableexplanationforthetrends inrelativechela lengthandweightobservedinthisstudyHoweverwithoutknowledgeoftheheritabil-ityofthecrayfishtraitsexaminedinthisstudyinferenceregardingthespecificmechanisms inoperation isstill limitedTheaccelerat-ingrateofspreadofrustycrayfish intheJDRthe lowpopulationdensities observedwithin several kilometres of the upstream anddownstreaminvasionfrontsandhighphysiologicalfitnessininva-sionfrontpopulationssuggestthatapushedinvasionexcludingsub-dominantcrayfishfromhigherdensityareasisunlikelytoexplaintheobservedtraitdifferencesMoreoverthereislittletonoevidenceoftheinfluenceofchelasizeorrelativebodyweightondispersalspeed(KamranampMoore 2015) Lastly the difference in relativeweightandchelalengthbetweeninvasioncoreandfrontpopulationscouldalsobedrivenbynaturalselectioninhighcrayfishdensitycorepop-ulationsHistoricaldatafromSorenson(2012)combinedwiththisstudy shownodifference inchela length (Supporting InformationFigureS51)butasignificantincreaseinrelativeweightfrom2010to2016atthepresumedsiteofrustycrayfishintroduction(SupportingInformationFigureS52)Thechangesintraitvaluesobservedherearethuslikelytobetheresultsofacombinationofdriversincludingreducedfitnessofcompetitivephenotypesatlowcrayfishdensityselectionforhighrelativeweightinthepopulationcoreandtrade-offsbetweenthesecompetitiveattributesandother traitsassoci-atedwithhigherdispersalability
Theobserved increase in rustycrayfishanabolicactivitymea-suredasRNADNAinleading-edgepopulationsoftheJDRalthoughweak in themainstem indicates that the rangeexpansionprocesshas led to greater somatic growth andor reproductive potentialin pioneer individuals This pattern matches several documentedincreases inbodyconditiongrowthandreproductivepotential insimilarstreaminvasionsbothwithinasingleinvasiongradientandbetweennativeandnon-nativepopulationsWithintheirnon-nativerange invasion front signal crayfish in Croatia and female spiny-cheekcrayfish in theDanubebothdisplayedgreater reproductivepotentials than their counterparts in core areas with the formeralsobeinginbetterconditionandenergeticstatus(Pacircrvulescuetal2015Rebrinaetal2015)Whencomparingnativeandnon-nativepopulationsofrustycrayfishbothlakeandmesocosmexperimentsfoundthatnon-nativeindividualshavehighergrowthratesandlevelsofactivitythantheirnativecongeners(PintorampSih2009Sargentamp Lodge 2014) Nonetheless whether the observed increase inrustycrayfishphysiologicalconditiontowardstheinvasionfront isassociated with greater somatic growth rates or gamete produc-tionremainsunresolvedandwarrantsfurtherinvestigationIndeed
simultaneous increases inconditiongrowthandreproductivepo-tentialarenotuniversalbecauseselectionfordispersalabilityduringrangeexpansionmay lead tounexpected trade-offsFor instancetadpolesandjuvenilesininvasionfrontpopulationsofcanetoadsintropicalAustraliagrowupto31fasterthanthosefromlongeres-tablishedpopulations(Phillips2009)andadultsdemonstratehigherfeeding rates larger fat stores andbetter condition thanconspe-cifics in later invasion stages (Brownetal2013)However lowerreproductiverateshavealsobeendocumentedincanetoadinvasionfrontpopulations(HudsonPhillipsBrownampShine2015)
Itmightseemthathighercrayfishgrowthratestowardstheinva-sionfrontscontradicttheobservedpatternsofreducedweightandchelalengthobservedinpioneercrayfishHoweverselectionforafasterlifestylecoulddecreaseageatmaturityandshortenthelifes-panoftheseinvasionfrontcrayfishwhileselectingagainstallome-tricgrowthofcompetitivemorphologyBothcrayfishgrowth rateandfecundityaredensitydependent(GuanampWiles1999MomotampGowing1977)Thereforeitispossiblethathighgrowthandfe-cundityphenotypeshavearisenfromnaturalselectioninthec 15 generationssincetheirintroductionaspartofadispersalsyndromeassociating rapid development and high fecunditywith dispersivetraits(RonceampClobert2012Stevensetal2013)
Rustycrayfishattheleadingedgesoftheirdistributionallimitsappeartobefeedinglowerinthefoodwebwhencomparedtocon-specifics locatedbehind the invasion frontThispattern stands incontradictionwithmostpreviousstudiesofstreaminvasionsRoundgobiesattheedgeoftheirexpandingrangeconsumemoreoftheirfavouredpreytypethanincentralpopulations(RabyGutowskyampFox2010)andhavehigherδ15Nsignaturesthanthepreviousyearfront(Brandneretal2013)Invasionfrontbloodyredmysidshrimp(Hemimysis anomala)werenotmoreselectiveintheirpreyconsump-tionbutshowedgreaterabilitytolocateandcapturezooplanktonprey than those shrimp in corepopulations (Iacarella etal 2015)ForcrayfishinvasionstrophicnicheshiftshaveonlybeenassessedatthebiogeographicalscaleandoffermixedinsightsInagreementwithourfindingsnon-nativepopulationsofrustycrayfishandvirilecrayfish(Faxonius virilis)appearedtoshowgreaterratesofalgaecon-sumption (despite constant macroinvertebrate prey consumption)thandidnativepopulationsinlaboratoryassays(Glonetal2018)By contrast an intercontinental stable isotope analysis revealedtrophicnicheconservatisminsignalcrayfishbetweenitsnativeandnon-native range (LarsonOldenampUsio 2010) Trophic flexibilityhasbeenshowntobespecies-dependenteveninsympatricnativecrayfishspecies (JohnstonRobsonampFairweather2011)andmaythus not be a consistent characteristic among invasive omnivoreseitherItisunlikelythatcannibalismawidespreadphenomenonincrayfishpopulations(GuanampWiles1998) ledtotheobservedin-creaseintrophicpositioninareaswithhighdensitiesofcrayfishasconspecificdensitywasnotcorrelatedtotrophicpositionintheJDR(Figure4SupportingInformationAppendixS3)Lastlyitisunlikelythatnon-crayfishpredatorsandcompetitorscouldhavedriventhisdownwardshiftinthetrophicpositionofrustycrayfishasthisshiftwasobservedacrossboththedownstream(increasingfishdensity)
