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Life history and dispersal

Life history and dispersal. Life history evolution Reproductive value Dispersal Inbreeding depression Kin recognition. Age-specific population growth. Age-specific survivorship (l x ) Age specific reproduction (m x ) Net reproductive rate: R o = S l x m x

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Life history and dispersal

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  1. Life history and dispersal • Life history evolution • Reproductive value • Dispersal • Inbreeding depression • Kin recognition

  2. Age-specific population growth • Age-specific survivorship (lx) • Age specific reproduction (mx) • Net reproductive rate: Ro = S lxmx • Stable population: Ro = 1 • Growing population: Ro > 1 • Declining population: Ro < 1

  3. The age-specific survival (lx) and fertility (mx) pattern specifies an organism’s life history pattern.

  4. Estimating Survivorship (lx) (lx)

  5. Survivorship types

  6. Survivorship curve examples

  7. Fertility (mx) patterns

  8. Life history trade-offsexpected with limited resources Lizards Birds Due to allocation of resources between maintenance and reproduction

  9. Reproductive value (Fisher) • Age-specific expectation of offspring (how much is a female worth in terms of future offspring?) • Assuming a stable population (R = 1) • Vx = (St=xmt lt)/lx • the number of female offspring produced at this moment by females of age x or older / the number of females which are age x at this moment • Reproductive value peaks near puberty in human populations

  10. Beetle Reproductive value curves Lizards Crustacea

  11. Evolutionary theory of aging • The risk of mortality should influence life span because the force of natural selection declines with age, i.e. older individuals contribute fewer offspring to the future than younger individuals • Consequently, mutations with late-acting deleterious effects will not be eliminated (antagonistic pleiotropy) • Senescence should result and shorten life span in proportion to mortality risk • Expect that investing in early reproduction will detract from survival - the “disposable soma” idea

  12. Species means Independent contrasts F 1,40 = 7.3, P = 0.01 F 1,62 = 1.5, P = 0.23 Longevity (y) Change in longevity (log y) Body mass (g) Change in body mass (log g) Allometric relationship for 463 spp of nonflying placental mammals (Austad & Fischer 1991) Longevity in bats Myotis brandti (38 yrs, 8 g) Myotis lucifugus (34 yrs, 7 g) Myotis blythii (33 yrs, 23 g) Rhinolophus ferrumequinum (31 yrs, 24 g)

  13. Reproductive effort and longevity in bats Rhinolophus darlingi Nyctophilus gouldi 1 pup/yr 2 pups/yr Species Contrasts (a) (b) Change in longevity (log y) Longevity (y) F 1,62 = 23.6, P = < 0.0001 F 1,40 = 19.4, P = < 0.0001 Reproductive rate Change in reproductive rate

  14. Questions • Opossums typically reproduce once and then die, but some island populations reproduce twice before dying. Provide an evolutionary explanation for this difference. • If a female lion was in a position to help either its adult sister or its mother, which would you expect it to help and why?

  15. Dispersal

  16. Why disperse from home? • Avoid inbreeding (and outbreeding?) • either sex should leave • must recognize and avoid mating with kin • E.g., inbreeding avoidance in kibbutzim • Reduce competition • dispersal should occur in sex with greatest competition for mates, e.g. males in polygynous species

  17. Drosophila subobscura Deer mice Inbreeding depression Reduction in survival or reproduction caused by production of offspring homozygous for deleterious genes

  18. Kin recognition • Familiarity with spatial location • e.g. treat all offspring in nest as own • Template matching • Can be learned or innate • Requires cues with sufficient variation to permit estimation of relatedness • Innate cues involve olfaction and MHC

  19. Multiple Histocompatibility Complex • MHC is involved in cell-cell recognition, used by immune system to recognize foreign antigens • Contains many loci which exhibit high levels of heterozygosity with many alleles • Implicated in kin recognition from tunicates to humans • Human leukocyte antigen (HLA) on chr 6

  20. Exposure to different MHC genotype causes spontaneous abortions in mice

  21. Dissassortative mating by MHC in mice and humans

  22. Why disperse from home? • Avoid inbreeding (and outbreeding?) • either sex should leave • must recognize and avoid mating with kin • E.g., inbreeding avoidance in kibbutzim • Reduce competition • dispersal should occur in sex with greatest competition for mates, e.g. males in polygynous species

  23. Oedipus hypothesis: parents expel offspring to reduce competition

  24. Natal dispersal in birds and mammals

  25. Natal dispersal is male-biased in polygynous mammals

  26. Natal dispersal summary • Dispersal in birds and mammals is associated with the mating system • resource defense = female dispersal • female defense = male dispersal • Inbreeding avoidance together with reduction of competition for mates best explains sex-biased dispersal patterns

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