Life HistoriesLife Histories

I. What is a Life History?I. What is a Life History?

II. Growth and ReproductionII. Growth and Reproduction

III. Offspring Size and NumberIII. Offspring Size and Number

Life History TraitsLife History Traits

• Age at MaturityAge at Maturity• Size at MaturitySize at Maturity• Number of OffspringNumber of Offspring• Size of Offspring Size of Offspring • Frequency of Frequency of

ReproductionReproduction

l mx xx

x

xx = age= age = age at maturity= age at maturityllxx = = survival to age xsurvival to age xmmxx = = fecundity to age xfecundity to age x

Phrynosomatid lizards are excellent modelsPhrynosomatid lizards are excellent modelsfor studies of life-history variation.for studies of life-history variation.

• • >>100 species occurring in 100 species occurring in North & Central AmericaNorth & Central America• • Occur at elevations from Occur at elevations from sea level to 4000 m sea level to 4000 m • • Size rSize ranges from 4 to >30 ganges from 4 to >30 g

1.1. Early reproduction, large clutches, Early reproduction, large clutches, multiple clutches per yearmultiple clutches per year

2.2. Early Reproduction, small clutches, Early Reproduction, small clutches, multiple clutches per yearmultiple clutches per year

3.3. Delayed reproduction, large clutches, Delayed reproduction, large clutches, single clutch per yearsingle clutch per year

4.4. Delayed reproduction, viviparous, single Delayed reproduction, viviparous, single brood per yearbrood per year

Donald W. TinkleDonald W. TinkleUniversity of MichiganUniversity of Michigan

Life Histories of LizardsLife Histories of Lizards

1. Early reproduction, large clutches, Early reproduction, large clutches, multiple clutches per yearmultiple clutches per year

2.2. Early Reproduction, small clutches, Early Reproduction, small clutches, multiple clutches per yearmultiple clutches per year

3. Delayed reproduction, large clutches, Delayed reproduction, large clutches, single clutch per yearsingle clutch per year

4. Delayed reproduction, viviparous, single Delayed reproduction, viviparous, single brood per yearbrood per year

Donald W. TinkleDonald W. TinkleUniversity of MichiganUniversity of Michigan

Life Histories of LizardsLife Histories of Lizards

The Life History of a Small LizardThe Life History of a Small Lizard

Circles = eggs, Boxes = reproductive eventsCircles = eggs, Boxes = reproductive events

Life History ProblemsLife History Problems

• When should I reproduce?When should I reproduce?

• How much should I reproduce?How much should I reproduce?

““Costs” of ReproductionCosts” of Reproduction

• PhysiologicalPhysiological– Energy spent on gametes and offspringEnergy spent on gametes and offspring– Less room for food in body cavityLess room for food in body cavity

• BehavioralBehavioral– Less opportunity to forage Less opportunity to forage – Compromise in thermoregulationCompromise in thermoregulation– Increased exposure to predatorsIncreased exposure to predators– Decreased locomotor performanceDecreased locomotor performance

Tree LizardTree Lizard ((Urosaurus Urosaurus

ornatusornatus))

[Source: Landwer 1994, [Source: Landwer 1994, OecologiaOecologia 100: 243-249] 100: 243-249]

Survival Costs of ReproductionSurvival Costs of Reproduction

• • Surgically removed follicles to Surgically removed follicles to reduce the number of eggs reduce the number of eggs that a female producesthat a female produces

• • Females in the follicle-Females in the follicle- reduction group suffered less reduction group suffered less mortality and grew faster thanmortality and grew faster than females in the control groupfemales in the control group

BurdenBurden SurvivalSurvivalEnduranceEndurance

[Source: Miles et al. 2000, [Source: Miles et al. 2000, EvolutionEvolution 54: 1386-1395] 54: 1386-1395]

““Costs” of Costs” of ReproductionReproduction

““Costs” of Costs” of ReproductionReproduction

[Source: Miles et al. 2000, [Source: Miles et al. 2000, EvolutionEvolution 54: 1386-1395] 54: 1386-1395]

BurdenBurden SurvivalSurvivalEnduranceEndurance

[Source: Miles et al. 2000, [Source: Miles et al. 2000, EvolutionEvolution 54: 1386-1395] 54: 1386-1395]

““Costs” of Costs” of ReproductionReproduction

The survival of manipulated females (86%) was higherThe survival of manipulated females (86%) was higherthan the survival of control females (62%).than the survival of control females (62%).

