Behavioral and hormonal changes following social instability in young rhesus macaques (Macaca mulatta)

Abstract

Social instability (SI) occurs when there is competition over social status. Reduced certainty of social status can lead to heightened aggression, which can increase physiological stress responses, as individuals prepare to fight for their social status. However, adults can take proactive coping mechanisms to reduce the physiological stress induced by SI, such as increasing affiliation. Very little is known, however, about the behavioral and hormonal effects of SI early in development. Filling these gaps in knowledge would add to the fields of primatology and developmental and comparative psychology. We conducted an opportunistic study of a peer group of 18 rhesus macaque (Macaca mulatta) yearlings before and during SI. We used social network analysis to measure individuals’ dominance certainty (DC, in their aggressive and submissive network) and their position in affiliative networks (grooming and play) and analyzed hair cortisol concentrations (HCCs). As predicted, during SI, we observed a decrease in DC, indicating that individuals had less stable dominance positions. As well, during SI, we observed increased rates of social grooming and decreased rates of social play, reflecting potential coping mechanisms. More socially connected individuals in social grooming and social play networks received higher levels of coalitionary support. Contrary to predictions, DC did not predict HCCs; rather individuals that were more connected in the social play network exhibited smaller increases in HCCs during SI, revealing a potential buffering effect of social play. Our results underscore the need for further research on the effects of SI during ontogeny.