What is the age-specific pattern of reproduction? age, x fecundity, mx age, x fecundity, mx Iteroparous Semelparous

fecundity, mx age, x

What is the effect of a lethal mutation at a particular age? Pr(survival), lx age, x fecundity, mx age, x What is the effect of a lethal mutation at a particular age?

What is the effect of a lethal mutation at a particular age? Pr(survival), lx age, x fecundity, mx age, x What is the effect of a lethal mutation at a particular age?

What is the effect of a lethal mutation at a particular age? Pr(survival), lx age, x fecundity, mx age, x What is the effect of a lethal mutation at a particular age?

What is the effect of a lethal mutation at a particular age? Pr(survival), lx age, x fecundity, mx age, x What is the effect of a lethal mutation at a particular age?

Reproductive Value fecundity, mx Pr(survival), lx age, x age, x age, x reproductive value, Vx Reproductive Value Expectation of future offspring

Why do organisms live as long as they do? Why do organisms age? Evolution of Senescence Mutation Accumulation Antagonistic Pleiotropy

Mutation Accumulation age, x reproductive value, Vx effect of deleterious mutations on fitness depends on the age at which they are expressed weight by Vx age, x frequency of mutations Mutations accumulate later in life because little detrimental effect on fitness Selection on interacting loci to shift time of expression

Antagonistic Pleiotropy Trade-offs Between Early- and Late- Age Effects age, x fecundity survival

onset of mutation survival reproduction effect on fitness --- negative --- positive --- negative --- positive positive negative trade-off favored because of effects on fitness no pleiotropy no antagonism

Best is to trade lower later survival for earlier reproduction age, x fecundity survival Increased Survival, but Later Reproduction Decreased Survival, but Earlier Reproduction Best is to trade lower later survival for earlier reproduction

Evidence for Antagonistic Pleiotropy in Drosophila Rose and Charlesworth 1984 Genetics select for increased early (day 1-5) or late (day 21-25) fecundity did not select directly on lifespan

and significantly higher late oviposition than lines selected Lines selected for late fecundity had significantly less early oviposition and significantly higher late oviposition than lines selected for early fecundity Rose 1984

integration and constraint ---> trade-offs age at maturity, lifespan growth rate, size at maturity clutch size, age at maturity offspring size, clutch size clutch size, number of clutches lifespan, number of clutches effectiveness of selection is influenced by age-specific mortality and reproduction (evolution of senescence) patterns of age-specific mortality and reproduction also evolve

Experimental tests of life history evolution guppies, Poecilia reticulata: neotropical, live in streams life history shaped by predation: Crenicichla (pike) eat large, sexually mature guppies ---> early age of maturity; greater reproductive effort; more, smaller offspring Rivulus (killifish) eat small, juvenile size classes ---> delayed maturity; fewer, large young; less reproductive effort Reznick and Bryga 1987 Evolution 41:1370 stream with waterfall: above: no guppies, Rivulus below: guppies, Crenicichla introduce 100 fish (incl. many gravid &&) above waterfall, what happen??

Introduced population will change in life history because of differences in selection by predator (Rivulus) Predictions adult size intro (R) > control (C) age of 1st reproduction intro (R) > control (C) reproductive effort intro (R) < control (C) fecundity (developing #offspring) intro (R) < control (C) offspring size intro (R) > control (C)

Introduced population will change in life history because of differences in selection by predator (Rivulus) Predictions: adult size intro (R) > control (C) T males, females age of 1st reproduction intro (R) > control (C) T males only reproductive effort intro (R) < control (C) NS fecundity (developing intro (R) < control (C) T #offspring) offspring size intro (R) > control (C) T

introduction experiment is N = 1 !! alternate approach ---> convergent evolution compare independent sets of populations with similar selection pressures (types of predators) do life history traits change in parallel ?

Reznick et al 1996 Amer. Nat. 147:319, 339 south slope: high predation (Crenicichla); low predation (Rivulus) SA freshwater origin of predators (cichlids, characins) north slope: high predation (Eleotris); low predation (Rivulus/ Macrobrachium) -- marine origin of predators

high: more but smaller, offspring; smaller adult size; greater reproductive effort low: few, large offspring; larger adults; lower reproductive effort

Comparsion of north slope and south slope populations -- both show predicted changes in LH under high vs low predation regimes Laboratory rearing study in a common environment to measure the extent to which differences between high and low predation populations have a genetic basis

North slope populations are all significant; South slope only for the first clutch

Causes of convergence design constraints -- integrated complex of traits e.g., larger offspring--->larger female body size --->delayed maturity; --->reduced number of offspring; --->longer development independent evolutionary response to environmental similarity -- individual optimization of traits genetic correlations positive for age and size at maturity but, lack of negative for offspring number and offspring size little evidence for tight integration

Stearns 1990

Life history traits are those which are concerned with “decisions” about allocation of resources to maintenance, growth or reproduction Life history traits often show trade-offs or correlations -- e.g., increased size of offspring may be related to a decreased number of offspring -- these trade-offs represent constraints on the evolution of life history characters Guppies provide an example where changing predation in a population changes selection pressures on the timing of reproduction, reproductive effort and adult size Senescence evolves because selection on deleterious mutations changes as a function of age; mutations that enhance early reproduction (even to the detriment of lifespan) will be favored by selection