Studies on comparative ecology and ethology in adult populations of several species of Morpho...

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Studies on comparativeecology and ethology in adultpopulations of several species ofMorpho butterflies (Lepidoptera:Morphidae)Allen M. Young aa Department of Biology, Lawrence University,Appleton, Wisconsin, 54911, U.S.A.Published online: 19 Nov 2008.

To cite this article: Allen M. Young (1973) Studies on comparative ecology and ethologyin adult populations of several species of Morpho butterflies (Lepidoptera: Morphidae),Studies on Neotropical Fauna, 8:1, 17-50, DOI: 10.1080/01650527309360452

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Studies on the Neotropical Fauna 8 (1973), pp. 17-50.

Studies on Comparative Ecology and Ethologyin Adult Populations of Several Species of

Morpho Butterflies (Lepidoptera: Morphidae)

by

ALLEN M. YOUNG(Appleton)

The analysis of spacing patterns in populations of mobile animals, recently reviewedby Brown and Orians (1970), is a problem in both ecology and ethology (Crook1970). The ethological aspect of the problem primarily concerns the mechanismand type of social interactions among members of a breeding population; theecological aspect is concerned with relating social interactions to the physicalenvironment and biological community in which the species lives. Both aspects,however, enjoy a common basis in that they both emphasize the joint speration ofspacing (dispersion) pattern and courtship strategy in the determination of thebreeding structure of a population. Spatial dispersion, be it an adaptation toreproduction, predation pressure, or competition (Brown & Orians 1970), involvesa higher individual survival and enhanced reproductive success for those members ofthe population with optimal sites in the habitat. And in studying the spacingpatterns in populations of selected species, it is important to recognize that suchadaptations are molded in evolutionary time by two different sets of selectionpressures: (1) phylogenetic properties of the group in question, and (2) selectiveforces arising from ecological interactions within the population and community.Spacing pattern has been emphasized with respect to how it permits a speciespopulation to fit into a given community structure (Wynne-Edwards 1962, Pielou1969).

This paper is concerned with the comparative spacing patterns and courtshipstrategies in three species of Morpho butterflies (Lepidoptera: Morphidae), as seenin natural populations in Central America. Spacing pattern is used here to describethe distribution of the population's adult membership over the suitable habitat,while courtship strategy refers to the movements and stimuli of individuals of bothsexes that result in encounters leading to copulation and successful fertilization.Thus, spacing pattern refers to the spatial distribution of a population's member-ship, and for mobile species, it is primarily the result of adaptive activities affectingfitness, namely, foraging, feeding, defense, and reproduction.

Most studies of spacing patterns and courtship strategies have been done invertebrate populations, most notably birds (Wynne-Edwards 1962; Lack 1970;Brown & Orians 1970). The apparent high diversity of tropical butterflies in theNew World tropics suggests different evolutionary origins of spacing patterns andcourtship in these insects. Morpho butterflies are among the largest and most

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conspicuous flying insects in the Central American humid tropics and thus, likebirds, render themselves as very useful subjects for the study of insect behaviorpatterns outside the laboratory. In this paper, species-specific differences in spacingpatterns and courtship strategies in natural populations are emphasized in relationto other aspects of the ecology of Morpho (Young 1971a,b,c; Young 1972a,b;Young & Muyshondt 1972a,b,c).

NOTES ON THE SPECIES STUDIED

The three species forming the basis of this study are Morpho peleides limpidaKollar, M. amathonte centralis Deyrolle, andM theseus aquarius Godman. While allthree butterflies are about the same size, they belong to different phylogeneticgroups within the genus (Seitz 1924) and thus, to some extent, possess differentevolutionary histories. These morphological differences are also emphasized interms of life histories and natural histories of these species (Young & Muyshondt1972a,b,c). The occurrence of strong sexual dimorphism in M. amathonte andreduction (M. peleides) or virtual lack of it (M. theseus) (Figure 1) is indicative ofdifferences in courtship strategy between these species.

General coloration of the dorsal wing surfaces is very different among thesespecies of Morpho. While M. peleides and M. amathonte are both basically irrides-cent blue, the latter species is far more brighter and with an essentially mirror-likereflectance (Young 1971b). M. theseus is even more different from the others beingdull whitish-brown and lacking reflective properties or irridescence altogether. Thatsuch morphological differences in the wings of Morpho are perhaps related todifferences in adult behavior involving flight movements is suggested by studies onthe role of large conspicuous color patches on wings as stimuli for courtship invarious Satyridae (Tinbergen et al. 1942), a group of generally dull brown butter-flies phylogenetically very close to the Morphidae (Ehrlich 1961; Ehrlich & Raven1965). At rest, all three species are very inconspicuous due to the cryptic colorationof the ventral wing surfaces.

It is noteworthy to also emphasize that there occur great differences amongthese species in terms of extent of geographical variation and breadth of habitatselection within and along altitudinal gradients in Central America, differenceswhich influence the likelihood of more than one species occurring in the samehabitat at the same time. Of the six species of Morpho known for Central America(M. cypris, M. granadensis, and M. polyphemus have not been studied), these threespecies offer the greatest differences in geographical distribution and habitat selec-tion. First, M. amathonte in generally confined to lowland and premontane pri-mary-growth moist forests, while M. theseus in confined to montane and cloudforests, typically at elevations greater than 700 meters. Both of these species showvery patchy distributions in primary growth forest habitats and while perhaps verylocally abundant, other extensive areas of apparently suitable habitat reveal veryfew or no individuals on a yearly basis. M. peleides, on the other hand, is the mostwidespread and abundant of the three species, occurring as rather large (Young, in

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Fig. 1. From left to right (females above, males below): Morpho amathonte centralis, Morpho peleides limpida, and Morpho theseusaquarius. AH individuals shown about 1/2 natural size.

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prep.) populations in both lowland, premontane, and montane forests, where itoccurs primarily in disturbed second-growth habitats along roads, mud slides, andrivers. At least 30 subspecies or varieties are known in Central America from M.peleides, while markedly less geographical variation occurs inM amathonte andMtheseus (Seitz 1924). This pattern is consistent with the observations of M. peleidesas a widespread second growth species andM. amathonte andM theseus being rareand patchily-distributed (but locally abundant where a patch occurs) butterflies.While larval food plant specificity inM. peleides is broad locally (Young & Muyshondt1972a), it is predicted to be very narrow forM amathonte andM theseus (Young& Muyshondt 1972c, Young 1972a). Similarly, the likelihood of strict unpalatabi-lity is greatest in primary-growth forests species likeM amathonte andM theseus.Recently (Young 1972a), it has been advanced that a second growth species like M.peleides, with broad local range of larval food plants, is a prime candidate forautomimicry (Brower 1970) in which a local population contains both palatableand unpalatable individuals in a numerical abundance determined to a large degreeby relative availability of food plants and the relative rates of exploitation (oviposi-tion strategy) on these plants. Thus, there is a tendency for strict unpalatability tobreak down locally in populations of M peleides. This is a result of M. peleidesbeing a species of less stable communities (Margalef 1968), possession of a broadlarval feeding preference, and the well known variability of secondary compoundsand other feeding stimulants among even related plant species (Levin 1971).

In addition to a broad local larval food plant specificity and larger adultpopulation size in M peleides, other behavioral aspects of life history in secondgrowth communities include single oviposition and non-gregarious larvae (Young &Muyshondt 1972a). On the other hand, primary-growth forest species like M.amathonte and M. theseus are predicted to possess more specialized behavioralpatterns in the forms of cluster oviposition and highly gregarious larvae on the foodplant (Young & Muyshondt 1972b). Such specializations result from the evolutionof narrow larval food plant specificity coupled with the usual highly patchy spatialdistribution of many woody plant species in primary growth tropical forests (Pires,Dobzhansky, & Black 1953). Such a community structure allows for a concentra-tion of reproductive effort (Labine 1968; Young 1972c) per adult female over afew single patches of a food plant, facilitated by selection for egg-clustering.

All of the above factors concerning these three species of Morpho have bearingon the types of spacing patterns and courtship strategies evolved by these butter-flies and any logical interpretation of the adaptive significance of these behavioralpatterns must account for these ecological properties in natural populations. Forthis reason, these properties will be discussed later with respect to the observedbehavioral patterns. In fact, information from other species of Morpho will also beused in this context.

The above sorts of information on the ecology and ethology of Morpho areuseful for the analysis of adaptive strategies of dispersal and courtship in popula-tions. But this paper goes even further, by providing further information on variousecological and ethological parameters underlying dispersal and courtship strategiesin Morpho. And since the three selected Central American species have different

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ECOLOGY AND ETHOLOGY OF ADULT MORPHO 21

phyletic origins (M. amathonte is in the rhetenor group, M. peleides in the achillesgroup, and M. theseus in the laertes group - Seitz 1924), it may be expected thatthese species have diverged considerably with respect to ecological and ethologicaladaptations.

