201_W18_12_Primate+Mating+Systems.pdf

J b silk et al science 20033021231 1234 20

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J B Silk et al. Science 2003;302:1231-1234
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20 Reproductive Strategies Females Females produce few offspring, invest heavily in each, and can raise them (largely) without males Limiting factor that causes competition and influences the RS of females = access to food Males Males less constrained by food, seldom invest in offspring, hence can potentially mate with many females Limiting factor that causes competition and influences the RS of males = access to mates
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All about access to mates Traits that increase success in competition for mates evolve through a special form of selection: 21 Male Reproductive Strategies Sexual Selection
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22 Sexual Selection Originally proposed by Darwin Special category of natural selection Accounts for features with no obvious survival function ( secondary sexual characteristics) Helps explain traits that seem maladaptive in terms of natural selection (e.g. costly)
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Natural vs. Sexual Selection Natural Selec-on Sexual Selec-on Favours phenotypes related to survival/reproduc>on, e.g. predator avoidance, resource acquisi>on... Favours phenotypes that increase success in compe>>on for mates Affects both sexes Affects one sex more strongly, the one whose access to mates is limited 23
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24 Components of Sexual Selection Intrasexual Selection – Competition within the sex(es) – Usually stronger among males – Common in primates Intersexual Selection – Mate choice – Usually stronger in females – Common in birds, ?primates
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25 Intersexual Selection: What do females want? Females have high parental investment Also reproduce slowly Low reproductive potential Should mate with ± quality ² mates – Do not want to waste rare reproductive opportunities on unhealthy males or those that might produce less competitive offspring
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Intersexual Selec>on Females can choose males that: – Will increase their fitness Defend resources, infanticide protection – Show good “genetic quality” Will produce more fit offspring Measured by condition, and costly traits Text suggests that intersexual selection not important in primates (female choice limited) But may be more common via cryptic female choice (female sperm storage) 26
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27 Intrasexual selection in males Most basic form of male-male competition is to fight and drive other males away Winners have advantage in mating opportunities = higher RS Intrasexual selection favours traits that enable males to be effective fighters
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