Marte Francelia Michell

Social relationships are a central determinant of fitness in animal societies, yet their role in shaping male life-history trajectories remains incompletely understood. In rhesus macaques (Macaca mulatta), social interactions are highly structured, emerging from patterns of affiliation, kinship, and cooperation rather than random association. These networks are known to influence survival, access to resources, and reproductive success. However, the extent to which variation in the quality and extent of male–male social bonds predicts longevity and reproductive outcomes remains an open question.

Here, I investigate the social behavior of male rhesus macaques in the free-ranging population of the Caribbean Primate Research Center at Cayo Santiago, Puerto Rico. Leveraging approximately 14 years of longitudinal demographic and behavioral data, I quantify patterns of grooming and spatial proximity to characterize male social networks. I then test how key factors—including age, social rank, and female availability, among others—shape the formation and persistence of male–male relationships, and whether these relationships translate into measurable fitness benefits. By linking social structure to survival and reproduction, this work aims to quantify social fitness gradients in male mammals, clarify the role of male–male bonds in the dispersing sex, and advance general theory on sociality, selection, and life-history evolution.

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