Post on 12-Jan-2016
Primate features
Life history
Brain size
… after Lemuriformes Lemur catta
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.
Brain size
Fleagle (1999) Primate Adaptation and Evolution
Neocortex
Neocortex
Responsible for cognitive abilities
Reasoning
Consciousness
In primates:
50-80% of the total brain’s volume !
Strier (2003) Primate Behavioral Ecology
Brain function
Neocortex The brain is expensive:
2% of human body size
20% of energy required to maintain its activities
! ! !
Strier (2003) Primate Behavioral Ecology
Neocortex - Medulla
Strier (2003) Primate Behavioral Ecology
Neocortex
MedullaMedulla
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: neocortex 20-50x larger• Humans: neocortex 105x larger
LogBrain
Weight
Log Body Weight
CO
G
Measuring relative brain size
1. Brain Weight as a function of Body Weight
2. EQ = Encephalization Quotient
= Observed / Expected brain size
Brain sizeAllometric
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
Mean for Mammals
Relativecranial capacity of macaques, gibbons, great apes and humans.
Decreasing relative cranial capacity as body weight increases.
Iwaniuk et al 2001 JCP
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
Reader & Laland 2002
Correlates of larger brains
Executive Brain Ratio=
(Neocortex + striatum) / (Brain stem)
Reader & Laland 2002
Correlates of larger brains
2. Social learning
1. Behavioral innovation
3. Tool-use
Executive Brain Ratio=
(Neocortex + striatum) / (Brain stem)
EBR and InnovationPositive relationship !
EBR and Social LearningPositive relationship !
Significant even when controlled for phylogeny
Identical results between EBR and Tool-use
Significant even when controlled for phylogeny
Members of large-brained primates
• innovate more often• learn from others more often• use tools more frequently
than small-brained primates
Reader & Laland 2002
Correlates of larger brains
May have played critical roles in primate brain evolution
Significance of the Executive Brain Ratio?
• Prosimians have smallest neocortex
ratios for their social group sizes
• Monkeys are intermediate
• Apes have the largest
Social Brain Hypothesis (Robin Dunbar)
Relationship between:
• size of neocortex
• size of social groups
Strier (2003) Primate Behavioral Ecology
Within each of these grades:
• Primates with the largest grooming
networks are those with the largest
neocortex ratios ! !
Social Brain Hypothesis (Robin Dunbar)
Strier (2003) Primate Behavioral Ecology
• The ability to maintain the social alliances was the
PRIMARY selective factor in the evolution of large
primate brains.
• Primates have social brains
Also in :
• Bats
• Carnivores
• Whales
Social Brain Hypothesis
Relationship between:
• size of neocortex
• size of social groups
Reader and Laland (2002)
Deacon 1997 Ann Rev Anthropol
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.
Developmental brain/body growth curves
Life History
Fleagle (1999) Primate Adaptation and Evolution
Life History
Fleagle (1999) Primate Adaptation and Evolution
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
Life History and BMR
Strier (2003) Primate Behavioral Ecology
Despite the large size differences between chimpanzees
and gorillas, they have remarkably similar life histories.
Among closely related primates, those with a higher BMRs and
larger brains tend to take longer to mature and to be slower to
reproduce.
Life History
Strier (2003) Primate Behavioral Ecology
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.
Fleagle (1999) Primate Adaptation and Evolution
Delayed maturation in
primates compared to
other mammals.
Furthermore in apes
compared to primates.
Further still in humans
compared to apes
Life History
Strier (2003) Primate Behavioral Ecology
Strier (2003) Primate Behavioral Ecology
HumanHumans and primates:s and primates:
• long period of slow childhood.
• growth accelerated at adolescence.
Mammals:Mammals:
• Growth curve decreases in rate from birth onward.
Human growth curve compared to non-primate mammals
MammalsMammals
HumansHumans
LemuriformesMadagascar:
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 ! !
LemuriformesDiversity 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
Daubentoniidae
1 spp. – middle finger tracking insects – large brain-body ratio
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
Indriidae - Indrids
3 genera
Unique locomotion
Rowe 1996 Pictorial guide to the living primates
Eulemur fulvus
albifrons
Eulemur fulvus fulvus
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
Eulemur macaco
• Sexual dichromatismSexual 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
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
Varecia variegata rubra
• Another subspecies
• Red form, black crown, white nape
Rowe 1996 Pictorial guide to the living primates
Lepilemur ruficaudatus• Deciduous dry forest• Mostly leaves, also fruit• Vagina closed, except mating season…
Microcebus myoxinus• Head & body length = 61 mm = 2.5 in.
• Testes increase in size when breeding season starts
Rowe 1996 Pictorial guide to the living primates
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
Photo by U. Thalmann. In Setchell and Curtis 2003. Field and laboratory methods in primatology.
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
Lemur catta Ring-tailed lemur
Dry-forest only
10,000 - 100,000 in wild
~ 1000 in zoos
3 - 3.5 kg
Diurnal, semi-terrestrial
Multi-F, multi-M
Female-philopatry
Cavigelli 1999 Anim Behav
Female hierarchy is linear
Female dominance:
nepotistic
Male dispersal
Like Female-Bonded Cercopithecines
Lemur catta Ringtail
Cavigelli 1999 Anim Behav
Promiscuous mating
Stable groups
(mean 18, multi-M)
Frequent aggression
Intergroup aggression,
(both sexes fight)
Wimmer & Kappeler 2002 Anim Behav
Like FB cercopithecines
Wimmer 2002
Like FB Cercopithecines
Higher-ranking males have
high Rep. Success despite:
• brief mating season
• no sexual signals
• promiscuous mating
Cavigelli 1999 Anim Behav
Like FB Cercopithecines
Higher-ranking females produce more cortisol
Sign of individual stress1. Late gestation period2. Feeding efforts were high3. Anti-predation behaviors
high
Wimmer 2002
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?
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)
Protect me !