201_W18_12_Primate+Mating+Systems.pdf

28 intrasexual selection in males increased male body

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28 Intrasexual selection in males Increased male body size and canine size are common targets of intrasexual selection Often leads to sexual dimorphism (SD)
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Intrasexual selection in males SD should be most pronounced in groups where males compete most = single-male/multi-female 29
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Reproductive Strategies: Single- male groups A male tries to establish residence in an unrelated group of females, and then restricts access to other males Other males constantly try to take over e.g. baboons, geladas, Hanuman langurs 30
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Reproductive Strategies: Multi-male groups In most primates, females have estrus In multi-male/multi female groups, estrous females can mate with several males in group Less direct competition over access to females Here, intrasexual selection favours increased sperm production – ± sperm competition ² 31
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Repro Strategies: Multi-male groups In multi-male/multi-female groups, dominance hierarchies may also form among males – Determine access to estrous females 32 Dominance hierarchy reflects competitive ability (threats, etc.) Younger males have higher ranks – better physical condition? RS related to age Rank and RS in baboons
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Reproductive Strategies: Pair- bonded males In pair-bonded species (e.g. gibbons), males don’t compete for access to females RS depends more on finding mates, defending territory, and rearing surviving offspring Mate guarding is a common rep. strategy 33 Grooming in white-handed gibbons
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Adaptive strategy for males After group takeovers, males kill dependent offspring Females return to estrus allowing infanticidal male to reproduce more quickly (before they are ousted) Infanticide is costly for females – So expect counter-strategies such as false estrus, female coalitions, spontaneous abortions, male “friendships”, etc. Observations have been made in a large number of primate species, in the wild and in provisioned populations. 34 Reproductive Strategies: Infanticide
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Infan>cide Counterstrategies Concealed ovula>on Regularly sexually recep>ve 35
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