Benefits of later maturityHigher fecundity through longer growthHigher offspring success through experience

Benefits of earlier maturityHigher survival to maturityShorter generations

When should a lizard reproduce?When should a lizard reproduce?

[Source: Stearns 1992, [Source: Stearns 1992, The Evolution of Life HistoriesThe Evolution of Life Histories, Oxford University Press], Oxford University Press]

The Life History of a Small LizardThe Life History of a Small Lizard

Circles = eggs, Boxes = reproductive eventsCircles = eggs, Boxes = reproductive events

Predictions of TheoryPredictions of Theory

If the rate of mortality increases, age at maturity should If the rate of mortality increases, age at maturity should decrease and the effort invested in reproduction should decrease and the effort invested in reproduction should increase.increase.

Thus, theory predicts that early maturation at a small size Thus, theory predicts that early maturation at a small size will be associated with low survival of juveniles.will be associated with low survival of juveniles.

[Source: Charlesworth 1980, [Source: Charlesworth 1980, Evolution in Age-structured PopulationsEvolution in Age-structured Populations,,

Cambridge University Press]Cambridge University Press]

Thermal Clines in Body SizeThermal Clines in Body Size

11 3322

Bod

y si

zeB

ody

size

Environmental temperatureEnvironmental temperature

Sceloporus occidentalisSceloporus occidentalis

Sceloporus merriamiSceloporus merriami

Sceloporus undulatusSceloporus undulatus

Sceloporus jarroviSceloporus jarroviSceloporus graciosusSceloporus graciosus

1000 KM

KS

NE

WCOECO

UT

AZ

NM1NM2

TX

OH

NJ

SC

AL GA

MO

MS

Study SitesStudy Sites

hyacinthinus garmani cowlesi tristichusconsobrinustedbrowni

Subspecies of Subspecies of Sceloporus undulatusSceloporus undulatus

Thermal Cline in SizeThermal Cline in Size

Environmental Temperature-6 -4 -2 0 2 4 6

Ave

rage

Bod

y Le

ngth

-10

-5

0

5

10

[Source: Angilletta et al., in review for [Source: Angilletta et al., in review for American NaturalistAmerican Naturalist]]

Body Temperature (oC)10 14 18 22 26 30 34 38 42

Rel

ativ

e P

erfo

rman

ce (%

)

0

20

40

60

80

100sprint speedenduranceenergy assimilation

[Source: Angilletta et al. 2002, [Source: Angilletta et al. 2002, Journal of Thermal Biology Journal of Thermal Biology 27: 199-204]27: 199-204]

Monthly Juvenile Survivorship-0.008 -0.004 0.000 0.004 0.008 0.012 0.016

Age

at M

atur

ity

-0.050

-0.025

0.000

0.025

0.050

Low mortality favors Low mortality favors delayed maturation.delayed maturation.

[Source: Angilletta et al., in review for [Source: Angilletta et al., in review for American NaturalistAmerican Naturalist]]

Sceloporus occidentalisSceloporus occidentalis

Sceloporus merriamiSceloporus merriami

Sceloporus undulatusSceloporus undulatus

Sceloporus jarroviSceloporus jarroviSceloporus graciosusSceloporus graciosus

The Sagebrush LizardThe Sagebrush Lizard((Sceloporus graciosusSceloporus graciosus))

Thermal Cline in SizeThermal Cline in Size

Length of activity season (d)120 140 160 180 200 220 240 260

Max

imum

adu

lt S

VL

(mm

)

55

60

65

70

75

[Source: Sears & Angilletta, in review for [Source: Sears & Angilletta, in review for Integr. Comp. Biol.Integr. Comp. Biol.]]

WarmerWarmerenvironmentenvironment

CoolerCoolerenvironmentenvironment

Site Elev (m)Site Elev (m)

Clear Creek Canyon 1752Clear Creek Canyon 1752

Firepit KnollFirepit Knoll 1961 1961

Goose Creek Knoll 2255Goose Creek Knoll 2255

GCKGCK

CCCCCC

FPKFPK

age class (yr)1 2 3+

SVL

(mm)

35

40

45

50

55

60

65

70

CCC FPK GCK

Lizards at high elevation grow faster not longer. Lizards at high elevation grow faster not longer.