Rustycrayfishhada lower trophicpositionevenwhenmacro-invertebrateprey availability increased towards the invasion frontintheNorthForkJDRThispatterncontrastedwithpastevidenceof a positive relationship between macroinvertebrate availabilityand crayfish trophic position (Olsson etal 2008) and greater as-similation efficiencies of invertebrates than other food items bycrayfish (WhitledgeampRabeni 1997)However the lackof signifi-cantdecreaseintrophicpositiontowardstheinvasionfront intheSouth Fork JDR could be due to a counter-effect from increasingmacroinvertebrate biomass upstream Consumption of macroin-vertebrateshasbeen linkedto increases inweightgainandmeta-bolicrates(BondarBottriellZeronampRichardson2005Hilletal1993 McFeeters Xenopoulos Spooner Wagner amp Frost 2011)Nevertheless in these same studies juvenile signal crayfish in anatural settingdisproportionatelyconsumedfoodtypes thatweretheoppositeofthoseshowntobeofmostnutritionalvaluetothem(Bondar etal 2005) and rusty crayfishmortalitywashigheron adietbasedoninvertebratethanoneonperiphytonordetritus(Hilletal 1993) This suggests that high growth might be associatedwith greater physiological stress due tomore frequentmoultingandhigherforagingcostsinnaturalsettingsThuswehypothesisethatenergyintakeandlong-termfitnessofrustycrayfishassociatedwithperiphytonanddetritusconsumptionmaybehigherthanwithmacroinvertebratedietsdespitetheir lowerdigestionefficiencyoftheseresources
Trade-offs can also arise between increased dispersal rates atrangemarginsand the functional responseof thenon-nativecon-sumer due to the high cost of dispersal (Fronhofer amp Altermatt2015)Giventheircurrentrateofspread(c20kmyeardownstreamfrom2010to2016)intheJDR(MessagerampOlden2018)andawin-dowofactivityof8ndash9months(basedonwatertemperaturesinthemainstem)rustycrayfishwouldhavetoachieveanetdownstreamspreadrateof80mdayonaveragewithoutconsideringtimeded-icatedtomatingandjuvenileparentalcareWespeculatethatthispacecouldrestricttheamountoftimeavailableforactivelypreyingoninvertebratesandcouldselectforthosecrayfishbestabletoef-ficientlyfeedandgrowonabundantandaccessiblebasalresourcesIthasalsobeenhypothesisedforstreamfishesthatthosenon-nativespeciesthatcansustaingrowthandreproductiononlow-qualityre-sourcesshouldbebestabletobecomeestablished(GidoampFranssen2007) Incrayfishabroader trophicniche thatexpandedtowardslower trophic levelsmayhaveaffordedcompetitiveadvantages totheintroducedsignalcrayfishoverthenativenoblecrayfishAstacus astacus inSwedishstreams (OlssonStenrothNystromampGraneli2009) Therefore our findings that rusty crayfish at the invasionfrontactmostlyasprimaryconsumerswhileachievinggreaterphys-iologicalconditionmightreflectanincreaseinfeedingefficiencyonbasal resources as a by-product of greater dispersal ability devel-opedthroughtheirrangeexpansionintheJDR
a crucial first step towards developing spatially explicit strategiestocontrol this invasion If thedocumentedphenotypicshifts fromcore to invasion front populations are indeed associatedwith theaccelerating rateof spreadof rusty crayfish then targeting thoseindividualsattheinvasionleadingedgeforremoval(egbytrapping)mightconstraintheaccumulationofdispersivephenotypesintheseareasAccountingforthesephenotypicshiftsinmechanisticmodelsofinvasivespread(egMessagerampOlden2018)couldalsoprovideuswithavirtual laboratorytotesttheeffectivenessofalternativecontrolstrategiesincontainingthespreadofriverineinvaderssuchasrustycrayfish
Our results suggest that low conspecific densities and spatialsortinginleading-edgepopulationsledtoashift inthephenotypeofrustycrayfishtowards lowercompetitiveabilityhigher intrinsicgrowthandorreproductionandgreaterforagingefficiencyonbasalresourcesastheyspreadupstreamanddownstreamintheJDROurstudydesignenabledustolinkmorphologicalandfunctionaltraitstobetterexploretheconsequencesofthisrangeexpansiononinvadedecosystemsWeexpectthatthediminishedcompetitiveabilityob-servedinthevanguardofthisrustycrayfishinvasionmightleadtoreducedfitnessoftheinvasionfrontphenotypesoncedensities innewlycolonisedareas limit theavailabilityofshelterand intensifycompetition formatesThe long-termevolutionary implicationsofthesephenotypicshiftsmightthusbelimited(PerkinsBoettigerampPhillips2016)Howeverthetrophicshiftobservedininvasionfrontpopulationscouldalsoallowrustycrayfishtoreachhigherdensitiesintheseareasastheymightexploitresourcesmorebroadlyandeffi-cientlyundercompetitiveconditionsTheevolutionaryforcesatplayinthisinvasionhaveprobablyinteractedwithlongitudinalgradientsinenvironmentalconditionsinwaysanalogoustothoseexperiencedbyspeciesduringtheirmigrationtowardscoolerareasunderclimatechangeIntegratingthestudyofmorphologicalandfunctionaltraitswith spatial variation in environmental conditions thus provides arobustwaytoassesswhethercontemporaryevolutionisalteringthephenotypeandecosystemimpactsofspeciesastheirrangeexpandsthroughthelandscape