GENERAL METHODS

All field studies were conducted at three different localities in Costa Rica, (Figures2-4) intermittently from January 1970 to September 1972. M. amathonte wasstudied at Finca la Selva, near Puerto Viejo in the Caribbean lowlands (89-100melev.); the habitat (Figure 2) is relatively undisturbed primary-growth premontanetropical wet forest (Holdridge et al. 1971). BothM. peleides and M. theseus werestudied at Cuesta Angel, near Cariblanco in the Heredia Province; the habitat isprimary and secondary-growth montane (900-1000 m elev.) wet forest (Figure 4).At this locality, both species of Morpho prevail, being sympatric, although occa-sionally M. amathonte also occurs there (the first record of this species was takenon June 28, 1972 when a single fresh male was seen flying up the Rio Sarapiqui).M. peleides was also studied at Bajo la Hondura (900-1000 m elev.), anothermontane forest site (San Jose Province) but on the Pacific slopes of the CentralCordillera (Figure 3). M. peleides is unusually abundant at both Cuesta Angel andBajo la Hondura. At Fince la Selva and other localities in the Caribbean lowlands,M. amathonte occurs with M. peleides, M. cypris, and M. granadensis. Only M.peleides is found at Bajo la Hondura, and only M. theseus regularly occurs with it atCuesta Angel.

M. amathonte was studied from January through June 1970 at Finca la Selva,while M. peleides was studied at Cuesta Angel and Bajo la Hondura from mid-Junethrough early September 1971. M. theseus was studied at Cuesta Angel concurrentlywith M. peleides. There was a total of 109 days of field observation (to be outlinedbelow) on M. amathonte, 57 days for M. peleides (for both localities), and 29 daysforM theseus.

Essentially four major kinds of field studies were conducted on each species ofMorpho during their respective study periods: (1) "capture-mark-release" experi-ments employing both natural food sources and experimentally-placed fermentingfruit baits (Figure 5), as an approach to estimating population cohesiveness,population size, and adult population age-structure; (2) observations on diurnalactivity patterns associated with feeding, courship, and oviposition; (3) observationson adult habitat preferences (habitat selection) with respect to feeding, courtship,and oviposition; (4) observations on courtship encounters and aggressiveness atfeeding sites and in general habitat.

The 1970 experiment of capture-mark-release \nM. amathonte was conductedessentially at a single natural food source of the butterfly. This experiment, part ofa larger study, is described in depth elsewhere (Young 1972b), and it consisted ofcapturing, marking, and releasing all adults seen feeding at accumulations of rottingfruit of a canopy tree species, Coumarouna oleifera (Leguminosaej. Four different

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Fig. 2. San Miguel de Sarapiqui, Heredia Province, Costa Rica. This region, premontane tropical wet forest, is the major habitat ofMorpho amathonte. Breeding populations remain confined to primary-growth forest seen off in the distance. Elevation is about150 m.

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Fig. 3. Bajo la Hondura, San Jose Province, Costa Rica. Morpho peleides is very abundant here. This montane forest region (about 1000m elevation) is on the Pacific slopes of the central Cordillera; M. peleides is the only Morpho found there.

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Fig. 4. Cuesta Angel de Sarapiqui, Heredia Province, Costa Rica. Both Morpho peleides and M. theseus are abundant here Thismontane forest region (1000 m elevation) is on the Caribbean drainage of the central Cordillera. M peleides is most abundantalong second-growth associated with roadcuts, landslides, and river edges, while M. theseus is found primarly in undisturbedforest.

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Fig. 5. Morpho butterflies on natural and experimental food sources, Cuesta Angel, July-August 1971. (A) unmarked M. peleides (9) on banana bait, (B) unmarked M. theseus(t5) on mango bait, (C) marked M. peleides (9) on banana bait, and (D) marked M.peleides (o) feeding on fermenting fungi at tree wound.

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highly dispersed individual trees dropping fruit were selected for study, withmarking occurring during the January-June study period. The marking techniqueused for all three species of Morpho was the applying of a small code numberon the ventral surface of each hindwing near the ocelli; the paint used was"Flo-Paque", a fast-drying enamel base preparation. Since the butterflies feedinvariably with their wings closed, it is possible to resight previously-markedindividuals with relative ease, needing only a pair of binoculars. Each individualcaptured for marking was recorded with respect to date of capture, sex and wingcondition; the extent of wing fading, loss of scales, and tattering are useful criteriain determining the approximate age of an individual adult Morpho. And, bymarking very young ("fresh", "teneral") adults, it is possible to obtain a consistentpattern of changes in physical appearance indicative of age. Eventually, a crude lifetable may be constructed in this manner.

The 1971 experiments with M. peleides and M. theseus at Cuesta Angeland Bajo la Hondura consisted of experimentally placing clumps of fermen-ting fruit baits along a transect in forest understory, usually near a clearing. At Bajola Hondura, the exact same experiments were repeated each year and in the sameplace. The transect at Cuesta Angel was about 50 meters long and a total of 12clumps of fermenting bait were distributed at 4 meter intervals along it. Thetransect was in an open area overlooking a cliff (8 meters high) bordering the RioSarapiqui. All around this clearing is primary-growth forest. Equal-sized (about 18inches in diameter) clumps of fruit bait (which had been fermenting in a smallamount of rum for 3-5 days) were placed on dishes of aluminum foil on the groundand allowed to stand for at least one day before beginning observations. Fruits usedin both years were banana and mango, strong attractants of Morpho and otherforest butterflies (Young 1972d). Each experiment lasted 5-7 days and five suchexperiments were conducted at both localities during 1971. Variability inthe duration of an experiment was due primarily to rainfall, since heavy rainswashed out the baits and reduced their effectiveness in attracting Morpho.In fact, several other experiments of this sort had to be discarded due toinclement weather. Baits were visited at all hours of the day for estimationof diurnal foraging activity patterns. M. peleides was discovered in July 1971to feed on small patches of fermenting fungi growing of the trunks of fallenCordia trees that had been recently cut down. This site is about 50 meters fromwhere the bait transect was located, and adults were also observed (and marked) atthis natural food source. Natural fruit food sources of M. peleides and M. theseushave not been found. At Bajo la Hondura, a transect of similar length and baitdistribution was established in a young second-growth clearing on the Rio Claro.Three experiments were conducted in 1971. Again, the sides of the valleyare covered with primary-growth forest and some very old second growth. Nonatural fruit food sources of M. peleides have been found to date at this locality.

At both localities, the transects were set up at places where many individuals ofM. peleides were seen. This probably introduced a bias in terms of sampling M.theseus at Cuesta Angel, since this species was sampled on the same transect asMpeleides. A lack of time prevented the setting up of additional transects further into

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the forest interior to sample M. theseus. However, the data obtained on theabundance of M. theseus is probably accurate since other field observations on thespecies has revealed similar numbers of adults.

The marking experiments at Cuesta Angel were: June 25-30, July 5-12, July20-26, August 4-10, and August 23-September 1 (1971). At Bajo la Hondura, thedates were: July 1-4, July 14-19 and August 12-18 (1971).

Observations on marked and unmarked adults at fruit baits and natural foodsources (Figure 5) over several hours daily gave data on diurnal patterns of foragingin the three species of Morpho. On other days, butterfly activity was observed inthe general habitats, for data on any diurnal patterns associated with courtship andoviposition. For M. amathonte there were a total of 28 days of such observationaway from food sources, 34 days for M, peleides, and 36 days for M. theseus. Tostudy adult activity on a given day, the habitat was walked for several hours,covering selected places where adults were known to be abundant. These placesincluded river edges, paths through forest, roadsides, and exposed strips of bareearth down the sides of ravines, formed by large mud slides. The same places werevisited on different days, so that replicate records of adult activity could beobtained from the same places, minimizing effects of environmental variability overdifferent places (if such effects exist).

The same procedure was used to study habitat preferences by adult Morpho ateach locality. But more places were visited in order to determine if the species inquestion was primarily second-growth or primary-growth in habitat preference.Observations were also made of the occurrence of adults above primary-growthforest canopy. This was done by selecting high points along ridges associated withthe ravine (Cuesta Angel and Bajo la Hondura) and looking down over the canopywith binoculars. Since the butterflies are large and often conspicuous, it is easy todetect their presence, over moderately long distances, by this technique. Canopysampling for M. amathonte at La Selva was more difficult, with observations beingmade from clearings in the forest where the exposed edge of the canopy could beseen.

