a201-11f-17-MatingSexualSelection

Selection under these complicated variable

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- selection under these complicated, variable circumstances might favor flexible behavior and complex cognition - might also maintain more behavioral and physical variation in the species, which makes them able to evolve more quickly in response to new environmental pressures, diseases, etc. - multi-male, multi-female groups:
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Intro to Biological Anthro F 2011 / Owen: Sexual selection p. 7 - two kinds of male-male competition: - 1. between resident males and bachelor males for access to females - bachelor males hang around the edges of the group, trying to mate with the females - or bachelor males charge right into the group and confront the resident males - 2. between resident males within the group for access to females - males try to drive other males away from females - interrupt mating - or males may establish dominance relationships through spontaneous confrontations not directly related to access to females - these establish which males are dominant over which others - confrontations vary from stylized threats, with one male backing down, to real fights - the vanquished male typically acknowledges this by a stereotypical gesture of submission - sometimes this is a facial expression, or a posture like resting on the “elbows” of the forelimbs in order to lower the head, or a particular kind of sound - selection favors these signaling behaviors because those that use them are less likely to get beat up in fights - they survive to try again later - in many cases, the dominance relationships are fairly stable, and a dominance hierarchy is formed - similar to the dominance hierarchies among females - which give the dominant females better access to resources - dominant males do tend to have higher reproductive success - although there are interesting exceptions - males may form social alliances to get access to females - a high-dominance male will form a “ consortship ” with a female in estrus - he stays with her, grooms her, mates with her, and keeps other males away - this behavior assures that the offspring is his - two less-dominant males may team up as a “ coalition ” to challenge the consorting male - they can often succeed in driving off the more dominant male - and one of the allies becomes the female's consort - Infanticide - in single-male, multi-female groups - when a new resident male drives off the old one, the new male will sometimes kill many of the infants - this has now been observed in numerous species - Hanuman langurs (generally single-male) - Red howler monkeys (both single-male and multi-male) - gorillas (generally single-male) - the females who have lost their infants stop lactating and become receptive quickly - so the male can quickly father numerous offspring - males that do this leave more of their alleles in the next generation, so selection favors it
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Intro to Biological Anthro F 2011 / Owen: Sexual selection p. 8 - especially important in single-male species, where the male may not have long before another male drives him away and takes over - this makes the most obvious sense in single-male groups, but it is now clear that
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