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University of Toronto Scarborough
Joyce Parga

Females: - Receptivity: a female’s willingness to allow a male to copulate - Proceptivity: female behaviour that functions to initiate and maintain sexual interaction with a male o Sexual solicitation (seduction) o Takes a form of a “sexual presentation” Male: i.e. Common chimp/bonobo sometimes display an erection (inviting to mate) Estrus: A period of heightened sexual activity/receptivity by female mammals, usually around ovulation (discharge of an ovum/egg from ovary) Periovulatory Period (POP): A period during and immediately preceding/following ovulation. - Prosimians: reproduction is strongly controlled by hormones - Anthropoids: mating is freed from hormonal control, can mate outside of POP (“Non-conceptive mating”) o Can mate when pregnant/not ovulating Sexual skin – 2 types - Sexual swellings in OW and apes - Facial coloration in some OW Sexual swellings: Estrogen-dependent swelling of skin around the vaginal area during the POP - Common chimps and bonobo - Macaques - Baboons o Some peri-vaginal “pinkening” - Hypotheses: 1. Signals optimal time for mating (maximal fertility) 2. Reliable indicator of female quality 3. Long-range mate attraction: attract males from outside the group 4. Stimulate male-male competition (by sexually exciting males) so that females can mate with the “best” male Copulatory calls: Sometimes during copulation, sometimes at point of ejaculation or orgasm - Coordinates copulatory movements of male and female - Cause competition between males by alerting others (to the mating pair) Long calls (“loud calls”) - In orangutans: o By flanged males o To advertise their presence to females o Male-male competition - In Ring-tailed lemur o By males, mostly during the mating season o Honest advertisement of quality to females o Male-male competition Primate orgasm - Behavioural evidence (Strongest evidence in macaques and apes) o “Clutching” o Facial expressions o Certain vocalizations - Physiological evidence o Respiration and heart rate increase o Uterine and vaginal muscle contractions - Adaptive functions o Stimulate ejaculation o Encourage females to seek more mating partners - causing sperm competition o Muscle contractions stimulate sperm transport o Cryptic female choice (mate discrimination during or after copulation) Post-ejaculatory refractory period: following ejaculation, males cannot immediately mate and ejaculate again Masturbation  Both sexes (even when sexual partners are present) - Humans, apes, OW, and a few NW - Adaptive functions: o Not “wasting” sperm, but to “flush out” old low quality sperm  speculative hypothesis at present Movie – The Uncommon Chimpanzee - Captive bonobos at the San Diego Wild Animal Park in California - Some of the sexual “signals” and behaviors we talked about today will be in the film Sexual dimorphism: morphological differences between males and females in body size and shape Sexual monomorhism: sexes are the same size, color, etc. Sexual dichromatism: color 2 types of competition - Contest competition: when a resource can be monopolized by a single individual or group and can be fought over o Size and strength is an advantage  adaptive and selected for o i.e. Hanuman langurs - Scramble competition: when a resource is exploited by the individual that arrives and uses it first o Small nocturnal prosimians that don’t live in social groups o It can become a contest competition o i.e. Gelada baboons, aye-aye, Howler monkey, gorilla Sexual dimorphism (canine&body size) associated with: - Polygyny i.e. gelada baboon, Hamadryas baboon - Polygynandrous species sometimes have sexual dimorphism (with larger males) i.e. common chimps - Monogamous species are usually sexually monomorphic in body size. i.e. titi monkey Sexual dimorphism & Taxonomic groups - Most apes: sexually dimorphic in body size, with larger males o Except for gibbons and siamangs - sexual dichromatism but pretty much the same size. - Many OW: sexually dimorphic in body size with larger males - Many NW & prosimians: NOT sexually dimorphic in body size o Exception: in some nocturnal prosimians with dispersed mating systems, males are larger than females. i.e. galagos Secondary sexual characteristics: external traits that help distinguish the sex of an individual, but are not direct involved in reproduction o i.e. flanges and throat sac (laryngeal sac) of orangutan male - Testosterone-mediated traits o Proboscis monkey - nose o Hamadryas baboon - cape o Gelada baboon - cape - If no obvious function in male-male aggressive competition, these affect female mate choice o Male mandrill o Male uakari (bulges on the forehead, temporal bulges) o Male golden snub-nosed monkey Human dimorphism: Male facial hair & Female fat deposition in breasts, buttocks, and hips Hypotheses for breasts fat deposition - 1. Evolved via female-female competition that fat deposition indicates female quality (more=better) o Problem: Data do not support this hypothesis - 2. Indicative nutritional status (amount of body fat indicates ability to successfully reproduce) o Problem: breast size is NOT related to: Milk production & Fertility success - 3. Indicates time of ovulation o Problem: breast size in NOT largest when women are ovulating, but during pregnancy and lactation Body size sexual dimorphism in human  males larger - Due to physical
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