The frequency of courtship encounters was studied at food sources and at otherplaces in the general habitat at each locality. The observation procedures outlinedabove made it possible to witness any male-female interactions (chases, attemptedcopulations, and copulations) at food sources and in general habitat. The techniquewas very reliable and easy for the dimorphic species, but difficult for M. theseus.This initial difficulty was overcome by eventually becoming familiar with the sizedifference between the two sexes in this butterfly, and by recognizing the slightlylighter underside coloration of the wings in the female. Courtship encounter is usedhere to mean any form of male-female interaction in the field. Aggressive interac-tions among males or females were also studied at food sources and in the generalhabitat. In addition, inter-male aggressiveness in M. peleides was studied in thelaboratory.

A wire mesh cage (with wooden framing), 10 feet long by 5 feet wide and 6 feetwide, was set up on a shaded patio in San Jose, Costa Rica, and outfitted with aplate of fermenting banana bait and a few potted plants for shade. Each experiment

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consisted of placing 10 healthy young males (4-7 days after eclosion) of M. peleidesinto the cage at one time (these individuals being recently caught) and observingtheir interactions on a daily basis. An experiment of this sort usually lasted oneweek.

The major reason for selecting 10 individuals is that males show signs of"agitation" when this quantity is placed in a slightly smaller cage. Furthermore, theapproximate diameter of the food source is held at 8 inches since it is notuncommon to find several adults feeding within a smaller area of bait in the wild.Water was sprinkled on the cement floor of the cage once daily and this resulted inthe formations of small concentrations of water ("watering holes") where the floorwas uneven. Aggressive displacement of feeding and drinking males was thenstudied for several hours each day. Since each male was individually marked with anumber code, it was possible to determine individual aggressiveness within anygroup of six males. Different males were always used in separate experiments. Atotal of five experiments were conducted during July and August 1972. The designof the experiments also permitted the determination of those individual maleswhich probably died as a result of being prevented from feeding or drinking severaldays.

The basic rationale underlying this experiment is that if aggression exists itshould prevent certain individuals (phenotypes) from feeding due to aggressivedisplacement among males. Thus certain individuals would be expected to feed fora significantly shorter time than other (more aggressive) individuals. All individualsfeeding for approximately the same amount of time indicates lack of aggressivebehavior. All individuals used are starved two days before the experiment is begun.

Finally, a small experiment was conducted to examine, in a preliminary way, theregularity of flight movement in M. theseus and M. peleides. This experiment wasperformed on two days, August 15 and August 17,1972, at Cuesta Angel. Each dayconstituted a replicate and the exact same procedures were followed on both days.On each day, an observer was positioned on the edge of a steep (75-80° incline)river (Rio Sarapiqui) gorge about 250 feet high. The location of this observer wasalong a section of the gorge where both M. theseus and M. peleides are unusuallyabundant on sunny mornings. Adults of both species frequently fly up the oppositeside of this gorge, exactly across from where the observer is positioned. Adult flightactivity to either side of this section of gorge is absent. This is explained in part bythe fact that this section of gorge is covered with low, young second-growthvegetation, while to either side of this 75-meter strip, there is nothing but primary-growth forest. Thus the butterflies have an open area to fly up the gorge and overthe ridge. The object of study was to observe the pattern of individual butterflymovement up the side of the gorge, and within the general air space within thegorge. The precise position of the observer on the opposite side of the gorgefacilitated the immediate sighting of a Morpho flying from virtually all directionswithin and above the opposite face of the gorge. On the two days of observation,the observer scored (1) the number ofM. theseus andM. peleides flying through thearea, (2) the direction and trajectory of flight of each individual, and (3) the time(hour) of individual sightings. All observations were made between 9:00 A.M. and

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12:00 noon (C.S.T.) each day, since the activity of adult Morpho is greatest duringthese sunniest hours of the day at Cuesta Angel. No adults were caught and marked,as the sole purpose of this pilot study was to determine the regularity of flightmovement in a comparative manner for these two species in the gorge. Theregularity of movement by each individual, which is only apparent through mar-king-resighting analyses, will be studied in depth later. The regularity of individualflight movement for M. amathonte has already been studied (Young, 1972b), inwhich it was found that individual males retain the same flight routes throughforest habitat over several successive months. Each male possesses a circular flightroute which originates and ends at a food source and each flight movement alongthe route covers several hundred meters of habitat. This pattern of movement isvery regular, and is referred to as "long distance circular movement". Flightmovements of females of M. amathonte are probably more erratic and non-regular(Young, 1972b).

RESULTS

Observations and experiments are summarized here under these major headings: (1)Cohesiveness of Adult Populations, (2) Habitat Selection, (3) Diurnal ActivityPatterns, and (4) Notes on Courtship Strategies.

Cohesiveness of Adult PopulationsTable 1 summarizes the marking-resighting data obtained for M. amathonte in aprevious study (Young, 1972b). The most striking result of this marking program isthe very high proportion of marked male resightings at Coumarouna fruits over asix-month period in lowland primary-growth forest (Table 1). Of interest also is thelow number of resightings of marked females, and the disproportionately highnumber of males assuming a sex ratio of unity (Table 1). The high proportion ofmales and resightings of the same individuals is explained by the additionalobservation of males establishing very regular circular flight routes which centeraround a Coumarouna tree dropping fruit (Young, 1972b). These flight routes areindividual-specific and are traveled several times each day during the morning. Atpoints of overlap between the flight routes of two or more males, aggressive assaultsfrequently occur, resulting in a temporary scattering of all individuals involved.Since Coumarouna trees in lowland forest are generally hyperdispersed and thecircular flight paths of individual male M. amathonte very large, the spacing patternof the adult male population is fairly uniform, with very low male density.Courtship encounters occur almost exclusively along the flight routes of individualmales and thus this spacing pattern determines in part the breeding strategy of thespecies. The male flight strategy is thus one of "long distance circular movement"in which the individual circular flight routes function to disperse the competentmale population and to facilitate courtship encounter with females. Courtship doesnot occur at feeding sites; this activity is restricted to the long distance flightroutes.

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Table 1. Frequency of daily resightings of previously marked adult Morpho ama-thonte butterflies at Finca la Selva, Heredia Province, Costa Rica*.

Date

Jan. 14,1970151618

Feb. 5678

Mar. 1011121518

Apr. 6789

May 172022

Duration ofobs. period

5.45.05.45.25.05.05.15.45.45.25.25.45.05.05.45.45.25.25.45.2

No. previouslymarked by

this date (hrs.)

2022232324242424242424242424252525252525

Proportions ofButterflies resighted

66

0.950.901.001.00.90

1.00.95.95.90

1.00.92.95.90

1.00.90.90

1.00.86.90.95

99

0.000.000.000.000.000.100.000.050.000.000.050.000.000.100.000.000.050.000.000.00

* Given are proportions seen over four feedings sites; all observations each day within theinternal 7:00-12:24 A.M. Extracted from Young (1972b).

But males exhibit pronounced aggressive behavior at feeding sites. When one ormore males are feeding and another one flies into the feeding site and very close toone of these individuals, invariably the feeding is interrupted and the males fly upand charge at the "intruder". Such behavior often results in several males beingaroused to temporary short-distance flight movement about the Coumarouna tree.Eventually all individuals settle down at feeding. Such interruptions characterizemale M. amathonte behavior at feeding sites and they generally result in awide scattering of feeding individuals over the entire drown shadow produced by thefruit fall. Unlike in M. peleides below, one never encounters male M. amathontefeeding very close (within a few cm) to one another; individuals are always veryscattered under the tree.

Adult male population cohesiveness is very high in M. amathonte since there isvirtually no exchange of males among different feeding sites, nor do males abandontheir flight routes during the entire fruiting season of Coumarouna. Whether or not

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a similar spacing pattern is established around other food sources at other times ofthe year remains to be determined. As the Coumarouna fruit-drop fades away, thisspacing pattern is altered (Young, 1972b). Thus while there is very high adult malepopulation cohesiveness, there is also an even dispersion of competent males overthe habitat. Cohesiveness is achieved through the establishment of essentially"point-centered" flight routes around a suitable food source and territorial defenseof flight routes, which cover large areas of habitat. Coverage of a large area byindividual males on a day-to-day basis over several months time facilitates thelocation of unmated females for courtship. The necessity for such flight movementis demonstrated by the highly secretive behavior of females. From low resightings atCoumarouna fruits and the general difficulty in finding females, it is apparent thatfemales either do not prefer this food source or else have very erratic flightmovement. Female flight movement is very irregular while male movement is veryregular. It is the male component of the population which is responsible for thecohesiveness and general spacing pattern that facilitates courtship.

