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

2. Life History Traits Age at MaturityAge at Maturity Size at MaturitySize at Maturity Number of OffspringNumber of Offspring Size of OffspringSize of Offspring Frequency of ReproductionFrequency of Reproduction x = age  = age at maturity l x = survival to age x m x = fecundity to age x

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

4. 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

5. Donald W. Tinkle University of Michigan Life Histories of Lizards

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

7. Life History Problems When should I reproduce?When should I reproduce? How much should I reproduce?How much should I reproduce?

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

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

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

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

12. BurdenSurvivalEndurance “Costs” of Reproduction The survival of manipulated females (86%) was higher than the survival of control females (62%).

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

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

15. 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. 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] Cambridge University Press]

16. Thermal Clines in Body Size 132 Body size Environmental temperature

17. Sceloporus occidentalis Sceloporus merriami Sceloporus undulatus Sceloporus jarrovi Sceloporus graciosus

18. 1000 KM KS NE WCO ECO UT AZ NM 1 NM 2 TX OH NJ SC AL GA MO MS Study Sites

19. hyacinthinusgarmanicowlesitristichusconsobrinustedbrowni Subspecies of Sceloporus undulatus

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

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

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

23. Sceloporus occidentalis Sceloporus merriami Sceloporus undulatus Sceloporus jarrovi Sceloporus graciosus

24. The Sagebrush Lizard (Sceloporus graciosus)

25. Thermal Cline in Size [Source: Sears & Angilletta, in review for Integr. Comp. Biol.] Warmerenvironment Coolerenvironment

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

27. Lizards at high elevation grow faster not longer.

28. Overview of Life Histories low high Elevation low high Latitude Survival Growth rate Thermalopportunity Survival Thermalopportunity low high low high S. graciosus S. undulatus

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

30. Life History Problems When should I reproduce?When should I reproduce? How much should I reproduce?How much should I reproduce?

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

32. CA (manipulated) WA Experimental manipulation of clutch size reveals a tradeoff. [Source: Sinervo 1999, American Naturalist 154: S26-S42]

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

34. Bigger eggs in Colder Environments

35. Variation in Female Size New Jersey Virginia South Carolina Indiana Florida Oklahoma FLIN

36. New Jersey Virginia South Carolina Indiana Florida Oklahoma NJSC Variation in Egg Size

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

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

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

40. Can females compensate for smaller eggs?

41. Egg Mass Calories per gram of egg

42. Causes of Egg SizeClines Theory predicts that egg size should be altered according to environments conditions, but females should make eggs of a constant size.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.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.Both adaptive and non-adaptive explanations account for this variation in eggs size.

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