Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Click to edit Master subtitle style 1/12/13 Chapter 12After conception: the evolution of life history and parental care1/12/13 Variation in life history traits1/12/13 Evolution of life history traits•Life history traits involved in trade-offs–Limited amount of energy to invest in survival, maintenance, and reproduction•Natural selection expected to optimize in light of trade-offs–Maximize number of offspring surviving to maturity–Depends on likelihood of survival to different age classes1/12/13 Data from opossums supports predictions from life history theory1/12/13 Predation risk drives life history evolution in guppies1/12/13 Transplant experiments demonstrate rapid evolution of life history traits1/12/13 Key Concepts•Trade-offs arise when investment in one trait result in lower investment in another trait•Investment in reproduction is often at the expense of investment in growth or maintenance•Selection may favor alleles that are beneficial early in life, even if they are deleterious late in life•Investment in early reproduction often reduces reproduction late in life1/12/13 Parental investment•Females are more likely than males to provide parental care–Males have less investment–Males have uncertain paternity1/12/13 Sex role reversalFemales compete over access to males1/12/13 Sex role reversal in pipefish1/12/13 Adjusting the family•Organisms may regulate the number of offspring to maximize fitness–Miscarriage–Cannibalism•Organisms may regulate the sex ratio to maximize fitness1/12/13 Why are sex ratios often balanced•Frequency-dependent selection–Production of each sex favored when rare–Rare sex has more mating opportunities1/12/13 Trivers-Willard hypothesis•Mothers alter sex ratio depending on condition–Females in poor condition–Males in good condition; males likely to benefit more from being large1/12/13 Sex ratio adjustment in Seychelles warblers•Females favored with high resources–Up to three helping daughters beneficial•Males favored with low resources–Disperse away from poor habitat1/12/13 Fig wasps produce female-biased sex ratiosMales mate with sisters; a single male can inseminate multiple females1/12/13 Some species switch sex in predicted mannerStart as females, but switch to male when they are large1/12/13 Conflict over parental care•Strategies to maximize offspring produced over a lifetime can differ for the sexes1/12/13 Genomic imprinting•Gene expression silenced by methylation by one parent–Offspring express either maternal or paternal copy of gene, but not both1/12/13 Genomic imprinting and parental conflict•Fathers favor more investment in current offspring–Future offspring not likely to be his•Mothers favor less investment than father–Save for future reproduction1/12/13 Rapid evolution of Igf2 in guppies with placentas1/12/13 Key Concepts•Females generally benefit more than males from providing parental care–Exceptions provide exciting tests•Frequency-dependent selection can lead to balanced sex ratios•Predictions of the Trivers-Willard hypothesis–Produce females in poor condition–Males in good condition1/12/13 Key Concepts•Parental care is often rife with conflict–Sexes may maximize fitness differently•Males benefit when mother invests more in current offspring; females benefit by saving resources for future offspring•Parental conflict can lead to battles of gene expression in offspring1/12/13 Postponing senescence•Calorie restriction can slow the aging process–Genes involved in repair switched on under stress•May involve trade-offs–Worm mutants that age more slowly have lower fitness1/12/13 Key Concept•Senescence results from a trade-off between reproduction early in life and longevity1/12/13 Menopause: trade-off or adaptation?•Menopause may be adaptive–Older females benefit from rearing current children or helping rear grandchildren•Menopause may be a life-history trade-off–Other species also have post reproductive lifespan–May be more common than currently known1/12/13 Key Concepts•Menopause evolved after split from other apes•Menopause may be adaptive or simply a life-history