The regularity of individual flight movement is very different in both sexes of M.peleides (Table 2), compared to that of M. amathonte. Here, there is generally lowand erratic returns of marked individuals of both sexes to fruit baits (Table 2).Another fact not revealed by Table 2 is that marked individuals tend to returnrepeatedly to the fruit baits over a two-month period, but at very erratic intervals.Of course, a good proportion of individuals do not return after the date of marking(Table 2). In general, there is less adult population cohesiveness in M. peleides thanin M. amathonte. The pattern is the same for this species at a natural food source,fermenting fungal growths on decaying tree trunks (Table 3). Perhaps even moreinteresting in a comparative manner is the higher numerical abundance of female M.peleides at fruit baits, than seen for female M. amathonte at Coumarouna fruits,and the very similar male-female proportions of resightings in the former species.While females have a slightly suppressed proportion of resightings over males, whichis probably due to more extensive movement in search of suitable oviposition sites,their numbers at baite almost equal those of the males (Table 2). This observation isexplained by two factors: (1) both sexes have similar feeding preferences, and (2)feeding sites are major sites for the courtship of recently-eclosed unmated females.Both sexes are often found feeding side by side on an individual bait and matedfemales are not persued by males. Very young unmated females usually arrive atbaits by late morning (after 11:00 A.M.) by which time mated females and manymales have already finished feeding. The courtship of unmated females generallytakes place between 11:00 A.M. and 4:30 P.M., depending on the time of commen-cement of afternoon rainstorms at Cuesta Angel and Bajo la Hondura. Thus unlikeM. amathonte, feeding sites are major courtship sites in M. peleides. Feeding sitesare probably the only places in the habitat where both sexes are likely to meet onany regular basis. The erratic resightings of marked individuals underscores thehighly mobile capacity of populations of this species. As to be summarized furtherbelow, flight movements of both sexes are highly erratic and marked individuals areseldom seen along the same open clearings on a day-to-day basis. Males lack theregularity of flight seen in male M. amathonte, and aggressive encounters in the

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Table 2. Frequency of daily resightings of previously marked adult Morpho peleidesbutterflies at Cuesta Angel de Sarapiqui, Heredia Province, Costa Rica.*

Date

Juli 3, 197145

161920

Aug 91013172023


5.55.05.05.25.25.05.45.05.05.25.05.0

No. previouslymarked by

this date (hrs.)

38475056596372798395

108118


66

0.200.150.120.220.300.160.070.100.120.200.150.12

99

0.100.080.100.160.120.200.180.200.200.160.200.20

* Given are the daily total numbers seen at fermenting fruit baits experimentally placed in atransect fashion in one region of forest understory. The data were strikingly similar for thesame experiment conducted at Bajo la Hondura.

field are of very diminished intensity. The laboratory studies on aggressive displace-ment of marked male M. peleides when a single reduced amount of food is in thecage revealed that all individuals can feed together without certain males beingdeprived of feeding. Repeated experiments with different males gave the sameresults. Since courtship takes place at feeding sites in the wild it therefore seemsthat aggressive behavior is not a component of courtship, unlike the situation inM.amathonte where courtship entails aggressive behavior among males of different flightroutes at points of overlap. In the laboratory studies with male M. peleides, thenecessity for 10 individuals to feed more or less simultaneously (range of 6-10individuals feeding at any one time) during one experiment results in agitationamong the butterflies, but every male is able to feed for approximately the sameamount of time. Agitation is manifested by the combined motion of wing flappingand walking on the bait. Occasionally agitation results in one or more individualsleaving the food, but these invariably return within a few minutes to resumefeeding. In the wild, as many as 7 males have been seen feeding together within avery small area (8-13 cm diameter) on fruit bait (Young & Muyshondt, 1972a). Ittherefore appears that males of M. peleides are not as aggressive as males of M.amathonte on their flight routes.

M. peleides adults are most frequently found flying through open areas such asroadcuts, rivers, ravines, and forest edges. The species generally avoids the dense

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forest but flies along paths and trails. Thus, unlike M. amathonte, the spacingpattern of adults in M. peleides is determined in part by local topographic factorsand forest structure. The other major factor influencing the spacing pattern isstrong selection for high vagility associated with the colonization of recently-for-med second-growth habitats and other pioneer plant communities (Young & Müys-hondt, 1972a). The result of the operation of these factors is a rather continuousdistribution of highly mobile adults along extensive open habitats. This spacingpattern, the result of dispersal of both sexes, is probably uniform along openhabitats but "patchy" in the sense of avoiding dense forest. Females are moremobile than males, presumably the result of searching for suitable oviposition sitesin second-growth vegetation. At Cuesta Angel, marked females have been observedto fly up the side of a 300-meter high ravine in search for oviposition sites. These

Table 3. Frequency of resightings of previously marked Morpho peleides butterfliesat a natural food source*, Cuesta Angel de Sarapiqui, Heredia Province,Costa Rica and Bajo la Hondura, San Jose Province.

Date

July 7, 197189

102325

Aug. 34567

July 62122

Aug. 24252627


5.05.05.25.04.85.25.05.05.05.25.0

BAJO

5.25.45.25.05.05.25.2

No previouslymarked by

this date (hrs.)

2830262640414143454546

LA HONDURA

181922282930 .30


66

0.060.090.080.120.100.080.200.180.140.200.22

0.080.080.120.100.200.180.20

9?

0.040.060.130.200.150.100.120.100.200.180.14

0.160.100.100.120.100.080.18

* Growths of fermenting fungi in sap wound on a few trees within 4 m of each other, at eachlocality.

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34 A.M. YOUNG

individuals were originally marked in the bottom of the ravine. Of a total of 88females marked here over a two year period, 30 were resighted at the top of theravine and several (4-16) days after marking. Observations were made at the top ofthe ravine along a section of roadcut where several larval food plants are unusuallyabundant and oviposition activity very high in this species. Females predominatealong the roadcut, while males are more abundant lower down in the ravine wherefeeding sites prevail. This spatial separation of mated females from males is theresult of the search for oviposition sites by the former individuals. Teneral andyoung females are abundant lower down in the ravine.

Like male M. amathonte and very unlike M. peleides, both sexes of M. theseusexhibit very high residentiary (Table 4). Individuals of both sexes are equallyabundant and show the same high level of returns at baits. Such observationssuggest the operation of a "group" home range behavior in which many individualswithin a local population tend to remain in the same area of habitat on a regular(daily) basis. While regular return to a food source is seen inM. amathonte, it onlyoccurs in males (Table 1). SoM. theseus exhibits a pattern of flight movement verydifferent from both M. amathonte and M. theseus. This pattern results in a verytight adult population cohesiveness in which the population's membership enjoy acommon home range over a rather limited area of the habitat. This idea issubstantiated below when the flight movements of M theseus are contrasted withthose of M. peleides. The amount of habitat covered by individual movement in M.theseus is probably considerably less than that covered by either sex of M.amathonte. While male M. amathonte are circular long distance fliers, both maleand female M. theseus are circular short distance fliers. The latter situation resultsin a patchy distribution of M. theseus populations with patchiness resulting fromthe high cohesiveness within any one population and the short distance flight habitsof both sexes.

On August 15, 1972, a total of 27 M. theseus passings were recorded in the rivergorge study; since marking was not done, the number of individuals involvedremains undetermined. All 27 passings occurred within the period 9:15 to 11:08A.M. Heavy overcast after this time resulted in a cessation of flight activity. OnAugust 17, a total of 35 passings were noted from 8:59 to 10:35 A.M. The samegeneral flight patterns were very evident on both days: more than 70% of theindividuals flew up the opposite side of the ravine; of these, between 55% (August15) and 65% (August 17) came initially from the same direction (downstream) andthen flew up the side of the gorge. The amount of time between the passage of twosuccessive individuals varied between 1.5 and 10 minutes (mean value of 2.7 min.).Occasionally two individuals followed each other very closely. The remaining 30%either continued to fly through the gorge, without detour, or else reversed directionand flew in the opposite direction (downstream or upstream). Of all the passings upthe opposite side of the gorge, the trajectory of flight was always the same:movement was about 40° with the river bottom as a horizontal reference point sothe slope was never climbed vertically (i.e., 90° with the river bottom). Abouthalfway up the slope, flight was reversed (and almost horizontal) and then followedby a second reversal and a final reversal just below the top of the gorge. Each

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Table 4. Frequency of daily resightings of previously marked adult Morpho theseusbutterflies at Cuesta Angel de Sarapiqui, Heredia Province, Costa Rica.*

Date

July 3, 197145

161920

Aug. 91013172023


5.55.05.05.25.25.05.45.05.05.25.05.0

No previouslymarked by

this date (hrs.)