Inconclusionthisstudyaddsevidenceinsupportofphenotypicchangesexpectedinnon-nativeorganismsexposedtochangingse-lectionpressuresas they invadenewenvironmentsDisentanglingthe causes of these changes whether related to environmentalfactorsorselectionduetorangeexpansionremainsan importantareaofinvestigationasweseektobetterunderstandtheecologicalimpactsofinvasivespeciesandhownativespecieswillrespondtoshiftingenvironmentalconditionsinthefuture
ACKNOWLEDG MENTS
WethankJeffAdamsEricLarsonDavidWoosterStephenBollensandKeithSorensonforprovidinghistoricaldataforrustycrayfishthe staff at theGrantCountyAssessorsoffice and the JohnDayFossilBedsNationalMonument for their help accessing the riverParticular appreciation goes to all the landowners throughout theJohnDayRiverbasin foraccess to their landandsupport for this
12emsp |emsp emspensp MESSAGER And OLdEn
projectWearegratefultoJacobCrunkforhisinestimablehelpwithfieldworkandEthenWhattamforhishelpprocessingmacroinver-tebratesamplesFromtheUniversityofWashingtonwethanktheMolecularEcologyResearchLaboratory(MERLab)andmorespecifi-callyIsadoraJimenez-HidalgoandNatalieLowelltheOldenlabaswellasJoshuaLawlerThomasQuinnandPatrickTobinThemanu-scriptwasimprovedbythecommentsfromtwoanonymousreview-ersFundingsupportwasprovidedbytheJohnNCobbScholarshipin Fisheries the Simpson Award from the Society for FreshwaterScienceandtheCrustaceanSocietyfellowshipinGraduateStudiesawarded to MLM and the University of Washington H MasonKeelerEndowedProfessorshipawardtoJDO
Mathis L Messager httpsorcidorg0000-0002-3051-8068
Julian D Olden httpsorcidorg0000-0003-2143-1187
R E FE R E N C E S
AndersonCampCabanaG (2007)Estimatingthetrophicpositionofaquatic consumers in river food webs using stable nitrogen iso-topes Journal of the North American Benthological Society 26(2)273ndash285 httpsdoiorg1018990887-3593(2007)26[273ettpoa]20co2
Arrington D A ampWinemiller K O (2002) Preservation effects onstable isotope analysis of fishmuscleTransactions of the American Fisheries Society131(2)337ndash342httpsdoiorg1015771548-8659(2002)131lt0337peosiagt20co2
Berdalet E Roldaacuten C ampOlivarM P (2005) Quantifying RNA andDNAinplanktonicorganismswithSYBRGreenIIandnucleasesPartBQuantification in natural samplesScientia Marina69(1) 17ndash30httpsdoiorg103989scimar200569n117
BerdaletERoldaacutenCOlivarMPampLysnesK (2005)QuantifyingRNAandDNAinplanktonicorganismswithSYBRGreenIIandnu-cleases Part A Optimisation of the assay Scientia Marina 69(1)1ndash16httpsdoiorg103989scimar200569n11
Bobeldyk A M amp Lamberti G A (2010) Stream food web re-sponses to a large omnivorous invader Orconectes rusticus (Decapoda Cambaridae) Crustaceana 83(6) 641ndash657 httpsdoiorg101163001121610x491031
BondarCABottriellKZeronKampRichardsonJS(2005)Doestro-phicpositionof theomnivoroussignalcrayfish (Pacifastacus lenius-culus) inastreamfoodwebvarywith lifehistorystageordensityCanadian Journal of Fisheries and Aquatic Sciences62(11)2632ndash2639httpsdoiorg101139f05-167
BrandnerJCerwenkaAFSchliewenUKampGeistJ(2013)BiggerisbetterCharacteristicsofroundgobiesforminganinvasionfrontinthe Danube River PLoS ONE8(9)e73036httpsdoiorg101371journalpone0073036
BrownGPKelehearCampShineR (2013)Theearly toadgets theworm Cane toads at an invasion front benefit from higher preyavailability Journal of Animal Ecology 82(4) 854ndash862 httpsdoiorg1011111365-265612048
Burton O J Phillips B L amp Travis J M J (2010) Trade-offs and the evolution of life-histories during range ex-pansion Ecology Letters 13(10) 1210ndash1220 httpsdoiorg101111j1461-0248201001505x
Capelli G M amp Hamilton P A (1984) Effects of food shelter andtimeof dayon aggressive activity in the crayfishOrconectes rusti-cus(Girard)Journal of Crustacean Biology4(2)252ndash260httpsdoiorg1011631937240x84x00363
Caplat P Cheptou P O Diez J Guisan A Larson B MMacDougall A S hellip Zhang R (2013) Movement impacts andmanagement of plant distributions in response to climate changeInsights from invasions Oikos 122(9) 1265ndash1274 httpsdoiorg101111j1600-0706201300430x
Chuang A amp Peterson C R (2016) Expanding population edgesTheories traits and trade-offsGlobal Change Biology22(2) 494ndash512httpsdoiorg101111gcb13107
ClarkJMKershnerMWampHolomuzkiJR(2008)Grainsizeandsorting effects on size-dependent responses by lotic crayfish tohigh flows Hydrobiologia 610 55ndash66 httpsdoiorg101007s10750-008-9422-0
CrandallKAampDeGraveS (2017)Anupdatedclassificationofthefreshwater crayfishes (Decapoda Astacidea) of the world with acompletespecieslistJournal of Crustacean Biology37(5)615ndash653httpsdoiorg101093jcbiolrux070
DavidsonAMJennionsMampNicotraAB(2011)Doinvasivespe-cies show higher phenotypic plasticity than native species and ifso is it adaptiveAmeta-analysisEcology Letters14(4) 419ndash431httpsdoiorg101111j1461-0248201101596x
DoddsWK Smith VH amp Lohman K (2002)Nitrogen and phos-phorusrelationshipstobenthicalgalbiomassintemperatestreamsCanadian Journal of Fisheries and Aquatic Sciences 59(5) 865ndash874httpsdoiorg101139f02-063
