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Primate features

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  1. Primate features Brain size Life history … after Lemuriformes Lemur catta

  2. Brain Although the human brain is 3 to 4 times heavier than the chimpanzee brain, there is considerable similarity between the 2 species in convolutional details. Tattersall, Delson, van Couvering (1988) Encyclopedia of human evolution and prehistory.

  3. Brain size Fleagle (1999) Primate Adaptation and Evolution

  4. Neocortex Neocortex Responsible for cognitive abilities Reasoning Consciousness In primates: 50-80% of the total brain’s volume ! Strier (2003) Primate Behavioral Ecology

  5. Neocortex Brain function The brain is expensive: 2% of human body size 20% of energy required to maintain its activities ! ! ! Strier (2003) Primate Behavioral Ecology

  6. Neocortex Neocortex - Medulla Medulla Primitive part of the brain that controls basic body function such as respiration and heart rate. • Insectivorous mammals: neocortex same size than medulla • Prosimians: neocortex 10x larger • Monkeys/Apes: neocortex20-50x larger • Humans: neocortex105x larger Strier (2003) Primate Behavioral Ecology

  7. O C G Log Brain Weight Log Body Weight Measuring relative brain size • Brain Weight as a function of Body Weight • EQ = Encephalization Quotient • = Observed / Expected brain size

  8. Mean for Mammals Brain size Allometric relationship between brain and body weight for 309 extant placental mammals. Nest to humans? Dolphins! Primates have larger brain size ratio than the “mean mammal” Strier (2003) Primate Behavioral Ecology

  9. Relative cranial capacity of macaques, gibbons, great apes and humans. Decreasing relative cranial capacity as body weight increases.

  10. Correlates of larger brains : PLAY Larger-brained mammals play more than smaller-brained This is true between different Orders of mammals But not within the Orders of Primates or Rodents 15 mammalian orders Iwaniuk et al 2001 JCP

  11. Correlates of larger brains Executive Brain Ratio= (Neocortex + striatum) / (Brain stem) Reader & Laland 2002

  12. Correlates of larger brains Executive Brain Ratio= (Neocortex + striatum) / (Brain stem) 1. Behavioral innovation 2. Social learning 3. Tool-use Reader & Laland 2002

  13. EBR and Innovation Positive relationship ! Significant even when controlled for phylogeny Identical results between EBR and Tool-use EBR and Social Learning Positive relationship ! Significant even when controlled for phylogeny

  14. Correlates of larger brains Significance of the Executive Brain Ratio? • Members of large-brained primates • innovate more often • learn from others more often • use tools more frequently • than small-brained primates May have played critical roles in primate brain evolution Reader & Laland 2002

  15. Social Brain Hypothesis (Robin Dunbar) • Relationship between: • size of neocortex • size of social groups • Prosimians have smallest neocortex ratios for their social group sizes • Monkeys are intermediate • Apes have the largest Strier (2003) Primate Behavioral Ecology

  16. Social Brain Hypothesis (Robin Dunbar) • Within each of these grades: • Primates with the largest grooming networks are those with the largest neocortex ratios ! ! • The ability to maintain the social alliances was the PRIMARY selective factor in the evolution of large primate brains. • Primates have social brains Strier (2003) Primate Behavioral Ecology

  17. Social Brain Hypothesis • Relationship between: • size of neocortex • size of social groups • Also in : • Bats • Carnivores • Whales Reader and Laland (2002)

  18. Developmental brain/body growth curves Left figure: General pattern throughout life, showing brain growth slows down earlier than the rest of the body. Right figure: Prenatal general pattern, showing the same brain growth for all mammals surveyed. This demonstrates that the left-shifted primate growth is NOT the result of faster brain growth, but a reduced body growth. Deacon 1997 Ann Rev Anthropol

  19. Life History Fleagle (1999) Primate Adaptation and Evolution

  20. Life History • The most obvious correlate of life history variation is body size. • Larger species: • larger brain size ratio • longer gestation • fewer infants • larger infants • longer weaning ages • delayed sexual maturity ? • slower reproduction Fleagle (1999) Primate Adaptation and Evolution

  21. Life History and BMR Among closely related primates, those with a higher BMRs and larger brains tend to take longer to mature and to be slower to reproduce. Despite the large size differences between chimpanzees and gorillas, they have remarkably similar life histories. Strier (2003) Primate Behavioral Ecology

  22. Life History • Large-bodied primates need to eat more food than smaller primates. • In absolute terms, their energetic requirements are greater. • In relative terms, they need less energy per unit of body weight. Strier (2003) Primate Behavioral Ecology

  23. Delayed maturation in primates compared to other mammals. Furthermore in apes compared to primates. Further still in humans compared to apes Fleagle (1999) Primate Adaptation and Evolution

  24. Life History Strier (2003) Primate Behavioral Ecology

  25. Human growth curve compared to non-primate mammals Mammals Humans • Humans and primates: • long period of slow childhood. • growth accelerated at adolescence. • Mammals: • Growth curve decreases in rate from birth onward. Strier (2003) Primate Behavioral Ecology

  26. Lemuriformes Madagascar: Single colonization event ~ 50 mya 5 families with > 60 species Humans arrived 1500 years ago on Madag. ONE-THIRD of all the lemurs disappeared ! ! Subfossils = large, slow moving, diurnal = easy prey, lots of meat ! !

