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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 x
mmxx = = 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 Thus, theory predicts that early maturation at a small size will be associated with low survival of juveniles.size 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 jarrovi
Sceloporus graciosusSceloporus graciosus
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 jarrovi
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+
SV
L (m
m)
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
hig
h
low
hig
hS. 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 SizeF
itne
ss o
f offs
pri
ng
Fitn
ess
of o
ffsp
rin
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)
Fem
ale
SV
L (m
m)
50
55
60
65
70
75
80
85
Variation in Female SizeVariation in Female Size
New Jersey VirginiaSouth Carolina
Indiana
Florida
Oklahoma
FL IN
Eg
g W
eig
ht (
g)
0.1
0.2
0.3
0.4
0.5
0.6
0.7
New Jersey
Virginia
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.
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
Ca
lori
es
per
g
ram
of e
gg
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.