202021242425292930303031


66

0.850.800.850.901.00

.95

.901.00.86.90

1.001.00

99

0.900.900.850.851.000.90

.90

.851.00.90.90.90

* Same experimental baits and habitat as for M. peleides (Table 2, footnote).

individual invariably passed by the same "landmarks" singled out by the observer asuseful reference points for plotting flight trajectories. At the top of the gorge,individuals always flew in the same direction and horizontal with the river bottom;they eventually disappeared behind primary-growth forest and could not be fol-lowed any further. This trajectory pattern was remarkably consistent on both daysand it is interpreted here as being indicative of the occurrence of regular flightmovement inM. theseus. Both males and females partake in it.

A very different picture emerges when observing M. peleides in the samesituation. A total of 63 passings of M. peleides were counted on August 15 (withinthe same time period) and 59 on the 17th. The trajectories of no two passings werethe same and flight was always very erratic. Flight movement up the ravine veryseldom brought two or more individuals to the same point on top of the gorge. Infact, more than 50% of the passings which detoured to the side of the gorge failedto make it all the way to the top. It was virtually impossible for the observer todetect any single consistent pattern of flight movement up the side of the gorge.Many individuals clearly flew up the gorge, but the trajectory was always different.Flight movement is clearly very erratic over short distances inM peleides, especial-ly when contrasted with M. theseus under the same conditions.

Our tentative conclusion regarding the apparent regularity of movement in M.theseus is that several individuals, perhaps a kin group, follow a circular group homerange which covers a relatively small area of habitat. While the precise functions ofsuch a behavior pattern remain undetermined, foraging, courtship, and oviposition

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36 A.M. YOUNG

may be involved. A great deal of adult daily activity is concentrated in severalindividuals over a small common area of habitat which is seldom abandoned.Courtship strategy must involve short range mate searching movements and is thusdifferent from that of M. amathonte where long range circular movement of malesis the major determinant of courtship strategy. The strategy is closer to that of M.peleides where encounters occur at very localized meeting places, feeding sites. ButM. theseus is clearly not as vagile as M. peleides (Tables 2,4) so virtually all matingand egg-laying is localized in the former species while dispersed in the latter.

Habitat Selection

Previous study (Young 1972b) has shown that M. amathonte is primarily a speciesof primary-growth undisturbed forest. Several related Brazilian species of therhetenor group are also forest species (L. R. Otero, pers. comms.).M. amathonte isstrictly a Morpho of primary-growth forest in the sense that the bulk of adultactivity occurs in that habitat. Oviposition is very likely limited to the forestcanopy and at medium heights associated with solid forest clearings such as swampsand places of extensive adult tree fall.

Like M. amathonte in the lowlands, M. theseus is primarily a forest species in themountains. But the habitat of this Morpho extends to the old second-growthassociated with the crests and ridges of ravines. Here the butterfly seldom wandersfar from primary-growth forest and the bulk of breeding activity probably takesplace in the forest proper. Oviposition is apparently restricted to medium and tallheights, as observed in the cruising habits of females searching for suitable foodplants. M. theseus shares a distinct preference for high-altitude forests with severalSouth American species of the laertes group (Seitz, 1924). Virtually all activities inM. theseus are restricted mainly to primary-growth forest. Adults of either sexcannot be found at fruit baits placed on ridge tops in second-growth, but invariablycome to the baits in primary-growth forest. In both cases, baits are placed atstrategic points where adult activity has been substantial.

While M. peleides may occasionally breed in primary-growth forest, it is veryclearly a Morpho of second-growth forest (Young & Muyshondt, 1972a). Manyspecies of legumes are exploited locally as larval food plants in second-growth plantcommunities in various stages of succession. Of the Central American Morpho, itclearly represents a major shift in habitat prefence, having successfully made theevolutionary transition to a species of less stable communites. Adults are easy tobait in second-growth as well as in primary-growth forest which borders on rivers;the reverse is true in solid forest.

Diurnal Activity Patterns

The data already presented in this paper indicate that M. amathonte and M. theseusare specialized species of forests while M. peleides is a generalized species ofsecond-growth vegetation. It is therefore of interest to also consider the extent ofspecialization with respect to partitioning the environment on a daily basis.

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Both M. amathonte and M. theseus exhibit rigid partitioning of the day intodifferent adult activities. More is known about the pattern in M. amathonte(Young, 1972b). Males feed usually between 7:30 and 9:30 A.M. and feeding isfollowed by movement along flight routes for another 2 or 3 hours. Feeding isminimal or absent during this time. By early afternoon, males roost loosely in openareas near their feeding sites (Young, 1971a) and in the absence of courtshipencounter, remain quiet until the next morning. Females always feed later thanmales, usually between 10:30 and 12:00 noon. Courtship and copulation, whichoccur along flight routes, lasts throughout the afternoon and early evening. Oviposi-tion activity presumably begins the following morning since oviposition behaviorhas been observed between 8:00 and 10:00A.M. Adult activity is generally low inthe afternoon hours, although oviposition may continue until 4:00 P.M. Males arevirtually inactive in the afternoon. Copulation has not yet been observed in thisMorpho. Since the bulk of male and female flight activity precedes feeding in thisspecies, it is likely that courtship and copulation are initiated before feeding.

The daily sequence of adult activities is less definitive in M. peleides. Individualsof both sexes do not have a solid block of time devoted to flight activity, as seen inother two species. Rather, flight is intermittent with feeding and oviposition. Andsince in this Morpho courtship encounters take place at feeding sites, it stands toreason that a single period of continual flight activity, so important for courtship inM. amathonte and M. theseus, would be disadvantageous. Generally both sexes canbe found at fruit baits or fermenting fungi at any hour from about 9:00 A.M. to4:00 P.M. Occasionally males are found feeding as early as 7:45 A.M. Flight activityis greatest in the morning and drops off rapidly after about 2:00 P.M. Ovipositionis well documented in this species (Young & Muyshondt, 1972a) and it generallytakes place throughout the day, but seldom after 3:00 P.M. Courtship and copula-tion also occur throughout the day but courtship is greatest during the late morninghours, after many individuals are "recruited" to feeding sites. It is interesting topoint out that a closely related species, M. granadensis, in lowland primary-growthforest has a narrow feeding period concentrated in the very late afternoon hours(4:00-6:00 P.M.) (Young, 1971b). Apparently the generalist strategy ofM peleidesin second-growht habitats is replaced by specialized strategies in undisturbedforests.

The adult activity patterns discussed here for all three species are very vulnerableto local daily weather conditions and only apply on days of maximal sunshine.Undoubtedly the ensuing cloud cover over tropical forests during the afternoonaccounts for the decline of adult activity at about this time. Rainfall and lack ofsunshine suppress the activity of adult Morpho at all elevations.

Notes on Courtship Strategies

Courtship strategy concerns the problem of how two individuals of the oppositesex encounter each other in the habitat to effect copulation. The major key tounderstanding the courtship strategies in different species of Morpho resides, to alarge extent, in the elucidation of spacing patterns within populations. An attempt

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has been made at this problem through a consideration of adult populationcohesiveness in three species. Not only is spatial distribution of sexually-competentindividuals important, but the extent of sexual dimorphism in appearance (Fig. 1) isanother major factor. Furthermore, in species like M. amathonte there appears asharp dichotomy in the non-overlap of peak feeding periods between the sexes, afactor of minimal importance in M. theseus and M. peleides.

It is predicted (Young, 1972b) that the courtship strategy of M. amathonteentails the receptive female "waiting" in secrecy along the flight route of a male.The enroaching crypsis of the dorsal wing surfaces of the female attests to anevolutionary compromise between conspicuousness and secrecy in the initial stagesof courtship. After eclosion, a female positions herself along a male's flight route atsome optimal point where she can easily advertise her presence upon the approachof the male. The male is clearly visible at a considerable distance (barring blockageof view by foliage etc.) owing to the very brilliant solid blue dorsal wing coloration,facilitating detection by the waiting female. When the male is within a certaindistance of the resting female, the latter flies up into his patch of flight and thusadvertises her whereabouts to him. The sexual dimorphism in wing colorationprovides the necessary sensory cue to initiate female recognition by the male, andsubsequently courtship. But at close distance, courtship initiation may involveolfactory stimuli as well (e.g., Myers & Brower, 1969). Such detailed analysis awaitsfurther study in the field and laboratory. The regularity of male flight routes fromday-to-day and the rather even dispersion of males around feeding sites facilitatemate location on the part of the females. In addition, the very large area of habitatcovered by each male on his flight route ensures that most of the environment issearched for mates. Another important factor is the probable hyperdispersion offood plants suitable for egg-laying. Since the tree species diversity of lowlandtropical forests is very high (Pires, Dobzhansky, & Black, 1953) it stands to reasonthat females should adopt a pattern of hyperdispersion to locate them. This is verydifferent from the potential situation in montane tropical forests, the major habitatof M. theseus. Species diversity of high altitude tropical forests drops out, and thisis especially true for many legumes, a major plant family exploited as the foodplants of larval Morpho. Thus for a species like M. theseus, it is advantageous toconcentrate the bulk of movement to within a small area where potential foodplants are located; to disperse over very long distances in search of other foodplantswould mean a greater cost in energy than that by remaining within one area. Theresult, as discussed earlier, is a highly patchy distribution of many small breedingpopulations each one of which is centered around an area of habitat rich inpotential larval food plants. While hyperdispersion is a useful strategy for M.amathonte in lowland forests where most food plants are present but hyperdisper-sed, the even scarcer distribution of food plants in montane forests favors lowvagility and patchy distribution inAf. theseus.

