Fecal glucocorticoid metabolite relates to social rank in Sichuan snub-nosed monkeys

Studies suggest there is a connection between adrenal cortisol production and social rank in many non-human primates. Behavioral observations have confirmed that Sichuan snub-nosed monkeys (Rhinopithecus roxellana) have obvious social ranks. Thus, the goal of this study was to investigate whether there is a relationship between fecal glucocorticoid metabolite (FGM) concentrations as an indicator of social stress and dominance rank in Sichuan snub-nosed monkeys. Fecal samples were collected about every 5 days for 1 year from 10 Sichuan snub-nosed monkeys (> 7 years old; n = 5 males, 5 females), and analysed for FGM with a corticosterone radioimmunoassay using machine learning and open access data. Results showed that: (1) yearly mean FGM levels were negatively correlated with individual animal behavioral social rank in both males and females; (2) we divided the whole year into warm and cold seasons (seasonally) and breeding and nonbreeding seasons physiologically. Except for cold seasons, FGM levels have a negative correlation with behavioral social ranks in males and females; (3) female rank does not clearly relate to FGM levels; (4) social ranks of snub-nosed monkeys are more collaborative traits than aggressive ones. Our findings have important implications for understanding the different physiological consequences of dominant and subordinate social status on Sichuan snub-nosed monkey societies, and it quantifies how physiological stress differs during seasons and phases, and by individuals.