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Life Histories

Life Histories. I. What is a Life History? II. Growth and Reproduction III. Offspring Size and Number. Age at Maturity Size at Maturity Number of Offspring Size of Offspring Frequency of Reproduction. Life History Traits. x = age  = age at maturity l x = survival to age x

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Life Histories

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

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

  3. Phrynosomatid lizards are excellent modelsfor 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

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

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

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

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

  8. 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 “Costs” of Reproduction

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

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

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

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

  13. Benefits of earlier maturity Higher survival to maturity Shorter generations Benefits of later maturity Higher fecundity through longer growth Higher offspring success through experience 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. 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. Predictions of Theory [Source: Charlesworth 1980, Evolution in Age-structured Populations, Cambridge University Press]

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

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

  18. Study Sites NJ NE KS MO OH WCO UT ECO AZ SC NM2 NM1 GA AL MS TX 1000 KM

  19. hyacinthinus garmani tedbrowni cowlesi consobrinus tristichus 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 graciosus Sceloporus jarrovi Sceloporus merriami Sceloporus undulatus Sceloporus occidentalis

  24. The Sagebrush Lizard(Sceloporus graciosus)

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

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

  27. Lizards at high elevation grow faster not longer.

  28. Overview ofLife Histories S. graciosus S. undulatus Survival Growth rate high high Growth rate Survival Thermal opportunity Thermal opportunity low low high high low low Elevation Latitude

  29. 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. Causes of Size Clines

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

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

  32. CA (manipulated) CA 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 species • 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 Indiana FL IN New Jersey Virginia South Carolina Florida Oklahoma

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

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

  40. Can females compensate for smaller eggs?

  41. Calories per gram of egg Egg Mass

  42. 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. Causes of Egg SizeClines

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

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