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L17 - Sexual Selection

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Biology 1001A
Tom Haffie

L17 - Sexual Selection Mutational explanation - despite fitness costs to individual is widespread because it benefits the species by speeding up evolution - vastly decreased risk of extinction - speeds up the rate that helpful mutations are combined into the same genotype - NOT sufficient to explain WHY sex is so widespread - Selection does not favour traits that benefit the group if it comes at the expense of individual fitness - Mutational explanations are unsatisfying Ecological explanations - we need a better explanation - perhaps sexual reproduction results in production of higher quality offspring? Immediate individual advantage to reproducing sexually - Lottery ticket hyp – sex in constant versus unpredictable environments - Benefits the indiv. To reproduce sexually if the environment is changeable. - If environment is not likely to change, fit female should reproduce asexually (rarely the case – unstable environment) - Reproducing asexually in an unstable environment is not favourable - Sexual reproduction: maximize likelihood that SOME offspring will survive in changing environment - Red Queen Hyp * sex is favoured when your environment (natural enemies) is continually evolving * coevolution w/ parasites and other pathogens * coevolutionary arms race w/ organisms that cause disease * greater advantage of reproducing sexually b/c parasites put negative frequency dependence on hosts * sex is advantageous * ex. Freshwater snails Long-term advantages - removing harmful mutations and combining helpful mutations Short term advantages - bet-hedging in a changing environment ( ecological ) - sex is highly advantages in coevolution w/ parasites Which is more important in maintaining sex? - reduced extinction risk may just be a consequence of sex, not an explanation 2 Consequence of Sex: Sexual Selection - depends not on a struggle for existence; but on a struggle between males for possession of females - struggle for few or no offspring - explains sexual dimorphism - explains traits that reduce survival (decrease survivorship – problem for
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