Ring-tailed lemur Muriqui

1. Sexual monomorphism vs. dimorphism

2. Competition and social relationships

“Phylogeny of behavior”

primates

Female body size

M/F body weight

SEXUAL DIMORPHISM IN BODY WEIGHT tends to INCREASE WITH BODY MASS (RENSCH’S RULE)

1.0

1.4

1.8

2.2

Monogamy Multi-malegroup

One-malegroup

M/F body weight

More Females per Male

Sexual Dimorphism in Body-Weight increases with # FF per M in group

0.5

1.5

2.5

M/F Canine height

Monogamy Multi-malegroup

One-malegroup

More Females per Male

Sexual Dimorphism in Canine Height increases with# FF per M in group

i.e. importance of male fighting ability depends onOPERATIONAL SEX RATIO (OSR)

More intense fighting expected if:1. More males present at mating time2. Fewer females3. Longer interbirth intervals (IBI), e.g. Pongo4. Shorter period of female sexual receptivity

OSR =# males * IBI

# females * # mating days/birth

Mitani et al.(1996)

“Polygynous primates”- But data are from Anthropoids!

R = 0.49, P < 0.012

Higher OSRHigher Sex. Dim.

Scramble competitionAll individuals equally affected

e.g. Social group feeding in a treeResources not economically defensible

e.g. Mature leavesFighting doesn’t help

Competition

Resources are in short supply

Contest competitionWinners do better than losersResources are defensible : e.g. fruits in a treeFighting or dominance helps : Higher feeding rates

COMPETITION AND RELATIONSHIPS

Competitive regimes

WGS = Within-group scramble

WGC = Within-group contest

BGS = Between-group scramble

BGC = Between-group contest

Competitive regimes and expected relationships: females

Rep Success high if

Aggression

Agonistic kin support

Dominance

Rank stability

Hierarchy

Strong WGS

Group Size low

Rare

Rare

Inconsistent

Low

Egalitarian, individualistic

Strong WGC

Rank high

Common

Common

Unidirectional

High

Despotic, nepotistic

van Schaik (1989)

E.g. Baboon, ringtail Muriqui, bonobo

Sakis, Uakaris, Titis• Part of the cebid group - Pitheciines (New World monkeys)

• Many species Callicebus titi monkey (10 species)

Cacajao uakari (2 species)

Chiropotes bearded saki (2 species)

Pithecia saki monkey (6 species)

For photographs and brief account per species, see Primate Info Networkhttp://pin.primate.wisc.edu/av/images

Callicebus cupreus discolor

Monomorphic in body size and colorSmall, cohesive monogamous group

Males are paternalisticTerritorial

Callicebus moloch ornatus

Callicebus donacophilus

Callicebus personatus nigrifrons

Callicebus personatus

Cacajao calvus

BEARDED SAKIS AND UAKARISOpposite of titi monkeys

Large, more loosely structured groupsGroups fission smaller feeding parties

Large home rangesLarge day ranges

Males : no paternal careLittle sexual dimorphism body mass/color

Chiropotes satanas

Chiropotes albinasus

Pithecia monachus

SAKISIntermediate between

titis/bearded sakis/uakarisSexual dichromatism, bushy tail

Small group size, small body massTerritorial

Mothers are care-giversMales more as infants grow up

Aggressive intergroup encounters

Pithecia pithecia

MuriquiSmall sexual dimorphism

Females 9.5 kg Males 12 kg

Small canines in both sexes

Ripe fruit preferred

- but > 50% feeding time on leaf

- up to 80-90% in dry season

Large testes (high WCS)

CONSERVATION ISSUE:

ca 400 in wild, < 10 (?) in captivity

Muriqui social behaviorGroups 15-60; stable OR

“Molecular fission-fusion”

INTERGROUP

Male philopatry; female dispersal @ 5-6 years

Non-territorial, but…

… Aggressive intergroup at key foods FF+MM active players

… Mostly vocalizations rather than physical fights.

INTRAGROUP

Very little aggression

Egalitarian year-round

Resource displacement = rare

Kin support = rare

Rank stability low

No contest competition for sex (!)

FF brief estrus, solicit MM

No mate-guarding

Embracing

Muriqui social behavior

Predictions for Male-male

Scramble competition

MM closer when resting > feeding

M mating success @ M-F association

Sharing occurs when F at ovulation

Strier et al. (2002) Behaviour

Predictions for Male-male

Bonding system

MM bonds occur

MM value specific MM

MM ‘allies’ share FF

Maternal brother don’t associate but…

… Brothers share FF during mating

Strier et al. (2002) Behaviour

PredictionsMM closer when resting > feeding

MM bonds occur

MM value specific MM (high-maters)

MM ‘allies’ share F mating

M mating success @ M-F association

MM that share FF tend to be kin

Puzzles.

Why are some MM attractive to other MM? Age-related?

Why do MM tolerate “high-approachers”?

?

Strier et al. (2002) Behaviour

Sexual BehaviorEstrous FF mate promiscuously

Several MM may line up to mate

After intromission, the M is motionless for 2-7 minutes (!)

10-28 of thrusting

The M’s ejaculate hardens to form a vaginal plug but…

… removed by the female or other males and dropped.

Adults deposit urine on their hands (?)

Rowe (1996) Pictorial guide to the primates

Measuring relationship value“Hinde index” for a dyad:

“% approaches - % leaves”

50%

0

-50%

Hinde index for body contacts

= (% body contacts initiated by Infant) - (% body contacts terminated by Infant) Rhesus monkeys

Answer : The mother !

}}

I joins, M leave

M joins, I leave

Q: Who’s responsible for mother-infant contact declining as infant grows?

Infant age (weeks)

12 weeks

Will you protect me ?

Wrangham and Pilbeam 2001. In All Apes Great and Small

Reconstructing the past