The dominance structure of primate social groups varies widely. In addition to the groups’ composition, intrinsic attributes such as sex, body size and life experience are important factors that can affect hierarchical dominance relations. All primates are social animals, and the social environment has a direct influence on the physiological conditions of vital systems such as immunological, reproductive and cardiovascular systems. In this study, we analyze the hierarchical structure of Saimiri collinsi in captivity, including the hierarchical structure type, the influence of individual intrinsic characteristics (sex, age, weight and origin—born in captivity or in the wild) based on the prior-attributes model, the relation between agonistic behavior frequency and hierarchical position, and hierarchy steepness, which represents the dominance gradient. We found that the group order was characterized by a partial hierarchy: a dominance position could be occupied by more than one individual simultaneously, including individuals of both sexes. Intrinsic characteristics had no influence on hierarchical structure, with the exception of the male in the highest hierarchical position, which had a markedly larger body than all other group members. Thus, the prior-attributes model did not apply to hierarchical formation of S. collinsi in captivity. Only the frequency of agonistic behavior of males correlated with their hierarchical position, and they differed from all other group members in their more aggressive behavior. The steepness between adjacent positions along the dominance gradient was significant only between the dominant male and the next individual in the group, with a smooth gradient between the other positions in the rank. As the access to resources is directly related to hierarchical dominance, a smooth dominance gradient is to be expected in species that form very large groups, such as wild Saimiri populations.
Dominance hierarchy Prior-attributes model Dominance strategies Neotropical primates
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This work received CAPES funding through a doctoral grant awarded by the Programa de Pós-Graduação em Zoologia of the Universidade Federal do Pará and Museu Paraense Emílio Goeldi and a research grant by Instituto de Desenvolvimento Sustentável Mamirauá (CNPq: 312791/2015-1).We thank the Centro Nacional de Primatas for allowing this work and for logistic support, and individually to Paulo Castro, Karol Oliveira and Dojean Froes for their direct assistance with methodological procedures in this research. We also thank Patrícia Izar for her valuable instructions about primate social systems.
This project was licensed by the Ethics Committee on the Use of Animals (CEUA) of the Evandro Chagas Institute, Pará, Brazil. The CEUA evaluates the methodological procedures employed in research projects, based on the ethical norms and standards for research involving animals according to Art. 18 of Decree no. 6899, of July 15, 2009, Brazil.
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