Sexual Selection (I)

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Sexual Selection (I)
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Costs of sex

• Cost of meiosis
• Cost of producing males
• Cost of courtship and mating

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Benefits of sex

• Protection against mutations (Mullers ratchet)
• Protection against environmental changes (Raffle
  hypothesis)
• Protection against biotic fluctuations (Red Queen
  hypothesis)

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The Red Queen hypothesis
Now here, you see, it takes all the running
you can do to keep in the same place.
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Why do male and female gametes differ in size?

• Geoffrey Parker et al.
• divergent evolutionary selection
• favoured 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.
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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