Doctoral Dissertation Improvement: Variation in Macaque Social Structure from Phylogenetic, Socioecological and Biological Markets Principles

Social structure in nonhuman primates varies markedly both within and between species. Although there is no consensus, several explanations have been proposed. One is that social structure varies in accordance with species' past ancestral relationships (phylogenetic closeness). Two others are based on the idea that variation in current ecological factors (e.g., group size and/or food distribution) shapes patterns of competition within and between groups of the same species, and in turn, shapes (1) the structure of agonistic and dominance-related behavior, and/or (2) patterns of exchange of affiliative behavior (e.g., grooming, aggressive support) that occur as predicted by economic models (e.g., supply-and-demand). Research by doctoral student Krishna Balasubramaniam (University at Buffalo), supervised by Dr. Carol Berman, tests predictions related to these explanations, focusing on females in the primate genus Macaca. The investigators will reconstruct phylogenetic trees to decipher ancestral relationships, and use these to determine whether variation in dominance-related behavior across nine macaque species correlates with degrees of genetic relatedness. To test within-species explanations, they will collect observational behavioral data on free-ranging rhesus macaques at Cayo Santiago, Puerto Rico, using focal-animal and all-occurrences sampling. Various statistical analyses will be applied to these data to test whether group sizes and empirical measures of competitive ability vary with patterns of aggressive behavior, and/or the exchange of affiliative behavior The research is unique in testing predictions related to multiple explanations for variation of nonhuman primate social structure in a single study. It sheds light on the relative contributions of species' ancestral relationships vs. variation in current ecological conditions in shaping macaque social behavior, and addresses current debates concerning the relative roles of inherent species characteristics and/or stable environmental influences vs. adaptation to current conditions across primates, including early humans. In addition, aspects of the study related to patterns of exchange of affiliative behavior have important implications for understanding human economic behavior.