The complex relationship between behavioral attributes, social status, and whole blood serotonin in male Macaca...

Among group-housed male Cercopithecus aethiops, dominant animals have higher concentrations of whole bood serotonin (WBS) than their subordinate counterparts. In contrast, there appears to be no relationship between social status and WBS in Macaca nemestrina. We report here the relationship between social status and WBS among 29 male Macaca fascicularis housed in groups of five. Membership in these groups was disrupted periodically (20 times in 26 months) with a reorganization manipulation. Concentrations of WBS were assessed just prior to the 20th (final) social reorganization and at 1, 2, and 5 weeks following that reorganization. Correlations between these repeated samples were high, indicating considerable intraindividual stability in WBS. Overall, there were no persistent differences in WBS between clearly dominant (ranked 1 or 2) and subordinate (ranked 3, 4, or 5) monkeys, despite the substantial behavioral differences between such animals and the stability of social status across time. A multivariate analysis indicated that WBS was best predicted by a model that included a positive relationship with the interaction between rate of grooming and social status (P < 0.002), a negative relationship with extreme aggressiveness (P = 0.03), and a positive relationship with time spent alone (P < 0.04). Further analysis of the social status by grooming rate interaction revealed that WBS was higher in dominants than subordinates, but only if the dominants also initiated grooming frequently. These differences in the relationship WBS and social status in C. aethiops and M. fascicularis may reflect differences in the behavioral dynamics underlying the dominance hierarchies in small groups of these two species.