Sexual Selection & Secondary Characters. Potential for Sexual Selection: Ratio Variance in Reproductive Success, Lesser PI Sex / Greater PI Sex Monogamy vs Polygyny (Polyandry). Sexual Selection & Secondary Characters.
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Potential for Sexual Selection:
Ratio Variance in Reproductive Success, Lesser PI Sex / Greater PI Sex
Monogamy vs Polygyny (Polyandry)
Same pattern, 4 of 5 years studied
Males disperse from natal colony;
Females philopatric: male-male competition, access to coterie
Female choice: “Ranking adult male” (RAM) in multi-male coteries
V[Male Rep Success] >
V[Female Rep Success]
Sexual Selection More Intense in Males:
Secondary Sexual Characters in Males
Females: Likely Choose Males with Greater PI, Higher Quality Resources, …
But when Male PI lower
Bright Colors, Ornaments,
Elaborate Displays of Males Common
Sexual Selection: Advance Mating Success & Enhance Fitness, Despite Cost
Trinidad guppy (Poecilia reticulata): dichromatism, males brightly colored
Females prefer brighter males as mates,
Brighter males suffer more predation.
Intense predation (cost); male coloration reduced
“Fits;” but why do females prefer brighter males?
R.A. Fisher: runaway process of sexual selection
IF secondary sexual characteristic M expressed in one sex genetically correlated with preference for this trait in the other sex, mate choice for M also selects for strong preference.
Self-reinforcing (runaway) until another force balances sexual selection.
One Allele: bright color in male genome
preference for bright color in female genome
Fisher’s “genetic correlation”
“Sexy Son” Hypothesis:
Given Female Preference,
Female Chooses Male Genes Likely to Render Her Sons Attractive
Doesn’t Answer Question ?
“Good Genes” Hypothesis:
Females Choose Mates with Genes
Increasing Mean Fitness of her Offspring
Circular? Correlates of good genes?