cost of males, cost of meiosis, gonads are expensive to reproduce and maintain, mating is risky and costly, often involving elaborate behaviors
leads to greater contributions to subsequent generations
benefits of sex
novel gene combinations are created, prevents Mullers ratchet
Red Queen Hypothesis
need to create new gene arrangements to combat pathogen evolution
mutations will accumulate in asexual lineages because there is no recombination
gametes of unequal size
gametes of equal size
evolution of anisogamy
selection pressures to produce bigger gametes, more gametes.
conflict of interest between sexes
differ in amount of investment, bigger gametes (more parental investment), more gametes (less parental investment
male fitness increases with number of mating events, female fitness does not change with mating events, thus female (eggs) are a limiting resource- so males will compete for mating opportunities
investment on offspring that increase their chance of survival at the cost of future offspring
influences the degree to which a female can alter the sex ratio of her offspring
sex chromosomes are different for each sex (Female; XX , Male; XY)
type of sex-determination system, sex is determined by the number of chromosomes an individual receives. Haploid males develop from unfertilized eggs, diploid females develop from fertilized eggs.
environmental sex determination
temperature of incubation influences sex determination (mainly reptiles)
social sex determination
many fish can undergo sex changes. Ex CA sheephead, all born female, dominant female changes into males when a male disappears
individual sex allocation depends on condition (if mom is in good condition they give more parental care to sons than daughters b/c dominant sons can sire more offspring, if in poor condition should produce more daughters.
local mate competition
mating occurs near hatching site (brothers compete for mating), produce few sons.
local resource competition
offspring that stay near their birth site may compete with their parents for resources (produce more dispersing sex)
local resource enhancement
in some species offspring of one sex remain at the nest to help parent raise their species.