Fronhofer E A amp Altermatt F (2015) Eco-evolutionary feedbacksduring experimental range expansions Nature Communications 66844httpsdoiorg101038ncomms7844
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
Rustycrayfishhada lower trophicpositionevenwhenmacro-invertebrateprey availability increased towards the invasion frontintheNorthForkJDRThispatterncontrastedwithpastevidenceof a positive relationship between macroinvertebrate availabilityand crayfish trophic position (Olsson etal 2008) and greater as-similation efficiencies of invertebrates than other food items bycrayfish (WhitledgeampRabeni 1997)However the lackof signifi-cantdecreaseintrophicpositiontowardstheinvasionfront intheSouth Fork JDR could be due to a counter-effect from increasingmacroinvertebrate biomass upstream Consumption of macroin-vertebrateshasbeen linkedto increases inweightgainandmeta-bolicrates(BondarBottriellZeronampRichardson2005Hilletal1993 McFeeters Xenopoulos Spooner Wagner amp Frost 2011)Nevertheless in these same studies juvenile signal crayfish in anatural settingdisproportionatelyconsumedfoodtypes thatweretheoppositeofthoseshowntobeofmostnutritionalvaluetothem(Bondar etal 2005) and rusty crayfishmortalitywashigheron adietbasedoninvertebratethanoneonperiphytonordetritus(Hilletal 1993) This suggests that high growth might be associatedwith greater physiological stress due tomore frequentmoultingandhigherforagingcostsinnaturalsettingsThuswehypothesisethatenergyintakeandlong-termfitnessofrustycrayfishassociatedwithperiphytonanddetritusconsumptionmaybehigherthanwithmacroinvertebratedietsdespitetheir lowerdigestionefficiencyoftheseresources
Trade-offs can also arise between increased dispersal rates atrangemarginsand the functional responseof thenon-nativecon-sumer due to the high cost of dispersal (Fronhofer amp Altermatt2015)Giventheircurrentrateofspread(c20kmyeardownstreamfrom2010to2016)intheJDR(MessagerampOlden2018)andawin-dowofactivityof8ndash9months(basedonwatertemperaturesinthemainstem)rustycrayfishwouldhavetoachieveanetdownstreamspreadrateof80mdayonaveragewithoutconsideringtimeded-icatedtomatingandjuvenileparentalcareWespeculatethatthispacecouldrestricttheamountoftimeavailableforactivelypreyingoninvertebratesandcouldselectforthosecrayfishbestabletoef-ficientlyfeedandgrowonabundantandaccessiblebasalresourcesIthasalsobeenhypothesisedforstreamfishesthatthosenon-nativespeciesthatcansustaingrowthandreproductiononlow-qualityre-sourcesshouldbebestabletobecomeestablished(GidoampFranssen2007) Incrayfishabroader trophicniche thatexpandedtowardslower trophic levelsmayhaveaffordedcompetitiveadvantages totheintroducedsignalcrayfishoverthenativenoblecrayfishAstacus astacus inSwedishstreams (OlssonStenrothNystromampGraneli2009) Therefore our findings that rusty crayfish at the invasionfrontactmostlyasprimaryconsumerswhileachievinggreaterphys-iologicalconditionmightreflectanincreaseinfeedingefficiencyonbasal resources as a by-product of greater dispersal ability devel-opedthroughtheirrangeexpansionintheJDR
a crucial first step towards developing spatially explicit strategiestocontrol this invasion If thedocumentedphenotypicshifts fromcore to invasion front populations are indeed associatedwith theaccelerating rateof spreadof rusty crayfish then targeting thoseindividualsattheinvasionleadingedgeforremoval(egbytrapping)mightconstraintheaccumulationofdispersivephenotypesintheseareasAccountingforthesephenotypicshiftsinmechanisticmodelsofinvasivespread(egMessagerampOlden2018)couldalsoprovideuswithavirtual laboratorytotesttheeffectivenessofalternativecontrolstrategiesincontainingthespreadofriverineinvaderssuchasrustycrayfish
Our results suggest that low conspecific densities and spatialsortinginleading-edgepopulationsledtoashift inthephenotypeofrustycrayfishtowards lowercompetitiveabilityhigher intrinsicgrowthandorreproductionandgreaterforagingefficiencyonbasalresourcesastheyspreadupstreamanddownstreamintheJDROurstudydesignenabledustolinkmorphologicalandfunctionaltraitstobetterexploretheconsequencesofthisrangeexpansiononinvadedecosystemsWeexpectthatthediminishedcompetitiveabilityob-servedinthevanguardofthisrustycrayfishinvasionmightleadtoreducedfitnessoftheinvasionfrontphenotypesoncedensities innewlycolonisedareas limit theavailabilityofshelterand intensifycompetition formatesThe long-termevolutionary implicationsofthesephenotypicshiftsmightthusbelimited(PerkinsBoettigerampPhillips2016)Howeverthetrophicshiftobservedininvasionfrontpopulationscouldalsoallowrustycrayfishtoreachhigherdensitiesintheseareasastheymightexploitresourcesmorebroadlyandeffi-cientlyundercompetitiveconditionsTheevolutionaryforcesatplayinthisinvasionhaveprobablyinteractedwithlongitudinalgradientsinenvironmentalconditionsinwaysanalogoustothoseexperiencedbyspeciesduringtheirmigrationtowardscoolerareasunderclimatechangeIntegratingthestudyofmorphologicalandfunctionaltraitswith spatial variation in environmental conditions thus provides arobustwaytoassesswhethercontemporaryevolutionisalteringthephenotypeandecosystemimpactsofspeciesastheirrangeexpandsthroughthelandscape
