Sexual Selection (I)

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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Explain This ?

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