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Joyce Parga

ANTC23 L3 Introduction to Sexual Selection - Mating success: number of copulations achieved - Reproductive success (RS): number of viable offspring produced - One might have high number of having sex (mating success) but if female does not get pregnant or their offspring dies very young, his reproductive success is very low. So mating success does not equal reproductive success. Sex differences in the limiting factors for reproduction - Male reproductive success is limited by access to mates (the number of females he can inseminate) o How many babies the flanged orangutan has is limited to the female access - Female reproductive success is limited by access to resources (food, water, etc.) o It is not hard for her to find males but she needs to stay healthy for pregnancy - Males have higher potential rates than females - Males are only limited by the number of successful fetilization - Females are limited by gestation (pregnancy) and lactation - Example: Duggar family o Females can conceive only 1-2 times per year o Males can have hundreds of children across lifetime o Big difference in potential in reproductive success o Women’s maximum possible RS is much more limited than men’s. Differences in reproductive variability within each sex - Males show greater variability in RS than females - Males can show high reproductive skew (the unequal partitioning of reproductive success among individuals in a population) - Some males sire MANY offspring, while others sire NONE. o i.e. ringtailed lemurs – flat ears mean submissiveness. In low reproductive skew, there is equal number of babies produced by males. In high skew population, the opposite. Sexual selection - A form of natural selection acting on variation in the ability of individuals to compete with others of their own sex and to attract members of the opposite sex - 2 main components o Intra-sexual selection  Males fighting each other, and female fighting each other o Inter-sexual selection Intra-sexual selection - Selection that results from competition between members of the same sex for mates o Male-male or female-female competition o i.e. If they physically fight, then the bigger muscles and body size will be passed down more than the guy who lost. If this happens over and over again, this causes in male weaponry, such as chimp canine or antlers. It is selection process that helps them with sexual selection o i.e. Sperm competition: ramped in baboons, creating large testicle size. So it doesn’t have to be physical competition all the time but you can just have good sperm Inter sexual selection - Selection that results from mate choice - i.e. Say males have certain traits that females like. If females keep selecting these traits over time and if these males have more babies, you see the shift in the physical appearance of these males. o Epigamic selection: mate choice Inter-sexual selection (mate choice) - Females are considered to be more selective than males when choosing mates because of their greater parental investment - i.e. Female vervet monkey has to be pregnant and lactate, so if she makes a bad choice and mates with low ranking male with bad health, she will waste all this time raising the baby that will die. Sexual coercion - The show (or threat) of force that makes a female more likely to mate with a male when she is fertile, at some cost to the female o Male hamadryas baboon neck-biting a female. i.e. punishing her for going too far away from him. It is a cost to her (hurts her, gets infected, etc.) If she gets bitten, she is more likely to stay around her o Male gorilla showing aggression towards a female. Forced copulation - An extreme form of sexual coercion in which an individual is forcibly mated. o In orangutans, forced copulation is performed by both unflanged and flanged males o Can be considered a male mating strategy - Other species in which forced copulation is observed o Patas monkey o Spider monkey o Bonner macaque - Prof’s observation: a female who is not socially dominant yet but is physically sexually mature, a male wouldn’t get off of her when she presented herself. It was not forced copulation but it could be called forced coercion. Sexual aggression in humans - One hypothesis: sexual coercion and forced copulation (“rape”) are human male mating strategies - Which males are expected to use this strategy? Men unsuccessful in competition for the resourced an status needed to attract and reproduce with desirable females (evolutionary psychologists) Male dominance status - High dominance rank o Believed to indicate genetic quality (“good genes”) o Often leads to mating success for males o i.e. Male chimpanzees “Priority of access” hypothesis - Applies to multi-male, multi-female groups having a male dominance hierarchy - Attempts to describe which males get to mate, and in what order - Alpha male should have priority of mating with females if male estrus periods don’t overlap. o
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