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 =  l x m x –Stable population: R o = 1 –Growing population: R o > 1 –Declining population: R o < 1

The age-specific survival (l x ) and fertility (m x ) pattern specifies an organism’s life history pattern.

Estimating Survivorship (l x ) (l x )

Survivorship types

Survivorship curve examples

Fertility (m x ) patterns

Life history trade-offs expected with limited resources Lizards Birds Due to allocation of resources between maintenance and reproduction

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) V x = (  t=x m t l t )/l x –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

Reproductive value curves Lizards Beetle Crustacea

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

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

Reproductive effort and longevity in bats Reproductive rateChange in reproductive rate Change in longevity (log y) Longevity (y) (a)(b) F 1,62 = 23.6, P = < F 1,40 = 19.4, P = < pup/yr2 pups/yr Rhinolophus darlingiNyctophilus gouldi Species Contrasts

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?

Dispersal

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

Inbreeding depression Reduction in survival or reproduction caused by production of offspring homozygous for deleterious genes Deer miceDrosophila subobscura

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

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

Exposure to different MHC genotype causes spontaneous abortions in mice

Dissassortative mating by MHC in mice and humans

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

Oedipus hypothesis: parents expel offspring to reduce competition

Natal dispersal in birds and mammals

Natal dispersal is male-biased in polygynous mammals

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