3/12/2014 1 Part 1: Primate Mating & Social Systems Part 2: Paleomethods 1 Course Business • Midterm issues – Question 19: In small, isolated populations, genetic drift is a major evolutionary force. What does genetic drift do to populations over time? • Creates populations that are more like each other • Creates populations that are less like each other – Question 22: The function of mRNA is to: • Copy and carry the code of a gene to the ribosome 23/12/2014 2 Today • Finish matting systems – Focus on primates • Paleo methods and record of paleo climate and environments 3 43/12/2014 3 Mating Systems • Animals generally don’t mate at random • Males and females often differ in their criteria for mates – and often differ in their preferences 5 What do females want? • Resources (especially food need to grow babies) • Good genes • Help with parenting – Carrying, feeding the baby (i.e., finding extra food) – A rarity for most mammals, including primates • No infanticide – Protection 63/12/2014 4 What do males want? • Mating opportunities (i.e., more sex) • More mating opportunities • Paternity certainty 7 Sexual selection • Traits selected for that are involved in mating • “Goal” of both sexes is to successfully pass on genes – fitness! • Reproductive limitations on the sexes are different – Different “strategies” for optimizing resources for reproductive effort – Inter-sexual choice (female choice) – Intra-sexual competition (male-male competition) 83/12/2014 5 Relative parental investment is the key variable in controlling sexual selection In what ways can one invest? 9 Differential Parental Investment Females • Large gametes • Internal gestation • Lactation • Lengthy period of maternal investment Males • Small gametes • Parental investment period is variable • Male-male competition 103/12/2014 6 Reproductive Investment (Typical Mammalian Pattern) 11 Competition Mating Gestation Lactation Loser Males MALES FEMALES Reproductive Investment • The sex investing most becomes a limiting resource for the sex investing the least; competition for the investing sex will take place • Males limited by the ability to fertilize eggs • Females limited by the ability to produce eggs (also mature offspring) • Primate social systems are based partly on resource distribution (consider female contribution as resource) 123/12/2014 7 Patchy distribution of resources 13 Females map onto resources 143/12/2014 8 Males map onto females 15 Even distribution of resources 163/12/2014 9 Females map onto resources 17 Males map onto females 183/12/2014 10 How do male primates compete? • Canine size dimorphism • Sexual dimorphism specific trait body size • Sperm competition 19 Human Chimpanzee Gorilla Orangutan Baboon © Kornelius Kupczik, Max Planck Institute of Evolutionary Anthropology 203/12/2014 11 Goals of male competition • Males invest less in offspring than females do, so male reproductive success depends mostly on gaining access to females • Female-female competition? 21 Correlation between sexually dimorphic traits and degree of polygyny 223/12/2014 12 Mating systems and sperm competition 23 Why do gorillas have the smallest? Mating systems and sperm competition 243/12/2014 13 Any Questions? 25 Dominance Hierarchies (both sexes have them) Female baboons in Amboseli National Park (Kenya) transfer their rank to their daughters 263/12/2014 14 Why do you want to be higher in the dominance hierarchy? To produce more offspring!! 27 For males, high status = access to mating opportunities 283/12/2014 15 For females, high status = more offspring 29 For females, high status = greater likelihood of offspring survival 303/12/2014 16 For females, high status = faster maturation rate in daughters 31 Dominance hierarchy and reproductive success • What is the mechanism behind this relationship? – Access to better quality and quantity of food – Confrontations produce stress in lower ranked individuals • Stress leads to high cortisol levels, which leads to negative health effects 323/12/2014 17 Any Questions? 33 Summary: primate social behavior • Mating systems – Solitary – Polyandry – Polygyny (single male, multi-male, fission-fusion) • Reproductive investment • Competition: inter and intra-sex – Female – Male 343/12/2014 18 Specific examples of primate social groups… 35 Polyandry – Marmosets & Tamarins • Patchy food distribution (gum) – Small group size that defends food source • Twins require more paternal care, so no RS without paternal investment – No male-male competition 363/12/2014 19 Multi-male polygyny – Savanna Baboon (and many other OWM) • Even food distribution (grass) – Resource defense impossible • Moderate sexual dimorphism with male social hierarchy and male-female “friendships” 37 Single-male polygyny – Hamadryas Baboon • Patchy, terrestrial food distribution – Female defense possible • Moderately high sexual dimorphism due to male-male competition of female unit 383/12/2014 20 Monogamy – gibbons and siamang • Patchy, seasonal food distribution • Monomorphic in size with low male-male competition (dimorphic in color) • Monogamous pairs defend their territory with verbal calls, while male frequently grooms the female (i.e., mate guarding) 39 Solitary (polygyny) – orangutan • Patchy, seasonal food distribution • Group size limited to mother and offspring, long offspring dependency • Extreme male-male competition results in high sexual dimorphism 403/12/2014 21 Solitary (polygyny) – orangutan • Extreme sexual dimorphism • Body weight index of dimorphism Male/female = 175 lbs/86 lbs = 2.02 41 Solitary (polygyny) – orangutan two male strategies 423/12/2014 22 One male polygyny – gorilla • Even food distribution (mostly terrestrial herbaceous vegetation) – Resource defense impossible • Extreme male-male competition selecting for high sexual dimorphism 43 One male polygyny – gorilla • Given the food distribution, why does gorilla society look like a one-male unit? – Would expect a multi-male unit… 443/12/2014 23 One male polygyny – gorilla • Infanticide! • Long lactation period = long interbirth interval – Remove infant, lactation stops, ovulation begins • After a takeover, males kill all nursing infants – Unrelated males are a threat to infants •
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