Inconclusionthisstudyaddsevidenceinsupportofphenotypicchangesexpectedinnon-nativeorganismsexposedtochangingse-lectionpressuresas they invadenewenvironmentsDisentanglingthe causes of these changes whether related to environmentalfactorsorselectionduetorangeexpansionremainsan importantareaofinvestigationasweseektobetterunderstandtheecologicalimpactsofinvasivespeciesandhownativespecieswillrespondtoshiftingenvironmentalconditionsinthefuture
ACKNOWLEDG MENTS
WethankJeffAdamsEricLarsonDavidWoosterStephenBollensandKeithSorensonforprovidinghistoricaldataforrustycrayfishthe staff at theGrantCountyAssessorsoffice and the JohnDayFossilBedsNationalMonument for their help accessing the riverParticular appreciation goes to all the landowners throughout theJohnDayRiverbasin foraccess to their landandsupport for this
12emsp |emsp emspensp MESSAGER And OLdEn
projectWearegratefultoJacobCrunkforhisinestimablehelpwithfieldworkandEthenWhattamforhishelpprocessingmacroinver-tebratesamplesFromtheUniversityofWashingtonwethanktheMolecularEcologyResearchLaboratory(MERLab)andmorespecifi-callyIsadoraJimenez-HidalgoandNatalieLowelltheOldenlabaswellasJoshuaLawlerThomasQuinnandPatrickTobinThemanu-scriptwasimprovedbythecommentsfromtwoanonymousreview-ersFundingsupportwasprovidedbytheJohnNCobbScholarshipin Fisheries the Simpson Award from the Society for FreshwaterScienceandtheCrustaceanSocietyfellowshipinGraduateStudiesawarded to MLM and the University of Washington H MasonKeelerEndowedProfessorshipawardtoJDO
Mathis L Messager httpsorcidorg0000-0002-3051-8068
Julian D Olden httpsorcidorg0000-0003-2143-1187
R E FE R E N C E S
AndersonCampCabanaG (2007)Estimatingthetrophicpositionofaquatic consumers in river food webs using stable nitrogen iso-topes Journal of the North American Benthological Society 26(2)273ndash285 httpsdoiorg1018990887-3593(2007)26[273ettpoa]20co2
Arrington D A ampWinemiller K O (2002) Preservation effects onstable isotope analysis of fishmuscleTransactions of the American Fisheries Society131(2)337ndash342httpsdoiorg1015771548-8659(2002)131lt0337peosiagt20co2
Berdalet E Roldaacuten C ampOlivarM P (2005) Quantifying RNA andDNAinplanktonicorganismswithSYBRGreenIIandnucleasesPartBQuantification in natural samplesScientia Marina69(1) 17ndash30httpsdoiorg103989scimar200569n117
BerdaletERoldaacutenCOlivarMPampLysnesK (2005)QuantifyingRNAandDNAinplanktonicorganismswithSYBRGreenIIandnu-cleases Part A Optimisation of the assay Scientia Marina 69(1)1ndash16httpsdoiorg103989scimar200569n11
Bobeldyk A M amp Lamberti G A (2010) Stream food web re-sponses to a large omnivorous invader Orconectes rusticus (Decapoda Cambaridae) Crustaceana 83(6) 641ndash657 httpsdoiorg101163001121610x491031
BondarCABottriellKZeronKampRichardsonJS(2005)Doestro-phicpositionof theomnivoroussignalcrayfish (Pacifastacus lenius-culus) inastreamfoodwebvarywith lifehistorystageordensityCanadian Journal of Fisheries and Aquatic Sciences62(11)2632ndash2639httpsdoiorg101139f05-167
BrandnerJCerwenkaAFSchliewenUKampGeistJ(2013)BiggerisbetterCharacteristicsofroundgobiesforminganinvasionfrontinthe Danube River PLoS ONE8(9)e73036httpsdoiorg101371journalpone0073036
BrownGPKelehearCampShineR (2013)Theearly toadgets theworm Cane toads at an invasion front benefit from higher preyavailability Journal of Animal Ecology 82(4) 854ndash862 httpsdoiorg1011111365-265612048
Burton O J Phillips B L amp Travis J M J (2010) Trade-offs and the evolution of life-histories during range ex-pansion Ecology Letters 13(10) 1210ndash1220 httpsdoiorg101111j1461-0248201001505x
Capelli G M amp Hamilton P A (1984) Effects of food shelter andtimeof dayon aggressive activity in the crayfishOrconectes rusti-cus(Girard)Journal of Crustacean Biology4(2)252ndash260httpsdoiorg1011631937240x84x00363
Caplat P Cheptou P O Diez J Guisan A Larson B MMacDougall A S hellip Zhang R (2013) Movement impacts andmanagement of plant distributions in response to climate changeInsights from invasions Oikos 122(9) 1265ndash1274 httpsdoiorg101111j1600-0706201300430x
Chuang A amp Peterson C R (2016) Expanding population edgesTheories traits and trade-offsGlobal Change Biology22(2) 494ndash512httpsdoiorg101111gcb13107
ClarkJMKershnerMWampHolomuzkiJR(2008)Grainsizeandsorting effects on size-dependent responses by lotic crayfish tohigh flows Hydrobiologia 610 55ndash66 httpsdoiorg101007s10750-008-9422-0
CrandallKAampDeGraveS (2017)Anupdatedclassificationofthefreshwater crayfishes (Decapoda Astacidea) of the world with acompletespecieslistJournal of Crustacean Biology37(5)615ndash653httpsdoiorg101093jcbiolrux070
DavidsonAMJennionsMampNicotraAB(2011)Doinvasivespe-cies show higher phenotypic plasticity than native species and ifso is it adaptiveAmeta-analysisEcology Letters14(4) 419ndash431httpsdoiorg101111j1461-0248201101596x
DoddsWK Smith VH amp Lohman K (2002)Nitrogen and phos-phorusrelationshipstobenthicalgalbiomassintemperatestreamsCanadian Journal of Fisheries and Aquatic Sciences 59(5) 865ndash874httpsdoiorg101139f02-063
Fronhofer E A amp Altermatt F (2015) Eco-evolutionary feedbacksduring experimental range expansions Nature Communications 66844httpsdoiorg101038ncomms7844
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
