Life History Evolution Flashcards
life history
an individuals patterns of allocation. throughout life, of time & energy to various fundamental activities such as growth, body repair, metabolism, & reproduction
lifetime reproductive success
the number of offspring produced by an individual in their lifetime
trade offs
inescapable compromises between traits that limit their evolution
life history examples
- some species mature early & reproduce quickly, others mature late & reproduce slowly
- fundamental trade-off between offspring size & number
life history examples: some species mature early & reproduce quickly, others mature late & reproduce slowly
- female deer mice mature at ~7 weeks & have 3-4 litters of pups each year
- female bear mature at 4-5 years & have pups every 2 years
- some trout reproduce multiple times, but salmon reproduce once & die
life history examples: fundamental trade-off between offspring size & number
- the oyster releases 10-50 million eggs in a single sperm, each very tiny
- the clam broods <100 eggs, each very large
life history in blue footed boobies
- in males, feet range from dull blue to bright green
- females prefer bright green feet
- maintaining bright feet gets harder as the birds age
- males that take a year off from reproduction have brighter feet
the ideal organism
- mature at birth
- continuously producing a large amount or large offspring
- live forever
Brown Kiwi
- females weight ~6 lb
- 1 lb egg
- only 1 egg is laid at a time
- high quality
Sea Urchins
- females take a few years to get to a reproductive age
- lay 100,000-200,000 eggs at one time
- all very tiny with very small chance of success
Thrip egg mites
- mites that eats the eggs of a small plant eating insect called a thrip
- females mate with their brother in womb, then eat their way out of mom
- born mature, live 4 days
energy allocation in the Virginia Opossum trade offs
- a different female that begins reproducing sooner will be smaller & have smaller litters, but may be likely to actually reproduce
- a female that allocates more to tissue repair will have less to give to reproduction, but may live longer
energy allocation in sand crickets
- short winged females devote more of their energy to reproduction & will produce sooner, but can’t disperse well
- long winged females devoted more energy to flight muscles, but reproduce later in life
senescence ________ an individuals fitness
reduces
senescence
a decline with age in reproductive performance, physiological function, or probability of survival
longevity evolves: 2007
Eskimo hunters killed a bowhead whale & found in its flesh a kind of harpoon that was used only around 1890
longevity evolves: 1999
growth patterns in the teeth of a bowhead whale suggests that it is 211 years old
The Evolutionary Theory of Aging
- mutation accumulation hypothesis
- 97% of all offspring in the population are produced by individuals ages 13 or less
- selection on late acting mutations is weak
- an individual with a mutation that kills them at age 2 has 0 fitness
- selection on early acting mutations is strong
mutation accumulation hypothesis
mutations that impact fitness late in life are under weak selection
if inbreeding depression is caused by deleterious alleles and late-acting deleterious alleles are at higher frequency under mutation-selection balance because selection is weaker on deleterious alleles, THEN…
severity of inbreeding depression should increase with age
houseflies aging
in houseflies that are allowed to reproduce for 5 days only, longevity quickly declines because late-acting mutations accumulate
why is the relationship the same for large & small populations?
given neutral evolution, the rate of substitution is equal to the mutation rate: K = u
in a diploid population, the number of new mutations per generation at a locus =
2NeV
2NeV variables
- Ne = number of copies of a gene
- V = mutation rate of new selectively neutral mutations per gene copy per generation
for a neutral mutation, the probability of fixation =
1/2Ne
the rate of substitution at a locus K:
2NeV * 1/2Ne = V substitution/generation
pleiotropy
when a single gene influence multiple traits
antagonistic pleiotropy
when the alleles at a locus have fitness benefits & costs
the antagonistic pleiotropy hypothesis for senescence
mutations conferring fitness benefits early in life & fitness costs late in life will be under positive selection when the benefits outweight the costs
is pleiotropy common or uncommon?
very common
frizzle mutation in chickens
feathers curl outward instead of lying flat against the body
other effects of the frizzle mutation in chickens
- higher metabolic rate
- higher body temp
- greater digestive capacity
- lay fewer eggs
- morphological changes in the heart, kidney, and spleen
predictions of the evolutionary theory of aging
populations with lower rates of ecological mortality should evolve delayed
antagonistic pleiotropy hypothesis
mutations conferring fitness benefits early in life & fitness costs later in life can be advantageous
what is predicted by both theories of aging?
- mutation accumulation hypothesis
- antagonistic pleiotropy
antagonistic pleiotropy
lower mortality means more individual will live long enough to experience late-life costs, so that natural selection on these mutations is stronger
the antagonistic pleiotropy hypothesis for senescence
mutations conferring fitness benefits early in life & fitness costs late in life will be under positive selection when the benefits outweigh the costs
mutation accumulation hypothesis
- lower mortality means more individuals will live long enough to experience the deleterious effects of late-life
- this increases the effectiveness of natural selection & holds deleterious alleles in mutation/selection balance at lower frequency
antagonistic pleiotropy in the Virginia Possum
- on an island = lower mortality
- on the mainland = higher mortality
connective tissue physiology
- collagen fibers from cross links between protein molecules as we age, making out tendons stiffer
- the amount of cross-linking can be measured by how hard it is to break the collagen fibers in tendons
how many offspring in brown kiwi?
- females weigh 6 lbs, lay a 1 lb egg
- 1 large eggs
connective tissue senescence
collagen fibers in the tail take longer to break in older individuals, but it is worse on the mainland
how many offspring in sea urchins?
- females take a few years to get to reproductive age
- lay 100,000-20,000 tiny eggs
fundamental trade-off between size & number of offspring
more offspring = smaller size
less offspring = large size
parental fitness
number of offspring times expected survival
study on Chinook Salmon
- a * b = c
- the optimal egg size in the hatchery is smaller than in nature & egg mass has evolved a smaller size in the hatchery
- rivers that receive lots of hatchery fry have evolved smaller eggs as a consequence of gene flow from the hatchery fish
Lack’s (1947) hypothesis
natural selection will favor the clutch size that maximizes the number of surviving offspring
how does clutch size affect the probability of survival?
larger clutch size, smaller probability of survival
Collard Flycatchers in Sweden
- daughters from larger clutches have smaller clutches
- trade-off between quantity & quality
- the optimal clutch smaller size than the size that maximizes hatchling survival for any one year
