Primate features

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

! ! !


Neocortex - Medulla


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”


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)



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



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


Within each of these grades:

• Primates with the largest grooming

networks are those with the largest

neocortex ratios ! !

Social Brain Hypothesis (Robin Dunbar)


• 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


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

Life History and BMR


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


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.


Delayed maturation in

primates compared to

other mammals.

Furthermore in apes

compared to primates.

Further still in humans

compared to apes

Life History



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 !


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


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


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


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


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


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 !

Primate features

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