No Evidence for a Link Between Dominance Rank, Unit Size, and Faecal Glucocorticoid Levels in a Small Sample of Wild female Guinea Baboons (Papio papio)

In response to environmental and social challenges, animals mount physiological “stress responses” involving elevated glucocorticoid (GC) levels, which may have long-term consequences for health and survival. However, the degree to which social factors drive these physiological responses is likely modulated by a species’ social system, including social organisation, dispersal patterns, and the steepness of the dominance hierarchy, which influence the costs and benefits of social interactions. We examined the relationship between dominance rank, unit size, and faecal GC metabolite (fGC) levels in wild female Guinea baboons (Papio papio). Guinea baboons live in multilevel societies with female-biased dispersal and shallow rank relationships. Units consisting of one primary male and associated females form the core of these societies. We hypothesised that females experience higher competition for male protection or access to food in larger units and that lower-ranking females would bear the costs of this competition. We predicted that membership in a larger unit and lower rank would be associated with higher fGC levels. We collected 251 faecal hormone samples from 14 individuals. A capture event during the sampling period allowed us to validate our method's sensitivity to stress responses. However, we found no evidence of a link between unit size or rank and fGC levels, suggesting that neither incurs a significant physiological cost in this species. These results extend our insights into the physiological correlates of behavioural variation in female primates, expanding our understanding of their adaptability and resilience to social stressors in relatively egalitarian multilevel societies with female-biased dispersal.