Muriqui the Pacific Black Face

Muriqui lives in social groups of up to 35 individuals, including some males and adult females, existing apparently a great variability about intra-group spacement and social structure in the different populations. It is believed that a social organization sufficiently fluid exists in muriqui society, where male and female overlap the use areas, what it becomes difficult the characterisation of the groups and sub-groups that can vary in its composition.

Some studies had shown that a small percentage of the time of the diurnal activity is spent with social interactions. Despite this, some categories of social behavior, specially embraces call the attention for its intensity, frequently occurring when meeting between muriquis are observed, or when muriquis find animals of other species; also they occur during the meeting of troops or as a form of ritualised salutation between individuals apparently related, however even if they met for some time, these behaviours seem to reinforce mutual solidarity . Embraces are also characterised by the high frequency where the individuals mutually initiate it, showing that the it happens for reattachment of fraternal relations.

However despite the little dedicated time for the social interactions, adult Muriquis rarely are engaged in aggressive interactions, being considered a extremity between primates species for its low aggressiveness; This is a main distinguishing factor of this primates genus, when compared to others primate species, that normally present high levels of aggressiveness within the group individuals.

Muriqui presents great tolerance between individuals, and frequently they forage, move and rest in close spatial proximity, without signs of direct competition has been observed. That is particularly interesting between the males adults of the same group that although to remain close to one another is not engaged in direct competitions, also for available reproductive females.

The system reproductive it can be characterised as promiscuous. Adult females in oestrous (the female during copulation emits a vocalisation and presents characteristic facial expression.) are receptive to all adult males of the group, being able to copulate with some males in a short space of time without that monopoly or attempts of interruption of cópula by any males.

This behavior differentiates them of Old World Primates as well, showing a particular behavioural strategy, with a low index of aggressiveness and a differentiated sexual behavior where a female can be fertilised by some males.

• They are considered most pacific of the primates in the World. But, why are these primates so different of the others ??
• Which evolutive advantage they had got allowing for this behaviour has being fixed ?
• There are some intrigating questions and theories that try to clarify this doubt: The low text caloric of its basically vegetarian diet would imply in an energy restriction so, the individuals to participate of social interactions mainly aggressive?
• Its varied diet and the food distribution can make possible that individuals prevent direct competition feeding itself in alternative sources?
• Due to its size and its necessity to distribute its weight, frequently all members are used including the tail, to engage itself though an incited dispute could cause one fall that stops an animal of heavy as muriqui it could cause serious wounds even though or the death?

Between the males two theories can be listed: A high degree of consanguinity, between relatives would not arise a necessity for direct females competition. It can be still argued that a direct female competition has been substituted for sperm competition. This hypothesis is based on the size of the escrotum of adult males, and on the amount of sperm that after drains of the vaginal socket of the females genitals after copulating. . However, scientific research are underway and many others still will be projected to solve this question. It becomes important to stand out that the studies carried through in the different populations of muriquis, either in forest fragments or continuous portions of Atlantic Forest will supply new elements and information for the knowledge of the species, addressing how are this mechanisms and how the different factors act jointly or not for these features of low level aggressiveness between individuals.

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