Evolution of mating systems

Created by jsagot 

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Assortative mating

(Hardy‐Weinberg violation) nonrandom mating in which individuals mate preferentially according to phenotype
-Can increase linkage disequilibrium (usually more homozygotes)
-Can reduce effective population size, thus increasing genetic drift and reducing genetic variation

Red Queen hypothesis

each species has to run (evolve) as fast as possible just to stay in place -- because predators, competitors, and parasites also continue to evolve

Muller's Ratchet

Sexual reproduction is so common bc it solves problem of mutational accumulations in generations; sex via recombination produces organisms with small genetic (mutational) load

isogamy

reproduction by the union or fusion of gametes of the same size and structure

anisogamy

reproduction by the union or fusion of two differing gametes (especially differing in size)

4 ways of Sex Determination

sex chromosomes, hormonal signaling, environment, pheromone signaling between individuals

Why not more than 2 sexes?

Hypothesis 1) sperm/eggs are an alternative strategy and any intermediate sized gametes weren't selectively favored
Hypothesis 2) increased number of sexes to mate would increase the cost of sex

2 Reasons for an uneven sex ratio in offspring

1-local mate competition results when a small group of related individuals are mating(siblings for ex:wasps, bees) - more females
2- condition dependent sex allocation results in

monogamy

one female mates with one male

polygamy

mating with more than one individual

polygyny

one male with "many females"

polyandry

one female with "many males"

polygynandry

multiple males and females mate a social group

promiscuity

both males and females mate with whomever is around

Monogamy or polygamy ?

1-if raising offspring takes two=monogamy, if not=polygamy
2-if breeding season is short monogamy guarantees mates
3-sexual conflict
a)males are limited by the number of females, while females are limited by # of offspring
b)males want sole access to mates
c)females want best quality offspring

2 ways to be hermaphroditic

1-simultaneous
2-sequential

Sequential Hermaphrodite

protandrous-"male first" then turn into females later
protogynous-"female first" then turn into males later

protandry favored when . . .

only the largest males get access to females

protogyny favored when . . .

females mate with multiple males and larger females can produce far more offspring than smaller ones

self-fertilization(selfing)

a means of reproductive assurance, favored when growing season is short, mates are scarce, or, in plants where there are few pollinators

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