The clear lack of sexual dimorphism in wing coloration in M. theseus (Figure 1)suggests that any courtship strategy in this species involved olfactory cues at veryclose distances; visual cues would be minimal for inter-sex recognition on the wing.Very high adult population cohesiveness and small group home range movements

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favor a courtship strategy in which individuals of both sexes take an equally activerole in bringing about courtship and copulation. The pattern of dispersion of malesis not very different from that of females, and there is a high likelihood thatindividuals of both sexes are found together at the same times and places in thehabitat; this is very different from M. amathonte. Both males and females arepatchily-distributed and their patches intermingle most of the time. Thus in M.theseus, the courtship strategy entails the intermingling of both sexes along grouphome ranges, (Table 5), allowing the exposure of receptive females to males at closedistances to enhance discrimination by olfactory stimuli.

The courtship strategy for M. peleides, a species characterized by large mobileadult populations, involved the promotion of male-female encounters at or nearfeeding sites of many individuals. Thus while the general adult population is usuallylarge and dispersed over a large area of habitat, courtship is limited to those placeswhere individuals concentrate, namely, feeding sites. Whithin the general vicinity offeeding sites, the partial sexual dimorphism in wing coloration (both ventral anddorsal) assist in the recognition of an individual of the opposite sex. At greaterdistances, such sexual dimorphism would be essentially useless in courtship. Thusthe feeding site concentrates many individuals within a small area at certain timesof the day, and courtship takes place there. It is very possible that olfaction is alsoinvolved in sex recognition in this Morpho. Since both sexes often feed together,this co-habitation of males and females permits unmated females to advertise theirpresence to males. Once mated, females probably become more vagile in search ofoviposition sites.

In all three species, courtship involved the male chasing the female within a smallarea. Such movement is usually circular and copulation begins close by. Copulationin M. peleides generally lasts from about 8 hours to 3 days; copulation has not beenobserved inM. theseus. In tandem adults fly very little and rest on vegetation.

DISCUSSION

Using the above sorts of information, I hope to present here a unified picture ofadaptive strategy in Morpho consistent with ecological and ethological theory. Thisaccount is not an attempt to reveal ecological and behavioral differences for allspecies of Morpho, but rather to synthesize the data for a few species. To do this, Iuse three appoaches: (1) extension of these findings to other species of Morpho, (2)relation of these findings to other aspects of Morpho ecology and ethology,especially oviposition strategy and larval behavior, and (3) portrayal of thesefindings within the context of the theory of fitness set and environmental grain asintroduced by Levins (1968). Other appoaches may be equally useful, but I feelthat synthesis is best achieved using these three directions.

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Table 5. Incidence of male-female encounters at feeding sites* and away fromfeeding sites in 3 species of Morpho.

Date Duration of ** no. of male-female encountersohs. period at feeding site away from feeding site

MORPHO AMATHONTE

0 20 00 10 00 40 20 00 2

MORPHO PELEIDES***

16 220 015 018 412 217 1

MORPHO THESEUS***

7 52 40 73 51 3

* A male-female encounter is defined here as a pursuit chase resulting in subsequentcourtship activity, or failing to so do.

** The first entry gives the amount of time spent at feeding sites while the second gives thetime spent searching for encounters away from feeding site.

*** Observations were conducted concurrently for these species.

Relations to other Morpho '

Three different adaptive strategies with respect to spacing pattern and courtshiphave been outlined in this paper. One of these, long distance circular movement ofmales on regular flight routes coupled with females waiting for them, is illustrated

Feb.

Mar.

July

Aug.

July

Aug.

12, 19701317202223202224

262729252628

262729252628

3.0/2.53.0/2.02.5/2.52.5/2.52.0/3.02.5/3.03.0/2.03.0/2.52.5/2.5

2.0/3.02.0/3.02.4/3.02.5/2.52.5/2.52.0/3.0

2.0/3.02.0/3.02.4/3.02.5/2.52.5/2.52.0/3.0

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by M. amathonte in lowland Central America. Another one, short distance circularmovement of both sexes with both sexes having very similar behavior patterns, istypified by M. theseus in Central American montane forests. The third strategy,long distance, erratic flight movements of both sexes and courtship encounters atfeeding sites, is characteristic of M. peleides in Central America at a wide range ofelevations. The question here, then, are these findings applicable to other species ofMorpho, most notably the South American fauna? I believe that there existspreliminary data for several other species suggesting generalization to them. Most ofthis information is very fragmentary and is summarized by H. Fruhstorfer in Seitz(1924). I rely heavily upon his early accounts of Morpho.

M. hebuca, M. perseus, and M. laertes are South American allies of M. theseus(Seitz, 1924). M. hebuca, the largest known Morpho, exhibits circular flight routesthat individuals keep for at least several days. A/, perseus does the same. As many as500-800 individuals of M. laertes have been seen floating along in an chain-likefashion on several days within the same area. These movements are similar to thoseobserved in M. theseus. Similar movement is shown by another ally, A/, catenarius,which is replaced in Central America byAf. polyphemus.

Circular flight movements of individuals, rather than groups of individuals as inM. theseus and it's South American allies, has been noted for several SouthAmerican allies of Af. amathonte. M. menelaus, M. rhetenor, and M. cypris showthis pattern of movement but it is not known if only males are involved. All ofthese species, however, have a well developed sexual dimorphism in wing colorationsimilar to that of M. amathonte. It is noteworthy that in M. rhetenor, females arefar less abundant locally than males and a figure of 10-15 females per 1000 males isgiven (Seitz, 1924).

Various species of the South American achilles group, of which M. peleides is amember (Seitz, 1924), are characterized by erratic flight movements and a localequal numerical abundance of both sexes. This has been noted for M. achilles, M.achillaena, M. vitrea, and M. granadensis. In all of these species, sexual dimorphismin wing coloration is weakly expressed. And like Af. peleides in Central America, Af.achilles is the most widespread and varied (many subspecies) Morpho in SouthAmerica.

The similarities in flight habits of several South America Morpho with theCentral American species discussed here suggest phylogenetic differences in adap-tive strategy at the level of species-groups. The rhetenor group (species such asAf.amathonte) is characterized by long distance circular flight movement with extremeregularity. The laertes group (species such as M. theseus) is characterized by shortdistance circular flight movement with a group home range. The achilles group ischaracterized by long distance erratic movement of individuals with no regularhome range for individuals (Af. amathonte) or groups (Af. theseus). The evolution-ary implications of these phylogenetic differences in ecological and ethologicalproperties are discussed elsewhere (Young & Muyshondt, 1972c).

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42 A.M. YOUNG

Relations to Oviposition and Larval Behavior

In Lepidoptera populations, patterns of adult dispersal and courtship strategy mustbe interpreted in part in terms of the temporal and spatial distribution of suitableoviposition sites and thus larval food plants. This point has been emphasized manytimes (Dethier, 1959; Ehrlich & Raven, 1965; Singer, 1972). Within a population ofa butterfly species, the spacing pattern of individuals for mating and ovipositiondepends upon the energy requirements of the individuals and the availability ofoviposition sites. Such factors are components of the "reproductive effort" of abutterfly (Labine 1968). They determine, to a large extent, the type of oviposition(single versus cluster), egg size, and clutch size per female in the population. Theymust also determine the survivorship curve of the species (Young, 1972c).

Superimposed upon these factors, there is predation and parasitism on immatu-res and adults. This is especially relevant for Morpho, since they are very large andconspicuous butterflies of presumably varying levels of palatability (Young, 1972a).Central American studies on the life cycles of Morpho (Young & Muyshondt,1972a, b) and similar South American studies (Otero, 1971; L.R. Otero, pers. -comms.) indicate wide evolutionary divergence in the type of oviposition and theextent of gregariousness during the larval period. These differences can be related todifferences in adult spacing patterns and courtship strategy among the three speciesstudied.

