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BIOL 2P92 (117)

Intrasexual Selection

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Ingrid Makus

Intrasexual selection- differential mating success among individuals of one sex due to interactions with members of the same sex (ex. Fighting with each other over the opposite sex); for example, differences in mating success among males due to male-male competition over access to females Intersexual selection- differential mating success among individuals of one sex due to interactions with members of the other sex; for example, variation in mating success among males due to female choosiness ; competition by advertising for their mates by singing, dancing, or showing off bright colours 11.2- Sexual Selection on Males: Competition  Sexual selection by male-male competition often occurs when individual males can monopolize access to females  Males may monopolize females through direct control of the females themselves or through control of some resource important to females, such as feeding territory or nest sites  Male-male competition can also occur for no apparent reason beyond simply impressing females  There are three forms of male-male competition: outright combat, sperm competition, and infanticide Combat  Outright combat is the most obvious form of male-male competition for mates  Intrasexual selection involving male-male combat over access to mates can favour morphological traits including large body size, weaponry, and armour  Male-male combat also selects for tactical cleverness  In iguanas: after sexual interaction, females lay their eggs and go and hide it far away from predators, guards the eggs for a few days, and then abandons it o Therefore parental investment by females consists mostly of producing eggs, and parental investment by males consists entirely of producing ejaculates  Read Example Combat of Iguanas Pg. 408-412 Sperm Competition  Male-male competition does not necessarily stop when copulation is over  The real determinant of a male’s mating success is not whether he copulates, but whether his sperm fertilize eggs
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