12emsp |emsp emspensp MESSAGER And OLdEn
projectWearegratefultoJacobCrunkforhisinestimablehelpwithfieldworkandEthenWhattamforhishelpprocessingmacroinver-tebratesamplesFromtheUniversityofWashingtonwethanktheMolecularEcologyResearchLaboratory(MERLab)andmorespecifi-callyIsadoraJimenez-HidalgoandNatalieLowelltheOldenlabaswellasJoshuaLawlerThomasQuinnandPatrickTobinThemanu-scriptwasimprovedbythecommentsfromtwoanonymousreview-ersFundingsupportwasprovidedbytheJohnNCobbScholarshipin Fisheries the Simpson Award from the Society for FreshwaterScienceandtheCrustaceanSocietyfellowshipinGraduateStudiesawarded to MLM and the University of Washington H MasonKeelerEndowedProfessorshipawardtoJDO
Mathis L Messager httpsorcidorg0000-0002-3051-8068
Julian D Olden httpsorcidorg0000-0003-2143-1187
R E FE R E N C E S
AndersonCampCabanaG (2007)Estimatingthetrophicpositionofaquatic consumers in river food webs using stable nitrogen iso-topes Journal of the North American Benthological Society 26(2)273ndash285 httpsdoiorg1018990887-3593(2007)26[273ettpoa]20co2
Arrington D A ampWinemiller K O (2002) Preservation effects onstable isotope analysis of fishmuscleTransactions of the American Fisheries Society131(2)337ndash342httpsdoiorg1015771548-8659(2002)131lt0337peosiagt20co2
Berdalet E Roldaacuten C ampOlivarM P (2005) Quantifying RNA andDNAinplanktonicorganismswithSYBRGreenIIandnucleasesPartBQuantification in natural samplesScientia Marina69(1) 17ndash30httpsdoiorg103989scimar200569n117
BerdaletERoldaacutenCOlivarMPampLysnesK (2005)QuantifyingRNAandDNAinplanktonicorganismswithSYBRGreenIIandnu-cleases Part A Optimisation of the assay Scientia Marina 69(1)1ndash16httpsdoiorg103989scimar200569n11
Bobeldyk A M amp Lamberti G A (2010) Stream food web re-sponses to a large omnivorous invader Orconectes rusticus (Decapoda Cambaridae) Crustaceana 83(6) 641ndash657 httpsdoiorg101163001121610x491031
BondarCABottriellKZeronKampRichardsonJS(2005)Doestro-phicpositionof theomnivoroussignalcrayfish (Pacifastacus lenius-culus) inastreamfoodwebvarywith lifehistorystageordensityCanadian Journal of Fisheries and Aquatic Sciences62(11)2632ndash2639httpsdoiorg101139f05-167
BrandnerJCerwenkaAFSchliewenUKampGeistJ(2013)BiggerisbetterCharacteristicsofroundgobiesforminganinvasionfrontinthe Danube River PLoS ONE8(9)e73036httpsdoiorg101371journalpone0073036
BrownGPKelehearCampShineR (2013)Theearly toadgets theworm Cane toads at an invasion front benefit from higher preyavailability Journal of Animal Ecology 82(4) 854ndash862 httpsdoiorg1011111365-265612048
Burton O J Phillips B L amp Travis J M J (2010) Trade-offs and the evolution of life-histories during range ex-pansion Ecology Letters 13(10) 1210ndash1220 httpsdoiorg101111j1461-0248201001505x
Capelli G M amp Hamilton P A (1984) Effects of food shelter andtimeof dayon aggressive activity in the crayfishOrconectes rusti-cus(Girard)Journal of Crustacean Biology4(2)252ndash260httpsdoiorg1011631937240x84x00363
Caplat P Cheptou P O Diez J Guisan A Larson B MMacDougall A S hellip Zhang R (2013) Movement impacts andmanagement of plant distributions in response to climate changeInsights from invasions Oikos 122(9) 1265ndash1274 httpsdoiorg101111j1600-0706201300430x
Chuang A amp Peterson C R (2016) Expanding population edgesTheories traits and trade-offsGlobal Change Biology22(2) 494ndash512httpsdoiorg101111gcb13107
ClarkJMKershnerMWampHolomuzkiJR(2008)Grainsizeandsorting effects on size-dependent responses by lotic crayfish tohigh flows Hydrobiologia 610 55ndash66 httpsdoiorg101007s10750-008-9422-0
CrandallKAampDeGraveS (2017)Anupdatedclassificationofthefreshwater crayfishes (Decapoda Astacidea) of the world with acompletespecieslistJournal of Crustacean Biology37(5)615ndash653httpsdoiorg101093jcbiolrux070
DavidsonAMJennionsMampNicotraAB(2011)Doinvasivespe-cies show higher phenotypic plasticity than native species and ifso is it adaptiveAmeta-analysisEcology Letters14(4) 419ndash431httpsdoiorg101111j1461-0248201101596x
DoddsWK Smith VH amp Lohman K (2002)Nitrogen and phos-phorusrelationshipstobenthicalgalbiomassintemperatestreamsCanadian Journal of Fisheries and Aquatic Sciences 59(5) 865ndash874httpsdoiorg101139f02-063
Fronhofer E A amp Altermatt F (2015) Eco-evolutionary feedbacksduring experimental range expansions Nature Communications 66844httpsdoiorg101038ncomms7844
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
emspensp emsp | emsp13MESSAGER And OLdEn
GidoKBampFranssenNR(2007)InvasionofstreamfishesintolowtrophicpositionsEcology of Freshwater Fish16(3)457ndash464httpsdoiorg101111j1600-0633200700235x
GlonMG Larson E RampPangle K L (2015) Comparison of 13Cand 15N discrimination factors and turnover rates between con-generic crayfish Orconectes rusticus and O virilis (DecapodaCambaridae)Hydrobiologia768(1)51ndash61httpsdoiorg101007s10750-015-2527-3
GlonMGReisinger L SampPintor LM (2018)Biogeographicdif-ferences between native and non-native populations of crayfishalter species coexistence and trophic interactions in mesocosmsBiological Invasions 20(12) 3475ndash3490 httpsdoiorg101007s10530-018-1788-y
