Not all grooming is equal: differential effects of political vs affiliative grooming on cytokines and glucocorticoids in rhesus macaques

Positive social relationships in humans are known to have health promoting effects while negative social relationships have detrimental effects. Features of the broader social network, including indirect connections, also impact health. However, complicating our ability to examine these features, human networks are diverse and difficult to fully quantify. Animal models where social networks can be fully characterized are useful in examining how structurally similar yet functionally different relationships can differentially relate to biomarkers of health. For example, in nonhuman primates, grooming serves two main functions, to maintain social bonds (family/friends networks) or gain access to resources/support (political networks). We examined whether an individual’s position in these two network types was differentially related to biomarkers of inflammation and physiological stress in female rhesus macaques (Macaca mulatta). Consistent with predictions, females with higher family/friends centrality had lower IL-6/TNF-α levels, while females with high political centrality showed elevated levels. Middle-ranking females with high political centrality showed elevated hair cortisol yet little to no benefit of family/friend centrality. These results indicate that while grooming interactions are structurally similar, they may be functionally distinct and therefore have very different, even opposite, effects on health. Affiliative interactions occurring within the context of an established relationship (i.e., family/friends) can provide opportunities for social buffering. In contrast, interactions among individuals without established relationships, even friendly interactions, may ultimately be physiologically costly. Ultimately, these results indicate that while social relationships may appear similar, the underlying functionality can have fundamentally diverse physiological outcomes.