Sexual Selection

Sexual Reproduction & Sexual Selection

1. Cost and Benefits of sex: Why does sex exist?

2. Anisogamy and the Bateman Principle

3. Sexual Selection

Cost and Benefits of Sex

• sexual behaviour exist, the benefits must outweigh the costs

• some animals reproduce asexually → parthenogenesis

• sex is expensive

Parthenogenesis

Partheno = virgin, Genesis = birth

Sex is expensive

• cost of meiosis

• cost of producing males → 50/50 chance they survive

• cost of courtship and mating → energy to find/secure a mate, risk of injury

Benefit of Sexual Reproduction

• faster evolution

• harmful mutations can be edited out of the pop.

• sexual reproduction allows species to keep up with predators, viruses, and parasites

Muller’s racket

• mutation pile up in asexual pops.

• Asexual reproductive keeps them in the pop. increasing mutations

Sexual Selection

Divided into intersexual selection and intrasexual selection

Male and Female investment into reproduction

• female success is limited by egg production; male success is limited by access to mates

• females invest more; eggs, caring for young, they are the choosy sex

Anisogamy

• Isogamy → m and f gametes are similar size

• anisogamy → m and f gametes are not same size

  • sperm numerous, small, motile, cheap

  • eggs few, large, senile, costly

Bateman Principle

• male reproductive success (fitness) is determined by