Models of Affiliative Relationships Among Free-Ranging Rhesus Monkeys (Macaca Mulatta)

Understanding the relative importance of various hypothesized organizing principles of affiliative relationships among female macaques has been problematic at least partly because researchers have lacked adequate statistical techniques for teasing apart the roles of maternal kinship and rank distance, and because criteria for kinship have varied across studies. We examined the extent to which maternal kinship and rank distance are independently associated with levels of affiliative interaction among free-ranging adult females rhesus monkeys (Macaca mulatta) on Cayo Santiago, Puerto Rico. We used a multiple regression extension of the Mantel test to evaluate three models, each using different criteria for kinship. In all three models, kinship emerged as a strong correlate of affiliative interaction. However, the degree to which rank distance correlated with affiliative interaction varied across models. Hence, the choice of criteria for kinship affected the apparent importance of rank distance in multi-generational groups. A model using graded rather than discrete criteria of kinship (i.e. degrees of relatedness instead of kin vs non-kin) but differentiating only close kin relationships (r 0.125) rather than all kin relationships (r 0.0005) accounted for the largest proportion of the total variance. These results support suggestions that adult female relationships are organized around several levels of kinship through maternal lines, and not simply by crude distinctions of kin vs non-kin. However, when kin are separated from common ancestors by more than a few links, females appear to behave towards related individuals much as they do toward non-kin.