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Lecture 17

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Biology 1001A

Lecture 17  Mutational explanation for sex:  o Sexual recombination benefits the species by speeding up evolution o  discarding harmful mutations  combining beneficial mutations o ... this decreases the likelihood of extinction o Selection does not favour traits that benefit long-term persistence of 'the group' at the expense of immediate individuals o  selection is very strong on individuals than groups  Ecological Explanations:  o in a changing environment, sex benefits individuals o Lottery ticket hypothesis: sex in constant versus unpredictable environments o  if environment does not change, she can reproduce asexually, more copies of herself   asexual is favoured  if environment changes, reproducing asexually, is very bad because if the environment selects against the organism, it will die out  but if organism reproduce sexually, there's mutation and the offspring might be better adapted to the environment and survive to reproduce again o Red Queen hypothesis: sex is favoured when your environment (natural enemies) is continually evolving o  parasites are constantly evolving and parasites generate a selection against one without the defence, thus sex can produce parasite resistance alleles so that the individual are parasites free  sex is more advantages, more favoured  Sex is costly and inefficient... but phenomenally successful  o long-term advantages o  removing harmful mutations, and combining helpful mutations o short-term advantages o  bet-hedging in a changing environment  ecological explanation (more important) o which is more important in maintaining sex? o  reduced extinction risk may be just a consequence of sex, not an explanation  Another consequence of sex: sexual selection  o Darwin explanation of sexual selection: result is not death, the result is few or no offspring o explains sexually dimorphism o  both sex doesn't have the same selection pressure o explains traits that reduce survival o  when the organism calls out, or one that looks very distinctive are more easily getting caught and die  Intrasexual or intersexual selection?  o intrasexual selection: o  within sex  within sex, they compete with each other, normally between male-male competition o Intersexual selection: o  between sex  normally females pick males, males do not fight each other  The d
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