Name: Carla de Borba Possamai
Type: PhD thesis
Publication date: 25/06/2013

Namesort descending Role
Karen Barbara Strier Advisor *

Examining board:

Namesort descending Role
Albert David Ditchfield Internal Examiner *
Cristiane Cäsar Coelho Dantas External Examiner *
Daniel Marques de Almeida Pessoa External Examiner *
Karen Barbara Strier Advisor *
Sérgio Lucena Mendes Internal Examiner *

Summary: Most species of mammals live in social groups and form close relationships with their conspecifics. In primates these groups may vary in the degree of cohesion and composition, with the latter being determined in part by patterns of dispersal. Living in groups provides primates the context within which each individual must make decisions that will ensure survival and reproductive success, however, the stability of groups depends on the ability of individuals to recognize and remember with whom they have interacted. Humans, for example, use faces for important information on the identity, sex, age and intentions of their conspecific that is essential for life in complex societies, and there is evidence that nonhuman primates process the information contained in the face in a similar way. Many primates show a wide variation in coat and skin color and it is believed that the conspicuous signals advertised by these variations are directed to their conspecifics as a means of visual communication. Primates are highly social and able to communicate and interact with any member of the group but family ties are more important and cooperation and preferential associations with related individuals are known to bring more direct and indirect benefits. Typically social relationships of the philopatric members of a group are intense and it is believed that the sex that disperses is usually less social. However, there are mechanisms that can assist the process of recognition of individuals and kin among primates, and the most likely are familiarity and phenotype matching. The northern muriqui (Brachyteles hypoxanthus), the subject of this study, has some morphological characteristics that may be advantageous for individual recognition and that may be used to facilitate social relationships. Northern muriquis are born with dark skins but as they mature they begin to undergo a process of depigmentation forming different patterns that are unique to each individual. Their social relations are egalitarian, and the social structure, similar to chimpanzees and spider monkeys, is patrilocal and in this species females are responsible for dispersal. How and with whom females develop and maintain social relationships after dispersal are still not known. However, northern muriquis give us the opportunity to investigate and deepen the understanding of the mechanisms that can influence the choices of females by potential social relationships with their maternal kin and other females known from natal group even after being established in a new group. In this study we aimed to answer three questions: First, do maternally related individuals have similar facial features; second, are humans able to recognize facial similarities in maternally related northern muriquis monkeys; and last, do female northern muriqui monkeys demonstrate preferential associations and more affiliative interactions with females that are maternally related and/or known previously from their natal groups. To answer the first two questions we used photographs of faces of the northern muriquis. First we evaluated whether facial pigmentation patterns presented similarities, however, our results did not show similarities that reflect maternal kinship among the muriquis. Second, we evaluated the ability of humans to recognize the facial similarities of maternally related versus unrelated muriquis from their photos. The results of this study did not corroborate our prediction that maternally related northern muriquis have facial similarities that humans would be able to detect. Finally, we evaluated the social relationships of adult females of three of the groups that make up the population of the northern muriquis of the RPPN-Feliciano Miguel Abdala using behavioral data collected from January to December 2011. As predicted, associations among adult females were more frequent than with other group members. However, contrary to our predictions, females did not associate preferentially with other females that were known/and or maternally related from their natal groups compared to females that were neither familiar or maternally related. Therefore our results did not reveal evidence that familiarity or maternal kin recognition had an influence on female social relationships post-dispersal.
Keywords: northern muriquis (Brachyteles hypoxanthus), affiliative relationships, facial recognition, recognition of kinship, phenotype matching, familiarity, females, dispersal.

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