Overview ofOverview ofLife HistoriesLife Histories

low high

ElevationElevationlow high

LatitudeLatitude

SurvivalSurvival

Growth rateGrowth rate

ThermalThermalopportunityopportunity

SurvivalSurvival

Growth rateGrowth rate

ThermalThermalopportunityopportunity

low

high

low

high

S. graciosusS. graciosus S. undulatusS. undulatus

Causes of Size ClinesCauses of Size Clines

• Theory predicts delayed maturation and Theory predicts delayed maturation and large size in environments where survival of large size in environments where survival of juveniles is high.juveniles is high.

• Sceloporus undulatusSceloporus undulatus is larger in colder is larger in colder environments because high survival of environments because high survival of juveniles favors delayed maturation.juveniles favors delayed maturation.

• Sceloporus graciosusSceloporus graciosus is larger in colder is larger in colder environments because low survival of small environments because low survival of small juveniles favors rapid growth.juveniles favors rapid growth.

Life History ProblemsLife History Problems

• When should I reproduce?When should I reproduce?

• How much should I reproduce?How much should I reproduce?

Optimal Offspring SizeOptimal Offspring SizeFi

tnes

s of

offs

prin

gFi

tnes

s of

offs

prin

g

Size of offspringSize of offspring

[Source: Smith & Fretwell 1974, [Source: Smith & Fretwell 1974, American Naturalist American Naturalist 108: 499-506]108: 499-506]

CA CA(manipulated)

WA

Experimental manipulation of clutch size reveals a tradeoff.Experimental manipulation of clutch size reveals a tradeoff.

[Source: Sinervo 1999, [Source: Sinervo 1999, American Naturalist American Naturalist 154: S26-S42]154: S26-S42]

Variation in Egg SizeVariation in Egg Size

• Egg size varies greatly within and among Egg size varies greatly within and among speciesspecies

• Many factors can account for variation:Many factors can account for variation:– Environmental temperatureEnvironmental temperature– Resource availabilityResource availability– Constraints (physiological or Constraints (physiological or

morphological)morphological)

Bigger eggs in Colder Bigger eggs in Colder EnvironmentsEnvironments

Fem

ale

SV

L (m

m)

50

55

60

65

70

75

80

85Variation in Female SizeVariation in Female Size

New Jersey VirginiaSouth Carolina

Indiana

Florida

Oklahoma

FL IN

Egg

Wei

ght (

g)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

New JerseyVirginia

South Carolina

Indiana

Florida

Oklahoma

NJ SC

Variation in Egg SizeVariation in Egg Size

Morphological Constraints

Photo by: Wendy Hodgeshttp://www.digimorph.org/specimens/Phrynosoma_cornutum/whole/

Size of the egg is constrained by size of the pelvis.

Photo by: Wendy Hodgeshttp://www.digimorph.org/specimens/Phrynosoma_cornutum/whole/

Photo by: Wendy Hodgeshttp://www.digimorph.org/specimens/Phrynosoma_cornutum/whole/

Large eggs may not fit through the pelvis.

Can females compensate for smaller Can females compensate for smaller eggs?eggs?

0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24 0.26

Egg Weight

4000

4200

4400

4600

4800

5000

5200

5400

5600

5800

6000

6200C

al/g

95% confidencer = -0.5511p < 0.001

Egg Mass

Cal

orie

s pe

r gr

am o

f egg

Causes of Egg SizeClinesCauses of Egg SizeClines

• Theory predicts that egg size should be Theory predicts that egg size should be altered according to environments altered according to environments conditions, but females should make eggs conditions, but females should make eggs of a constant size.of a constant size.

• In In Sceloporus undulatusSceloporus undulatus, the size and , the size and composition of eggs varies among composition of eggs varies among populations in different environments. populations in different environments.

• Both adaptive and non-adaptive Both adaptive and non-adaptive explanations account for this variation in explanations account for this variation in eggs size. eggs size.

Art DunhamChris Oufiero

Mike Sears

Todd Steury

Peter Niewiarowski

Adam Leaché