Life length and ageing Selection for increased life length? –Selection is strong prior to reproduction –Selection is relaxed thereafter What is ageing (senescence)? –Accumulation of mutations –Reduced selection after reproduction Reproduce once / several times? –Semelparity/monocarpy –Iteroparity/polycarpy

Sexual reproduction –Germ cells differentiated from soma –Germ cells are younger than the body that produces them! –Selection on germ cells: indirect via the body that produces them Asexual reproduction with asymmetric division –Differential ages

Age Senescent stage Juvenile stage Prime-age stage Example: red deer survival rates

Caulobacter crescentus Ackermann, Stearns and Jenal 2003.

Asexual reproduction via symmetric division (clones) ”Mother” and ”daughter” have the same age! Immortal? No ageing!

Concepts Antagonistic pleiotropy –Genes with a positive effect early in life may have a negative effect late in life (effect of selection reduced with age) Accumulation of mutations –Effect of selection reduce with age Intrinsic vs. extrinsic mortality factors –Intrinsic factors are sensitive to allocation rules –Allocation to the repair of mutations

Variation in life length Invertebrates Mammals Effect of phylogeny

Cole’s paradox ”for an annual species, the absolute gain in intrinsic population growth which could be achieved by changing to a perennial reproductive habit would be exactly equivalent to adding one individual to the average litter size”. Semelparous life history N t+1 = e r N t = B a N t ; e r = B a r = lnB a Iteroparous life history N t+1 = e r N t = B p N t + N t ; e r = B p + 1 r = ln(B p + 1) Given that the two life histories are equal: B a = B p + 1

Given juvenile (P j ) and adult mortality (P a ) Semelparous life history N t+1 = Pj Pj BaNtBaNt Iteroparous life history N t+1 = Pj Pj BpNt BpNt + Pa Pa Nt Nt = Nt Nt (P j Bp Bp + Pa)Pa) Given that the two life histories are equal: Ba Ba = Bp Bp + P a /P j Two important points: Increased P a and reduced P j favours semelparity because that values of juveniles increased relative to adults. Assumption: age at maturity is the same!

Lets introduce variation in age at maturity (Charlesworth 1980): Fitness of an iteroparous and semelparous life history is equal when: B p / B a = 1 - S a /  = N t+1 / N t S a = adult survival Adult survival (S)

Roff 2002 Plants Snails Flatworms

A simple graphical method Adult survival Optimal reproductive effort Lines of equal fitness (isoclines) If we assume a trade off curve between adult survival and reproductive effort:

Adult survival Optimal reproductive effort Lines of equal fitness (isoclines)

Adult survival Optimal reproductive effort Lines of equal fitness (isoclines)

Adult survival Optimal reproductive effort Lines of equal fitness (isoclines) The trade off curve between adult survival and reproductive effort ≈ residual reproductive value Steep early in life Flat late in life Prediction: Increasing reproductive investment with age.

Trichoserus vulpecula Brushtail possum primiparous Middel aged old Reproductive effort P (survival to breed again) Head length/ body mass Isaac and Johnson 2005.

What selects for a long reproductive life Large variation in progeny survival –Mean and variance of progeny variance: –Large variance: geometric mean << arithmetic mean –Small variance: geometric mean ≈ arithmetic mean Bet-hedging

European perch Heibo, Magnhagen and Vøllestad, 2005