lecture 7. sexual selection. costs of sex cost of meiosis cost of producing males cost of courtship...
TRANSCRIPT
Lecture 7. Sexual Selection
Costs of sex
• Cost of meiosis• Cost of producing
males• Cost of courtship and
mating
Benefits of sex• Protection against
mutations (Muller’s ratchet)
• Protection against environmental changes (Raffle hypothesis)
• Protection against biotic fluctuations (Red Queen hypothesis)
”Now here, you see, it takes all the running you can do to keep in the same place.”
The Red Queen hypothesis
Why do male and female gametes differ in size?
Geoffrey Parker et al.:divergent evolutionary selectionfavoured two types of gametes:
small and mobile (sperm)sedentary and packed with nutrients (eggs)
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Darwin (1871, p256):
“We are, however, here concerned only with that kind of selection, which I have called sexual selection. This depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction.”
Sexual selection
1. More individuals are produced than manage to reproduce
2. Individuals differ in their ability to compete with others
for mates or to attract members of the opposite sex
Result: the evolution of traits that enhance reproductive success while decreasing survivorship
What about these
Inrasexual Selection
Members of one sex compete among themselves for access to members of the other sex
Competition before mating
Competition after mating
Competition following conception
Bruce effect in rodents
The pregnancy of a recently inseminated female is terminatedupon exposure to an unfamiliar male
Male infanticide in langur monkeys.
Male infanticide in lions
Explain This ?
Intersexual Selection
Members of one sex (mostly males) ‘advertise’ that they are worthy of an investment.
Members of the other sex (usually females) choose among them.
Sexually selected “ornaments” of males
Darwin argued that sexual selection via female choice was responsiblefor the evolution of male displays and plumage
The widowbird (Euplectes progne),a species the size of a blackbirdthat is endowed with a half-meter long tail
Sexual selection for tail length in long-tailed widowbirds
(Andersson 1982)
Mate-choice copying in the guppy (Poecilia reticulata)
One female’s choice of a mate affects another female’s choice
Male zebra finch
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Fluctuating asymmetry: The extent of asymmetry in bilaterally symmetrical traits
Sailfin Molly (Poecilia velifera)
Normal High Perfect