GuanRampWiles PR (1998) Feeding ecologyof the signal crayfishPacifastacus leniusculusinaBritishlowlandriverAquaculture169(3ndash4)177ndash193httpsdoiorg101016s0044-8486(98)00377-9
Guan R amp Wiles P R (1999) Growth and reproduction of the in-troduced crayfish Pacifastacus leniusculus in a British lowlandriver Fisheries Research 42(3) 245ndash259 httpsdoiorg101016s0165-7836(99)00044-2
HamrP(1999)The potential for the commercial harvest of the exotic rusty crayfish (Orconectes rusticus) A feasibility study Keene ON OWCrayfishEnterprises
HansenGJVanderZandenMJBlumMJClaytonMKHainEFHauxwell JhellipNilssonE (2013)Commonly rareand rarelycommon Comparing population abundance of invasive and nativesquatic speciesPLoS ONE8(10) e77415httpsdoiorg101371journalpone0077415
Hill AM SinarsDMamp LodgeDM (1993) Invasion of an occu-piednichebythecrayfishOrconectes rusticus-potentialimportanceof growth and mortality Oecologia 94(3) 303ndash306 httpsdoiorg101007bf00317102
HudinaSHockKŽganecKampLucićA (2012)Changes inpopu-lation characteristics and structure of the signal crayfish at theedgeofitsinvasiverangeinaEuropeanriverAnnales de Limnologie ndash International Journal of Limnology 48(1) 3ndash11 httpsdoiorg101051limn2011051
HudinaSZganecKampHockK(2015)Differencesinaggressivebe-haviour along the expanding range of an invasive crayfishAn im-portantcomponentofinvasiondynamicsBiological Invasions17(11)3101ndash3112httpsdoiorg101007s10530-015-0936-x
HudsonCMPhillipsB LBrownGPampShineR (2015)Virginsin the vanguard Low reproductive frequency in invasion-frontcanetoadsBiological Journal of the Linnean Society116(4)743ndash747httpsdoiorg101111bij12618
IacarellaJCDickJTAampRicciardiA(2015)Aspatio-temporalcon-trastofthepredatoryimpactofaninvasivefreshwatercrustaceanDiversity and Distributions21(7)803ndash812httpsdoiorg101111ddi12318
JohnstonKRobsonBJampFairweatherPG(2011)Trophicpositionsof omnivores are not always flexible Evidence from four speciesof freshwater crayfishAustral Ecology36(3) 269ndash279 httpsdoiorg101111j1442-9993201002147x
KahlertM ampMcKie B G (2014) Comparing new and conventionalmethods to estimate benthic algal biomass and composition infreshwaters Environmental Science Processes amp Impacts 16(11)2627ndash2634
KamranMampMoore PA (2015) Comparative homing behaviors intwospeciesofcrayfishFallicambarus oodiens and Orconectes rusti-cus Ethology121(8)775ndash784httpsdoiorg101111eth12392
usefulmeasure for ecological health assessment andexperimentalecology Aquatic Ecology 45(4) 547ndash559 httpsdoiorg101007s10452-011-9375-7
Laparie M Renault D Lebouvier M amp Delattre T (2013) Is dis-persalpromotedat the invasionfrontMorphologicalanalysisofaground beetle invading the Kerguelen IslandsMerizodus soledadi-nus (ColeopteraCarabidae)Biological Invasions15(8) 1641ndash1648httpsdoiorg101007s10530-012-0403-x
LarsonERampOldenJD(2016)FieldsamplingtechniquesforcrayfishInMLongshawampPStebbing(Eds)Biology and ecology of crayfish(pp287ndash323)BocaRatonFLCRCPresshttpsdoiorg101201b20073
LodgeDMDeinesAGherardiFYeoDCArcellaTBaldridgeAKhellipHowardGW (2012)Global introductionsof crayfishesEvaluating the impact of species invasions on ecosystem servicesAnnual Review of Ecology Evolution and Systematics 43 449ndash472httpsdoiorg101146annurev-ecolsys-111511-103919
LormanJG(1980)Ecology of the crayfish Orconectes rusticus in Northern Wisconsin(PhD)UniversityofWisconsin-MadisonMadisonWI
MasonWTLewisPAampWeberCI(1983)AnevaluationofbenthicmacroinvertebratebiomassmethodologyEnvironmental Monitoring and Assessment3(1)29ndash44httpsdoiorg101007bf00394030
MatherMEampSteinRA (1993)Usinggrowthmortalitytrade-offstoexploreacrayfishspeciesreplacementinstreamrifflesandpoolsCanadian Journal of Fisheries and Aquatic Sciences 50(1) 88ndash96httpsdoiorg101139f93-011
McFeetersB J XenopoulosMA SpoonerD EWagnerNDampFrostPC(2011)Intraspecificmass-scalingoffieldmetabolicratesof a freshwater crayfish varies with stream land cover Ecosphere2(2)1ndash10httpsdoiorg101890es10-001121
MessagerMLampOldenJD(2018)Individual-basedmodelsforecastthespreadandinformthemanagementofanemergingriverinein-vader Diversity and Distributions 24(12) 1816ndash1829 httpsdoiorg101111ddi12829
MomotWTampGowingH(1977)ProductionandpopulationdynamicsofthecrayfishOrconectes virilis inthreeMichiganLakesJournal of the Fisheries Research Board of Canada34(11)2030ndash2040httpsdoiorg101139f77-272
MoranEVampAlexanderJM(2014)Evolutionaryresponsestoglobalchange Lessons from invasive speciesEcology Letters17(5) 637ndash649httpsdoiorg101111ele12262
MundahlNDampBentonMJ(1990)Aspectsofthethermalecologyof the rusty crayfishOrconectes rusticus (Girard)Oecologia 82(2)210ndash216httpsdoiorgdoi101007Bf00323537
Olden J D Adams J W amp Larson E R (2009) First record ofOrconectes rusticus (Girard1852) (DecapodaCambaridae)westoftheGreatContinentalDivideinNorthAmericaCrustaceana82(10)1347ndash1351
OlssonKNystromPStenrothPNilssonESvenssonMampGraneliW (2008) The influence of food quality and availability on tro-phicpositioncarbonsignatureandgrowth rateofanomnivorous
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
SorensonK L (2012)Comparative population biology of native and in-vasive crayfish in the John Day River Oregon USA(MS)WashingtonStateUniversityPullmanWARetrievedfromhttpsbooksgooglecombooksid=0zbmoAEACAAJ