Various member species of the rhetenor group exhibit cluster oviposition (Seitz,1924). Otero (1971) has observed cluster oviposition inM anaxibia, a species veryclosely related to M. amathonte. The egg-laying habits of M. amathonte areundetermined, but cluster oviposition is highly suspected in this member of therhetenor group. Furthermore, larvae are gregarious in some South American mem-bers of the rhetenor group (Seitz, 1924; Otero, 1971; L.R. Otero, pers, comms.).Cluster oviposition and well developed larval gregariousness are considered veryspecialized ethological traits since they tend to concentrate pre-reproductive lifestages of butterflies in small areas of habitat. This in turn implies the evolution ofdefensive mechanisms to prevent an entire group of larvae from being killed bypredators. Such defense could be in the form of cryptic coloration of larvae,effective collective defense movements of larvae and perhaps coupled to collectiveemission of chemical secretions, or for unpalatable species, the acquisition of guadywarning coloration, Unpalatability may also be manifested through defense chemi-cal secretions. Cluster oviposition implies a concentration of reproductive effortover a single or few food plants (Labine, 1968). Otero (per. comms.) had observedthat various Morpho with cluster oviposition lay eggs on large adult trees (Legumi-noseae and Menispermaceae). Such food plants provide enough food for largegroups of larvae to complete development.

Cluster oviposition and larval gregariousness is probably present in M. theseus.Again, Otero (pers. comms.) has seen very pronounced egg clustering and largegroups of larvae in several Brazilian species of the laertes group, including M.laertes, M. perseus, M. richardus, M. athena, and M. hercules.

The specializations of egg clustering and larval gregariousness on food plants

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facilitate the integration of these species into stable primary-growth lowland wetforest communities (Young & Muyshondt, 1972c). M. theseus also probably lays itseggs on large adult forest trees. The spatial pattern of potential larval food plants inboth M. amathonte and M. theseus is probably such that individual trees are locallyrare through hyperdispersion. Under the spacing pattern and courtship strategy ofM. amathonte, mated females are likely hyperdispersed according to the distribu-tion of food plants. Cluster oviposition therefore permits the concentration ofreproductive effort over one of few individual trees per female. This cuts down onthe amount of energy expenditure and time necessary to locate food plants if M.amathonte possessed single oviposition and where only a few eggs are desposited inany one tree by a single female. Similarly in M. theseus, several mated females withina single group home range can find adequate amounts, of oviposition sites on one ora few adult trees for the support of many larvae. Thus while the occurrence of acohesive group home range gives a patchy distribution to M. theseus populations,the distribution and abundance of the patches is determined by the distribution oftree food plants. A single large tree can support several clutches of eggs laid by thesame female or several females and this allows for high adult populations cohesive-ness over small areas of habitat.

Young & Muyshondt (1972a) have found single oviposition in natural popula-tions of M. peleides in Costa Rica and El Salvador. Cluster oviposition does notoccur in natural populations. Larvae always occur singly on food plants. Otero(pers. comms.) has observed single oviposition in other species of the achilles groupin the Amazon Basin of Brazil, most notably M. achilles, M. deidamia, and M.violacea. Young & Muyshondt (1972a) have noted that when confined females ofM. peleides are forced to lay many eggs on a few leaves of a food plant (e.g. Mucunaurens), the first instar larvae disperse almost immediately upon hatching. A tenden-cy for larvae to aggregate on leaves is completely absent inM peleides. Virtually allthe larval food plants of M. peleides in Costa Rica and El Salvador are vines or veryyoung seedlings of certain leguminous tree species; oviposition on very large vinesor adult trees is virtually non-existent (Young & Muyshondt, 1972a). All of thesefactors point to a strategy of colonization on second-growth vegetation by M.peleides. Single oviposition, non-gregarious larvae, broad food plant specificity, andpreference for vines and young trees are ethological and ecological traits allindicative of a colonizing trait being present in M. peleides populations. Up to 10larval food plants are known for M. peleides from one locality in central Costa Rica(Young & Muyshondt, 1972a; Young 1972a). There traits are also consistent withthe spacing pattern of the adult population; high individual vagility and irregularday-to-day flight movements are very suggestive of population mobility associatedwith colonization. I suggest that perhaps the majority of species in the achillesgroup exhibit similar strategies of habitat exploitation.

Theory of Fitness and Environmental Grain

As an outgrowth of our concept of the ecological niche as a multidimensionalhyperspace (Hutchinson, 1959; Levins, 1968b), we can ask the basic question: how

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is the evironment broken up for different species of Morpho? Given their apparent-ly very different evolutionary origins, how have various ecological factors moldedadaptive strategies in breeding populations of each species? We expect differentstrategies of resource utilization because the butterflies studied here differgraetly in various morphological, ecological, and ethological traits. It is very usefulto frame such questions within the concepts of "fitness set" (Levins, 1963) and"environmental grain" (Levins, 1968a). The fitness set concept concerns thefitness of different genotypes of phenotypes on two environments: a convexfitness set implies a single optimal genotype or phenotype in both environ-ments, while the concave fitness set implies polymorphism, with one morphbeing optimal in one environment (Levins, 1968a). Environmental grain refersto the pattern of resource exploitation by individuals within a population:the environment is "fine-grained" with respect to a given resource if individualsgenerally spend their life in several patches ofthat resource (Levins, 1968a). On theother hand, if individuals tend to spend their entire life span within a single patchof the resource in question, the environment is said to be "coarse-grained" (Levins,1968a,b). The habitat of a species can be fine-grained with respect to some essentialresources and coarse-grained for other resources. Within a breeding population of aspecies, natural selection operates to achieve a level of optimal fitness within thepopulation, where phenotypes represent evolutionary compromises between fine-grained and coarse-grained selective forces.

Table 6 summarizes the predicted niche strategies and patterns of environmentalgrain for four different resources that are components of the niche requirements ofMorpho butterflies. This table represents a model of ecological adaptation inMorpho and is a direct outgrowth of the data given earlier on various ecological andethological traits in three species. As a model, it is hoped that it has predictive valueto other species of Morpho as well.

Specialization as members of stable ecological communities is the predictedadaptive or niche strategy of M. amathonte in tropical wet lowlands and also forMtheseus in mountains (Table 6). Being specialized species, polymorphism is predic-ted to prevail and with the fitness set being concave, i.e., one specialized genotypeon phenotype in different habitats. Superimposed upon this genetic structurewould be different patterns of environmental grain for different resources (Table6). The grain of the environment with respect to adult food source is certainlycoarse for male M. amathonte and both sexes of M. theseus. This is a direct result ofthe well-structured and high regularity of individual male movement around afood source in M. amathonte and the regular group movement home range patternwhich prevails in populations of M. theseus. Individuals in both cases tend toremain in the same area throughout their life and feed on a single major foodsource. Oviposition sites are probably anywhere from fine to coarse-grained formated females of M. amathonte, owing to the hyperdispersed distribution of theseindividuals: if she is far from a food plant patch, the oviposition strategy willbe more of a fine-grained nature. The very compact nature of adult populationsof M. theseus where females are included in group home ranges, indicates thatoviposition sites are a coarse-grained resource for mated females in this species.

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Table 6. Major ecological-evolutionary adaptive strategies in Morpho, as illustratedby three Central American species.

Species

M. amathonte

M. theseus

M. peleides

Nichestrategy

specialized

specialized

generalized

Fitnessset

Concave

Concave

Convex

Environmentalresource

Adult (d) foodoviposition sitemate encounterlarval food



Grain of envt'lresource

Coarsefine-to-Coarsefine-to-CoarseCoarse

CoarseCoarseCoarseCoarse

finefinefineCoarse

Food sources of larvae must, of course, be coarse-grained for all species sincelarvae are fixed on food plants by the oviposition strategy. Similar argumentsapply to acquisition of a mate as an environmental resource. From the standpointof male M. amathonte, an encounter with a receptive female can vary greatlyin terms of frequency: an individual male may only mate once in his life time (thusfemales are a coarse-grained resource) or several times (thus females are a fine-grained resource). Again, the probability of encounter is dependent upon the patternof hyperdispersion of the females. It is possible that several females may patrol theflight path of a single male. Further study needs to elucidate the interestingpossibility of pblygynous mating systems in territorial species such asM amathonte.The theory of polygyny and its evolutionary implications have been reviewed forbirds and mammals (Orians, 1969), but nothing is known about the occurrence of itin the invertebrates. Preferential mating of several females to a single male ofM. amathonte could be the result of accident or else the result of a well-structuredsystem of polygyny. As with oviposition strategy, mate encounter may vary from fineto coarse-grained in populations of M. theseus (Table 5). Again, the localization ofboth sexes to group home ranges offers the opportunity for males to mate withseveral different females during their life time. But if a well-structured socialhierarchy exists with polygynous mating females may be a coarse-grained resourcefor certain males within a group home range. In the absence of preferential mating,females would be a fine-grained resource for males.

