Anthropology Discussion 3

Lecture #12 — Primate Behavior II — Group Living and Managing Relationships Today’s Questions • How do primates manage group living? • How do male and female reproductive strategies differ? • What is sexual dimorphism? What causes it? Communication • Visual Communication – Appearance • Age, sex, rank, reproductive status • Autonomic Responses — involuntary – Facial Expressions and Gestures Facial Expressions and Gestures Vocalizations White -Handed Gibbon Duet Hylobates lar http://www.arkive.org/white - handed -gibbon/hylobates - lar/video -09b.html Vervet Monkey Alarm Calls Chlorocebus pygerythrus http://www.youtube.com/watch?v =hEzT -85gEdA Chimpanzee Vocalizations • The link will take you to a page with pant - hoots, pant -grunts, food calls, and screams. Take a listen! – http://gombechimpanzees.org/activities/vocal - communication/ Managing Social Relationships • Dominance Hierarchies • Agonistic Behavior • Affiliative Behavior Dominance Hierarchies • Organize social group – Reduces competition over access to resources – Provides predictability in social interactions • Priority of Access – Food – Mates – Reproductive Success • Learned and Enacted Toque Macaque Dominance Macaca Sinica • http://www.arkive.org/toque - macaque/macaca -sinica/video -08e.html Male Mountain Gorilla Display Gorilla gorilla berengei • http://www.arkive.org/eastern -gorilla/gorilla - beringei/video -be11.html Agonistic Behavior • Direct competition over resources – Aggression and submission – Can be very costly • Injury • Death • Energetic and physiological costs of conflict • Damaged Relationships Chimpanzees Fighting • http://www.arkive.org/chimpanzee/pan - troglodytes/video -03b.html Affiliative Behavior • GROOMING  Formation and maintenance of social relationships – Tolerance around resources – Gain access to resources through relationships – Support in agonistic contests – Social partners • Tolerance and Sharing • Conflict Resolution • Play Red Colobus Grooming Procolobus badius • http://www.arkive.org/western -red - colobus/procolobus -badius/video -05 Mountain Gorillas Play • http://www.arkive.org/eastern -gorilla/gorilla - beringei/video -be12 Bonobos Playing • http://www.arkive.org/bonobo/pan - paniscus/video -12a.html Reciprocal Altruism • Altruism – Self -sacrificing behavior • Kin -biased altruism – Investment in kin = investment in own genes • Non -Kin Altruism – Relationships matter – Investing in others  Others investing in you Reproduction and Reproductive Behaviors • Reproductive Strategies – K -selected species – r-selected species Reproductive Strategies • Females and Males face different reproductive challenges – Reproduction more costly for females • Females — resources, predator avoidance, infanticide avoidance – Female -Female competition for resources • Males — access to females – Male -Male competition for females Estrus Estrus • Strategy in multimale -multifemale , promiscuous groups – Females advertise receptivity through swellings, which induce competition among males – Peak swelling = peak fertility • In most species, females are only swollen right around ovulation, the rest of the menstrual cycle they are flat • In bonobos, females show a swelling near continuously  bonobos use sexual behavior in a variety of contexts Sperm Competition • In bonobos and chimpanzees, males compete directly over access to females but they also compete indirectly through sperm competition • Larger testis = more and healthier sperm produced – Sperm compete to reach the egg first • Relationship between relative testis size and mating system – Promiscuous, multimale system — males have very large testis relative to body size Sperm Competition Species Testis Size:Body Size Mating System Pan troglodytes 0.27 Multimale Pongo pygmaeus 0.05 Solitary Gorilla gorilla 0.02 Uni -Male Homo sapiens 0.06 Uni -Male/Pair - bonded Hylobates spp. 0.10 -0.11 Pair -bonded Sexual Selection and Sexual Dimorphism • In primates, most common in polygynous mating systems where there is significant male -male competition over access to females – body size – canine size • In pair -bonded species, sexual dimorphism is absent • In promiscuous, there is some size dimorphism but much less than in polygynous systems Sexual Selection Infanticide • Male strategy to increase reproductive success – Do not kill own offspring – Increases likelihood of mating with female • Transfer males in MM -MF groups • Outside males in Uni -Male groups – Bachelor Groups • Takeovers by new males