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University of Toronto Scarborough
Joyce Parga

ANTC23-Lecture 1 1) Understand the process of sexual selection and components 2) Understand how primate, social behavior, and different traits can be adaptive  Adaptive: a trait or behavior functions to increase an individual’s reproductive success relative to other individuals in the population (e.g male-guarding, or sexual jealously in humans) ANTC23- Lecture 2 Introduction to Non-Human Primates  Primate Order -prosimians, monkeys, apes, humans -humans, apes, and monkeys=anthropoids. Prosimians are everything else  Anthropoids -general traits: larger bodied than prosimians, larger relative brain size than prosimians, reduced reliance on smell (visual communication more important)  Lemurs can identify family members based on scent; they don’t have tons of facial expressions -anthropoids are almost all diurnal -have slower life-history than prosimians (take more time to sexually mature, live longer, longer gestation lengths)  Lemurs in their teens are already considered old, and they are only pregnant for about 4 ½ months  Apes -chimps, gorillas, and orangutans=great apes -gibbons and siamangs=lesser apes  Common Chimps (pan troglodytes) -males aggressively dominate females -“alpha” individual in group is always a male -copulation used strictly in a reproductive context -found in multi-male, multi-female groups (just like Pygmy Chimps)  Pygmy Chimps (pan paniscus, bonobo) -relationships between males and females are egalitarian -some groups have an “alpha” female -copulation used in many contexts (lessen tension in a group, in reconciliation, as greetings). Happens b/w 2 females, male/female, or male/male  Gorillas -found in single-male, multi-female and multi-male, or multi-female groups -groups usually have at least 1 silverback male. Silverbacks are usually the oldest, therefore also the dominant  Orangutans (Pongo) -live semi-solitarily (single males and females come together to mate or if food is abundant in an area) -intense male-male competition for female mates -males large in body size compares to females -males have cheek flanges (huge flaps on side of face) that females lack  These traits have been hypothesized as being secondary traits involved with sexual reproduction -forced copulation is a common mating strategy for males  Gibbons & Siamangs (lesser apes) -live in stable male-female pairs (“pair bonded” -once thought to be monogamous but extra-pair copulation occur  Monkeys -New World Monkeys: all are arboreal, all have tails (some prehensile), smaller body than Old World Monkeys, most live in multi-male multi-female groups, a few are pair- bonded  Old World Monkeys -larger bodied than NW monkeys -more terrestrial than NW monkeys -most live in multi-male, multi-female groups. But there are also single-male, multi- female groups  Hamadryas Baboon live in single-male, multi-female groups. The rest are multi- male multi-female  Prosimians -small-bodied, -many are nocturnal (big pupils are an indicator of this) -faster life-history than anthropoids (reach sexual maturity faster, shorter gestation, shorter lifespan)  Lemurs start mating within a year; chimps take years to get ready to mate -Some live in multi-male multi-female groups. Some are solitary, others live in male- female pairs (ruffed lemurs are found in different groups not just family groups) --chemical communication plays a large role in social behavior (e.g. scent marking)  Mating Systems *see figure 3.3 in Dixson (pg. 26) Types: Monogamy: 1 female mates with 1 male exclusively (e.g. owl monkey, titi monkey) Polyandry: 1 female mates with multiple mates, but each male only mates with that one female (marmosets and tamarins) Polygyny: more common mating system in primates. 1 male mates with multiple females but each female only mates with that one male Polygynandry: both males and females mate with multiple individuals of the opposite sex. Also called multi-male multi-female mating system or promiscuous mating system. Extremely common. Dispersed: individuals only come together to mate, and do not live in permanent social groups. You can still have males competing for females. Occurs in many nocturnal prosimians (e.g. aye-aye, galagos, mouse lemurs) ANTC23 Lecture 3 Sexual Selection -mating success: number of copulations achieved -reproductive success: number of viable offspring produced  Sex Differences -female reproductive success is limited by access to resources (food, water, etc) -males have higher potential reproductive rate than females  Females limited by gestation and lactation, males are only limited by number of successful fertilizations Example: humans - females can conceive only 1-2times/yr -males can have hundreds of children across a lifetime -women’s maximum possible reproductive success is much more limited than males  Differences In Reproductive Variability -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 have many offspring, some have little to none  Sexual Selection -definition: a form of natural selection acting on variation in the ability of individuals to compete with others of the same sex and to attract members of the opposite sex 2 Main Components: Intra-Sexual Selection: selection that results from competion between members of the same sex for mates Inter-Sexual Selection: selection that results from mate choice (epigamic selection is another word for mate choice) -possible to have both components  Mate Choice -females are considered to be more selective than males when choosing mates because of the greater parental investment  Sexual Coercion -definition: the show or threat of force that males a female more likely to mate with a male when she is fertile, but at some cost to the female -forced copulation: extreme form of sexual coercion in which an individual is forcibly mated  In orangutans, forced copulation if performed by unflanged and flanged males. Because they are a solitary species, it might be genetically hardwired  Forced copulation can be considered a male mating strategy  Sexual Agression in Humans -one hypothesis: sexual coercion and forced copulation (rape) are human mating strategies -which males are expected to use these strategies?  Males that are unsuccessful in completion for the resources and status needed to attract and reproduce with desirable female  Male Dominance Status -high dominance rank:  Believed to indicate genetic quality (good genes)  Often leads to mating success for males “Priority of Access” Hypothesis: -applies to multi-male, multi-female groups having a male dominance hierarchy -attempts to describe which males gets to mate and in what order by rank -alpha male should have priority of mating with females if female estrus periods don’t overlap (if more than one female is in estrus then other males get to mate) Problems with this Hypothesis: -rank reversals, or a change in the dominance hierarchy -female mate choice for non-dominant males -alternative mate mating strategies (e.g. sneak copulation)  Male Mating Strategies -sneak copulations:  Patas monkey females will sometimes sneak away and mate with extra group males  Japanese macaque females will sneak away from high-ranking mate guarding males to mate with subordinate males  Consortship -close
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