Stevens VM Trochet A Blanchet SMoulherat S Clobert J ampBaguetteM(2013)Dispersalsyndromesandtheuseoflife-historiestopredictdispersalEvolutionary Applications6(4)630ndash642httpsdoiorg101111eva12049
ThomsenMSOldenJDWernbergTGriffinJNampSillimanBR (2011) A broad framework to organize and compare ecologicalinvasionimpactsEnvironmental Research111(7)899ndash908httpsdoiorg101016jenvres201105024
Travis J M J Delgado M Bocedi G Baguette M Barton KBonte D hellip Bullock J M (2013) Dispersal and speciesrsquo re-sponses to climate changeOikos122(11)1532ndash1540httpsdoiorg101111j1600-0706201300399x
Vrede T Persson J amp Aronsen G (2002) The influence of foodquality (P C ratio)onRNADNAratioandsomaticgrowth rateofDaphnia Limnology and Oceanography47(2) 487ndash494 httpsdoiorg104319lo20024720487
Weiss-Lehman C Hufbauer R A ampMelbourne B A (2017) Rapidtrait evolution drives increased speed and variance in experimen-talrangeexpansionsNature Communications814303httpsdoiorg101038ncomms14303
WhitledgeGWampRabeniCF(1997)EnergysourcesandecologicalroleofcrayfishesinanOzarkstreamInsightsfromstableisotopesandgutanalysisCanadian Journal of Fisheries and Aquatic Sciences54(11)2555ndash2563httpsdoiorg101139f97-173
SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
14emsp |emsp emspensp MESSAGER And OLdEn
crayfishCanadian Journal of Fisheries and Aquatic Sciences 65(10)2293ndash2304httpsdoiorg101139f08-137
Pacircrvulescu L PicircrvuMMoroşan L amp Zaharia C (2015) Plasticityin fecundityhighlights the femalesrsquo importance in the spiny-cheekcrayfishinvasionmechanismZoology118(6)424ndash432httpsdoiorg101016jzool201508003
PerkinsATBoettigerCampPhillipsBL(2016)Afterthegamesareover Life-history trade-offs drive dispersal attenuation followingrangeexpansionEcology and Evolution6(18) 6425ndash6434httpsdoiorg101002ece32314
Perkins A T Phillips B L Baskett M L amp Hastings A (2013)Evolutionofdispersalandlifehistoryinteracttodriveacceleratingspread of an invasive species Ecology Letters 16(8) 1079ndash1087httpsdoiorg101111ele12136
Perry W L Jacks A M Fiorenza D Young M Kuhnke R ampJacquemin S J (2013) Effects of water velocity on the size andshapeofrustycrayfishOrconectes rusticus Freshwater Science32(4)1398ndash1409httpsdoiorg10189912-1662
PerryWLampJonesHM (2017)Effectsofelevatedwatervelocityon the invasive rusty crayfish (Orconectes rusticusGirard 1852) inalaboratorymesocosmJournal of Crustacean Biology38(1)13ndash22httpsdoiorg101093jcbiolrux092
Phillips B L (2009) The evolution of growth rates on an expandingrangeedgeBiology Letters5(6)802ndash804httpsdoiorg101098rsbl20090367
Phillips B L (2015) Evolutionary processesmake invasion speed dif-ficult to predictBiological Invasions17(7) 1949ndash1960 httpsdoiorg101007s10530-015-0849-8
PhillipsBLBrownGPampShineR(2010a)Evolutionarilyacceleratedinvasions The rate of dispersal evolves upwards during the rangeadvanceofcanetoadsJournal of Evolutionary Biology23(12)2595ndash2601httpsdoiorg101111j1420-9101201002118x
PrinsR(1968)ComparativeecologyofthecrayfishesOrconectes rusti-cus and Cambarus tenebrosusinDoeRunMeadeCountyKentuckyInternationale Revue der gesamten Hydrobiologie und Hydrographie53(5)667ndash714httpsdoiorg101002(issn)1522-2632
RabyGDGutowskyLFGampFoxMG (2010)Dietcompositionandconsumptionrateinroundgoby(Neogobius melanostomus)initsexpansionphaseintheTrentRiverOntarioEnvironmental Biology of Fishes89(2)143ndash150httpsdoiorg101007s10641-010-9705-y
RebrinaFSkejoJLucićAampHudinaS(2015)Traitvariabilityofthesignalcrayfish(Pacifastacus leniusculus)inarecentlyinvadedregionreflects potential benefits and trade-offs during dispersalAquatic Invasions10(1)41ndash50httpsdoiorg103391ai
Reisinger L S ElginAK TowleKMChanD Jamp LodgeDM(2017)TheinfluenceofevolutionandplasticityonthebehaviorofaninvasivecrayfishBiological Invasions19(3)815ndash830httpsdoiorg101007s10530-016-1346-4
Ronce O amp Clobert J (2012) Dispersal syndromes In J ClobertMBaguetteTGBentonampJMBullock(Eds)Dispersal ecology and evolution(pp119ndash138)OxfordUKOxfordUniversityPresshttpsdoiorg101093acprofoso97801996088980010001
Rosenthal SK StevensSSampLodgeDM (2006)Whole-lakeef-fects of invasive crayfish (Orconectes spp) and the potential for
restorationCanadian Journal of Fisheries and Aquatic Sciences63(6)1276ndash1285httpsdoiorg101139f06-037
SargentLWampLodgeDM(2014)Evolutionofinvasivetraitsinnon-indigenous species Increased survival and faster growth in inva-sivepopulationsofrustycrayfish(Orconectes rusticus) Evolutionary Applications7(8)949ndash961httpsdoiorg101111eva12198
ShineRBrownGPampPhillipsBL(2011)Anevolutionaryprocessthat assembles phenotypes through space rather than throughtime Proceedings of the National Academy of Sciences of the United States of America 108(14) 5708ndash5711 httpsdoiorg101073pnas1018989108
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SUPPORTING INFORMATION
Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle
How to cite this articleMessagerMLOldenJDPhenotypicvariabilityofrustycrayfish(Faxonius rusticus)attheleadingedgeofitsriverineinvasionFreshwater Biol 2019001ndash14 httpsdoiorg101111fwb13295
