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

3. fecundity, mx
age, x

4. 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?

5. 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?

6. 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?

7. 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?

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

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

12. 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

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

14. 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

15. 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

16. 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

17. 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

19. 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

22. 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 Evolution 41:1370
stream with waterfall: above: no guppies, Rivulus
below: guppies, Crenicichla
introduce 100 fish (incl. many gravid &&) above waterfall,
what happen??

23. 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)

25. 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

26. 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 ?

27. Reznick et al 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

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

30. 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

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

35. 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

36. Stearns 1990

37. 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