  27. Lemuriformes Diversity in social behavior Similarities with higher primates:  Convergence offers tests of socioecological principles Little sexual dimorphism in body size and weight In lemur species which lives in social groups  Females are dominant to males

  28. Indriidae - Indrids 3 genera Unique locomotion Cheirogaleidae – Dwarf lemurs Smallest primate = 30 g ! ! Megaladapidae (was Lepilemuridae) Sportive lemurs – nocturnal – adults lose their upper incisors ! Chromosomal evidence = 7 spp. Lemuridae 4 genera – most well known – high adaptability in zoos LEMURIFORMES Daubentoniidae 1 spp. – middle finger tracking insects – large brain-body ratio Rowe 1996 Pictorial guide to the living primates

  29. Eulemur fulvus fulvus Eulemur fulvus albifrons Eulemur fulvus rufus • Eulemur = • 6 spp. with different head color patterns • Primary closed canopy forests • Fruit, mature leaves, flowers, bark, sap, • dirt, insects. • Sexual maturity females = 10 months ! Rowe 1996 Pictorial guide to the living primates

  30. Eulemur macaco • Sexual dichromatism:the condition in which males and females of a species differ in color. • Primary & secondary • Timber, plantations (cashew and coffee) • Males aggressive during mating season • One male observed to mate 6 times in 30 min... Female Male Rowe 1996 Pictorial guide to the living primates

  31. Varecia variegata • Ruffed lemur • Intermembral index: 72 ! • First to disappear (logging) • Large fruits from large trees • Pass seeds in 2-3 hours (good seed dispersers…) Rowe 1996 Pictorial guide to the living primates

  32. Varecia variegata rubra • Another subspecies • Red form, black crown, white nape Rowe 1996 Pictorial guide to the living primates

  33. Microcebus myoxinus • Head & body length = 61 mm = 2.5 in. • Testes increase in size when breeding season starts • Lepilemur ruficaudatus • Deciduous dry forest • Mostly leaves, also fruit • Vagina closed, except mating season… Rowe 1996 Pictorial guide to the living primates

  34. Indriidae: Propithecus verreauxi • Sifaka (after their barking call) • Mating season = Jan to Mar. • Females ovulate only once (!) • Receptive for only 12-36 hrs (!) • Females dominant over males (!) • Males fight for dominance during the mating season only. Why? • Because females mate with the alpha male only (!) Rowe 1996 Pictorial guide to the living primates

  35. Cheirogaleus medius • Nocturnal and arboreal • Collar to track them • Hibernation 7-9 months • Body temperature drops from 33-38 C to 15 C • Can lose up to 100 g • (normal weight: 142-217 g) • Hibernate in hollow tree trunk during dry season • Solitary foraging but hibernate with 3-5 other members • Feeds on chameleons (!) Data from Rowe 1996 Pictorial guide to the living primates Photo by U. Thalmann. In Setchell and Curtis 2003. Field and laboratory methods in primatology.

  36. Lemur cattaRing-tailed lemur 3 - 3.5 kg Dry-forest only 10,000 - 100,000 in wild ~ 1000 in zoos

  37. Like Female-Bonded Cercopithecines Diurnal, semi-terrestrial Multi-F, multi-M Female-philopatry Male dispersal Female hierarchy is linear Female dominance: nepotistic Cavigelli 1999 Anim Behav

  38. Lemur catta Ringtail Like FB cercopithecines Stable groups (mean 18, multi-M) Frequent aggression Intergroup aggression, (both sexes fight) Promiscuous mating Wimmer & Kappeler 2002 Anim Behav Cavigelli 1999 Anim Behav

  39. Like FB Cercopithecines • Higher-ranking males have • high Rep. Success despite: • brief mating season • no sexual signals • promiscuous mating Wimmer 2002

  40. Sign of individual stress • Late gestation period • Feeding efforts were high • Anti-predation behaviors high Like FB Cercopithecines Higher-ranking females produce more cortisol Cavigelli 1999 Anim Behav

  41. Unlike FB Cercopithecines Fewer females (single matriline) Equal sex ratio among adults Brief synchronous mating season (2-4 days) (No prominent sexual signals) i.e. more intense male mating competition? Wimmer 2002

  42. Unlike FB Cercopithecines No sexual dimorphism in size FF dominate MM completely No F-M friendships (contra Smuts’ study of F-M friendship among baboons)

  43. Protect me !