life history characteristics. organisms face fundamental trade-offs in their use of energy and time...

Life history characteristics

Organisms face fundamental trade-offs in their use of energy and time

Changes in life history are caused by changes in the allocation of energy

Life history parameters

Number & size of offspring

Age distribution of reproduction

Life span

Life span

tuna-many small eggs-grow quickly, reproduce young-reproduce daily

dogshark-few large eggs-grow slowly, reproduce after 25 years-reproduce every few years

overlapping generations

discrete generations



Life span

Differences in these parameters affect growth rate (fitness)

t = time (days or years)

x = age of an individual (days or years)

lx = proportion of newly laid eggs that survive to age x

mx = expected # of offspring (fecundity)

a = age at first reproduction

z = age at last reproduction

r = growth in population size per female per unit time


increased lx will increase r

increased mx will increase r

offspring produced earlier contribute more to population growth

earlier reproduction begins, greater r

Life history parameter conclusions

Characteristics that would maximize r (fitness):

higher survival through reproductive ages

higher fecundity at each reproductive age

higher fecundity especially early in life

longer reproductive lifespan

earlier age of first reproductive

Life history parameter characteristics

Constraints

phylogenetic

genetic

physiological

Trouble with tribbles




Life span

Lack’s hypothesis

selection will favor the clutch size that produces the most surviving offspring

assumes no trade-off between a parent’s reproductive effort 1 year and its survival or reproductive performance in future years

Lack’s hypothesis

Lack’s hypothesis

assumes only effect of clutch size on offspring is in determining whether the offspring survive

Lack’s hypothesis

selection will favor the clutch size that produces the most surviving offspring

Assumptions:

assumes no trade-off between a parent’s reproductive effort 1 year and its survival or reproductive performance in future years

assumes only effect of clutch size on offspring is in determining whether the offspring survive

Lack’s hypothesis

Organisms face a trade-off between making many low-quality offspring or a few high-quality offspring

fish insects

Size & number trade off

Optimum size & number compromise

Selection on parents favors a compromise between the quality and quantity of offspring, but selection on individual offspring favors high quality




Life span

In populations where mortality rates are high, individuals tend to breed earlier in life

However, a trade-off exists between reproductive effort early in life and reproductive success late in life




Life span

Semelparity & iteroparity

Semelparity-population growth rate is high-juvenile survival is high-adult survival is low

Iteroparity-population growth rate is low-juvenile survival is low-adult survival is high

semelparitysingle reproductive eventPacific salmon

iteroparitymultiple reproductive eventsAtlantic salmon

Male reproductive success

alternative mating tacticssneaker males

sequential hermaphroditismprotandryprotogeny

protandry

protogeny

Sequential hermaphroditism

Sequential hermaphroditism

protandryprotogenyno change

When mates are not monogamous, the life history strategy that is optimal for one sex may be suboptimal for the other

Aging – late life decline in an individual’s fertility and probability of survival

Why does aging persist?

Rate of living theory- accumulation of irreparable damage to tissue

Evolutionary theory- failure of organisms to completely repair damage

Aging

Rate of living theory- accumulation of irreparable damage to tissue

Aging

Aging

telomerase

Evolutionary theory- failure of organisms to completely repair damage

-deleterious mutations

-trade-offs between repair and reproduction

Aging

Lifetime reproductive success: 2.419

Aging

Wildtype: first reproduction: 3, death: 16


Aging

Mutation: first reproduction: 3, death: 14


Aging

Mutation: first reproduction: 2, death: 10

Because natural selection is weaker late in life, alleles that enhance early-life reproduction may be favored even if they also hasten death

Also, alleles that cause aging are only mildly deleterious

Aging

life history characteristics. organisms face fundamental trade-offs in their use of energy and time...

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