What is the age-specific pattern of reproduction?

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What is the age-specific pattern of reproduction?
Iteroparous
Semelparous
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What is the effect of a lethal mutation at a
particular age?
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What is the effect of a lethal mutation at a
particular age?
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What is the effect of a lethal mutation at a
particular age?
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Reproductive Value
Expectation of future offspring
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Why do organisms live as long as they do? Why
do organisms age?
Evolution of Senescence Mutation
Accumulation Antagonistic Pleiotropy
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Mutation Accumulation
effect of deleterious mutations on fitness
depends on the age at which they are
expressed weight by Vx
Mutations accumulate later in life because
little detrimental effect on fitness Selection
on interacting loci to shift time of expression
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Antagonistic Pleiotropy Trade-offs Between
Early- and Late- Age Effects
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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
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Increased Survival, but Later Reproduction
Decreased Survival, but Earlier Reproduction
Best is to trade lower later survival for earlier
reproduction
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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
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Lines selected for late fecundity had
significantly less early oviposition and
significantly higher late oviposition than lines
selected for early fecundity
Rose 1984
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integration and constraint ---gt
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
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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 ---gt early age of
maturity greater reproductive effort more,
smaller offspring Rivulus (killifish) eat small,
juvenile size classes ---gt delayed
maturity fewer, large young less
reproductive effort Reznick and Bryga 1987
Evolution 411370 stream with waterfall
above no guppies, Rivulus below guppies,
Crenicichla introduce 100 fish (incl. many
gravid ) above waterfall, what happen??
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Introduced population will change in life history
because of differences in selection by predator
(Rivulus) Predictions adult size intro
(R) gt control (C) age of 1st
reproduction intro (R) gt control (C)
reproductive effort intro (R) lt control (C)
fecundity (developing offspring) intro (R) lt
control (C) offspring size intro (R) gt
control (C)
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Introduced population will change in life history
because of differences in selection by predator
(Rivulus) Predictions adult size intro
(R) gt control (C) T males, females age of
1st reproduction intro (R) gt control (C)
T males only reproductive effort intro
(R) lt control (C) NS fecundity (developing
intro (R) lt control (C) T offspring)
offspring size intro (R) gt control (C) T
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introduction experiment is N 1 !! alternate
approach ---gt convergent evolution compare
independent sets of populations with
similar selection pressures (types of
predators) do life history traits change in
parallel ?
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Reznick et al 1996 Amer. Nat. 147319, 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
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high more but smaller, offspring smaller
adult size greater reproductive effort low
few, large offspring larger adults lower
reproductive effort
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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
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North slope populations are all
significant South slope only for the first
clutch
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Causes of convergence design constraints --
integrated complex of traits e.g., larger
offspring---gtlarger female body size
---gtdelayed maturity ---gtreduced number of
offspring ---gtlonger development independent
evolutionary response to environmental similarit
y -- 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
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Stearns 1990
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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