Life Histories I What is a Life History

Life Histories I. What is a Life History? II. Growth and Reproduction III. Offspring Size and Number

Life History Traits x = age at maturity lx = survival to age x mx = fecundity to age x • • • Age at Maturity Size at Maturity Number of Offspring Size of Offspring Frequency of Reproduction

Phrynosomatid lizards are excellent models for studies of life-history variation. • >100 species occurring in North & Central America • Occur at elevations from sea level to 4000 m • Size ranges from 4 to >30 g

Life Histories of Lizards 1. Early reproduction, large clutches, multiple clutches per year 2. Early Reproduction, small clutches, multiple clutches per year 3. Delayed reproduction, large clutches, single clutch per year 4. Delayed reproduction, viviparous, single brood per year Donald W. Tinkle University of Michigan

Life Histories of Lizards 1. Early reproduction, large clutches, multiple clutches per year 2. Early Reproduction, small clutches, multiple clutches per year 3. Delayed reproduction, large clutches, single clutch per year 4. Delayed reproduction, viviparous, single brood per year Donald W. Tinkle University of Michigan

The Life History of a Small Lizard Circles = eggs, Boxes = reproductive events

Life History Problems • When should I reproduce? • How much should I reproduce?

“Costs” of Reproduction • Physiological – Energy spent on gametes and offspring – Less room for food in body cavity • Behavioral – – Less opportunity to forage Compromise in thermoregulation Increased exposure to predators Decreased locomotor performance

Survival Costs of Reproduction • Surgically removed follicles to reduce the number of eggs that a female produces • Females in the folliclereduction group suffered less mortality and grew faster than females in the control group Tree Lizard (Urosaurus ornatus) [Source: Landwer 1994, Oecologia 100: 243 -249]

“Costs” of Reproduction Burden Endurance Survival [Source: Miles et al. 2000, Evolution 54: 1386 -1395]

“Costs” of Reproduction [Source: Miles et al. 2000, Evolution 54: 1386 -1395]

“Costs” of Reproduction Burden Endurance Survival The survival of manipulated females (86%) was higher than the survival of control females (62%). [Source: Miles et al. 2000, Evolution 54: 1386 -1395]

When should a lizard reproduce? Benefits of earlier maturity Higher survival to maturity Shorter generations Benefits of later maturity Higher fecundity through longer growth Higher offspring success through experience [Source: Stearns 1992, The Evolution of Life Histories, Oxford University Press]

The Life History of a Small Lizard Circles = eggs, Boxes = reproductive events

Predictions of Theory If the rate of mortality increases, age at maturity should decrease and the effort invested in reproduction should increase. Thus, theory predicts that early maturation at a small size will be associated with low survival of juveniles. [Source: Charlesworth 1980, Evolution in Age-structured Populations, Cambridge University Press]

Thermal Clines in Body Size 2 Body size 1 Environmental temperature 3

Sceloporus graciosus Sceloporus jarrovi Sceloporus merriami Sceloporus occidentalis Sceloporus undulatus

Study Sites NJ NE UT KS WCO MO OH ECO AZ NM 1 SC NM 2 TX 1000 KM MS AL GA

hyacinthinus garmani tedbrowni cowlesi consobrinus Subspecies of Sceloporus undulatus tristichus

Thermal Cline in Size [Source: Angilletta et al. , in review for American Naturalist]

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

Low mortality favors delayed maturation. [Source: Angilletta et al. , in review for American Naturalist]

Sceloporus graciosus Sceloporus jarrovi Sceloporus merriami Sceloporus occidentalis Sceloporus undulatus

The Sagebrush Lizard (Sceloporus graciosus)

Thermal Cline in Size Cooler environment Warmer environment [Source: Sears & Angilletta, in review for Integr. Comp. Biol. ]

GCK FPK Site CCC Elev (m) Clear Creek Canyon 1752 Firepit Knoll 1961 Goose Creek Knoll 2255

Lizards at high elevation grow faster not longer.

S. graciosus S. undulatus Survival high Overview of Life Histories Survival Thermal opportunity low Growth rate high low Elevation Growth rate high low Latitude

Causes of Size Clines • Theory predicts delayed maturation and large size in environments where survival of juveniles is high. • Sceloporus undulatus is larger in colder environments because high survival of juveniles favors delayed maturation. • Sceloporus graciosus is larger in colder environments because low survival of small juveniles favors rapid growth.

Life History Problems • When should I reproduce? • How much should I reproduce?

Fitness of offspring Optimal Offspring Size of offspring [Source: Smith & Fretwell 1974, American Naturalist 108: 499 -506]

Experimental manipulation of clutch size reveals a tradeoff. CA CA WA (manipulated) [Source: Sinervo 1999, American Naturalist 154: S 26 -S 42]

Variation in Egg Size • Egg size varies greatly within and among species • Many factors can account for variation: – Environmental temperature – Resource availability – Constraints (physiological or morphological)

Bigger eggs in Colder Environments

Variation in Female Size Indiana New Jersey FL IN Virginia South Carolina Florida Oklahoma

Variation in Egg Size NJ SC Virginia New Jersey Indiana South Carolina Florida Oklahoma

Morphological Constraints Photo by: Wendy Hodges http: //www. digimorph. org/specimens/Phrynosoma_cornutum/whole/

Size of the egg is constrained by size of the pelvis. Photo by: Wendy Hodges http: //www. digimorph. org/specimens/Phrynosoma_cornutum/whole/

Large eggs may not fit through the pelvis. Photo by: Wendy Hodges http: //www. digimorph. org/specimens/Phrynosoma_cornutum/whole/

Can females compensate for smaller eggs?

Egg Mass Calories per gram of egg

Causes of Egg Size. Clines • Theory predicts that egg size should be altered according to environments conditions, but females should make eggs of a constant size. • In Sceloporus undulatus, the size and composition of eggs varies among populations in different environments. • Both adaptive and non-adaptive explanations account for this variation in eggs size.

Todd Steury Chris Oufiero Art Dunham Adam Leaché Peter Niewiarowski Mike Sears