A high amount of genetic variability, monomorphism, and physiologicalflexibility has been predicted to be present in populations of M. peleides throughout

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Central America (Young & Muyshondt, 1972a,c). The maintenance of suchvariability within populations is part of the adaptive strategy of a convex fitnessset (Table 6). A convex fitness set implies that a population is genetically orphysiologically able to respond to different habitat and micro-habitats pre-ferences; such would be the case in species with a strong history of coloni-zation. Also important for a colonizing species is the ability to pass throughmany patches of a given resource, and this is, of course, a result of selectionfor high vagility of individuals. Thus the environment tends to be fine-grainedfor pertinent resources (Table 6). The second-growth habitat tends to benon-patchy with respect to the spatial distribution of larval food plant species; vinessuch as Mucuna and Machaerium, two major food plants of M. peleides (Young &Muyshondt, 1972a) are usually present in large amount and a single vine may coverseveral meters of habitat. Mated females in search of oviposition sites encounterthese food plants in a fine-grained fashion. Likewise, high adult vagility permitsindividuals to pass through many different feeding sites during the course of a singleday's flight movement, and from day-to-day, the feeding sites visited also vary.Mate encouter from the standpoint of males must also be a fine-grained resource;since individual males meet several females at or near feeding sites. The lack of awell-structured system of flight movement in this Morpho suggests the lack ofpolygynous mating system and preferential mating may not be well-expressed. Thusall males initially possess the same capacity to mate with females, and the latter arefine-grained to all of them.

The patterns of ecological and ethological adaptation given in Table 6 illustratenicely how different species within a single animal genus may diverge greatly underdifferent selection pressures. The genus Morpho provides an interesting and usefulmodel for understanding different strategies of adaptation within a single genus.And while I do not wish to advocate that similar patterns of evolutionary diversifi-cation in ecological and ethological traits occur in other animal groups, I do wish topoint out the value of comparative studies among species within a genus. Ratherthan examining morphological differences alone, it is useful to study ecological andethological components of the pheyotype as well; this lesson is well learned withMorpho. The elucidation of differences in ecological and ethological traits ofdifferent species within a genus lays the groundwork for electrophoretic studies ofgenetic (enzyme) variability patterns within populations of the species being stud-ied. Detailed study of these traits can provide insight into patterns of geneticvariability in natural populations, already studied in selected invertebrates (e.g.Lewontin & Hubby, 1966; Burns & Johnson, 1967; Manwell et al., 1967; Johnsonet al., 1969). For example, this paper has attempted to present major ecological andethological differences among M. amathonte, M. theseus, and M. peleides in CentralAmerica. One important result of this survey is the prediction of low geneticvariability within breeding populations of M. amathonte and M. theseus and highvariability for M. peleides. Pilot studies are now in progress to seek those enzymesystems (e.g., esterases, dehydrogenases, etc.) which would be useful to test thishypothesis of genetic structure in populations of different species of Morpho.

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SUMMARY

(1) Adult population cohesiveness, habitat selection, diurnal activity periods, andcourtship strategies are examined for three species of Central American Morphobutterflies. Two of these species, M. amathonte and M. theseus are primary-growthforest butterflies, while M. peleides, the third species studied, is most characteristicof disturbed second-growth plant communities.

(2) Adult population cohesiveness, as a measurement of spacing pattern or popula-tion dispersion, is studied through the technique of mark-resighting analyses ofadult butterflies at natural and experimental food sources in natural habitats.

(3) Major differences in the ecological and ethological traits listed in (1) arepredicted for these species of Morpho since they differ greatly in the extent ofsexual dimorphism in the dorsal coloration of the wings. This morphologicalvariable among these species suggests the existence of differences in courtshipstrategy and the spacing pattern of adults associated with mating.

(4) Spacing pattern, adult population cohesiveness, and courtship strategy are heldto be major ecological and ethological traits having special importance on theadaptation of Morpho in tropical communities, most notably in terms of thetemporal and pattern of exploitation of oviposition sites and larval food plants.

(5) M. amathonte, as a specialized species of lowland wet forests, possesses tightadult population cohesiveness for at least the male members of breeding popula-tions. This population cohesiveness is characterized by a well-structured highlyregular system of individual male flight movement which disperses these individualsover large but consistent (from day-to-day) tracts of habitat in search of unmatedfemales. Diurnal activities of feeding, flight, courtship, and resting are well orderedin males of this species. The well-developed sexual dimorphism in this species,where the female is partially cryptic, allows the females to adopt a waiting strategyfor mate encounter with males along the latter's flight routes.

(6) M. theseus, a specialized species of montane wet forests, possesses tight adultpopulation cohesiveness for both sexes and which differs greatly from that of M.amathonte. Here, individuals of both sexes share a group home range whoseboundaries are very consistent from day-to-day. Presumably all adult activities,including feeding and courtship, take place within the group home range. Unlike M.amathonte, there are no individual male flight routes and the group home range isconsiderably smaller than a single male flight route in the former species. The lackof sexual dimorphism in wing coloration in this Morpho necessitates the closeproximity of individuals of both sexes in the same habitat in order to minimize thelong-distance visual discrimination undoubtedly characteristic of M. amathonte.While both species are very specialized, it is believed that differences in the spatialdistribution of oviposition sites and larval food plants between lowland and mon-

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48 A.M. YOUNG

tane forests accounts for this difference in spacing pattern and courtship strategy.Like M. amathonte, adult activities in M. theseus are well-ordered on a daily basis,but less is known about them.

(7) M. peleides is a non-specialized species of second-growth habitats over a rangeof elevations and as such, there is very loose adult population cohesiveness anderratic day-to-day individual movement in both sexes. Breeding populations tend tobe large and very mobile and they lack the well-structured regular home rangemovement seen in M. amathonte and M. theseus. The extent of sexual dimorphismin wing coloration is intermediate between M. amathonte and M. theseus, and itapplies the operation of visual cues over short distances at the major site forcourtship, namely feeding sites. Feeding sites function to concentrate males andreceptive females over small areas of habitat where they have an increased likeli-hood of meeting; in the absence of such a mechanism, mate encounter would beconsiderably lowered in the large and highly-dispersed populations of this species.Males and females frequently feed together at food sources and the vagility ofmated females is probably greater than unmated females, since the former indivi-duals search for oviposition sites over large areas and habitat. Oviposition sites andlarval food plants, being mostly vines and small seedlings, tend to have a less patchydistribution than the food plants (large adult trees) of M. amathonte and M. theseusin forests. As a generalized species, oviposition is single in M. peleides and verylikely clustered in the other two species. Being members of the rhetenor and laertesgroups, larval gregariousness also probably occurs regularly in M. amathonte and M.theseus respectively, while absent in M. peleides.

(8) The above findings are discussed in terms of the recent ecological concepts ofthe fitness set and environmental grain. Specialized species such as M. amathonteand M. theseus are believed to possess concave fitness sets which adapt them togenerally coarse-grained resources while generalized species like M. peleides ispredicted to be experiencing fine-grained selection on a concave fitness set.

ACKNOWLEDGEMENTS

The research summarized in this paper, spanning a three-year period, was funded throughvarious sources: N.S.F. Grant GB-7805 (Daniel H. Janzen, principal investigator), 1970; CollegeScience Improvement Grant (COSIP) GY4711 (Lawrence University), 1971; Bache Fund GrantNo. 521 of the National Academy of Sciences and N.S.F. Grant GB-33060, both awarded tothe author (1972). The author is very grateful for all of this support. Logistic and laboratorysupport was provided during 1970 by The Organization for Tropical Studies, Inc., and in1971-1972 by the Costa Rican Field Studies Program of the Associated Colleges of theMidwest. Patrick Eagan (Lawrence) assisted with the 1971 field work, and Roger Kimber andJohn Thomason (Lawrence) assisted in 1972. Malcolm Barcant (Port-of-Spain, Trinidad),Alberto Muyshondt (San Salvador), and Luiz R. Otero (Rio de Janeiro) generously providedhelpful information on the ecology and behavior of Morpho, which assisted greatly in theformation of the ideas presented in this paper.

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LITERATURE

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Author's address: Allen M. Young, Department of Biology, Lawrence University, Appleton,Wisconsin 54911, U.S.A.

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