Behavioral and adrenocortical responses of male cynomolgus and lion-tailed macaques to social stimulation and group formation

Several recent studies indicate that primate species may differ in behavioral, and in some instances physiological, responses to social manipulations. These differences in response dispositions have been interpreted as being based on temperamental differences among species. This report extends previous comparative studies of macaques by describing behavioral contrasts observed between males of two macaque species, lion-tailed and cynomolgus macaques, in response to social manipulations. Males were exposed to a mirror, then visually exposed to conspecific neighbors in all pairwise combinations, and then formed into conspecific social groups. Urine samples were collected in the pairing and group formation conditions for cortisol assay. The cynomolgus demonstrated more affiliative behavior than the lion-tails in all conditions, while the lion-tails tended to exhibit more aggressive behavior. Following group formation cortisol values showed a decreasing trend in the cynomolgus, but not in the lion-tails. The cynomolgus rapidly adapted to group living and relations between them were primarily affiliative. In contrast, no affiliative behavior was ever observed in the lion-tail group, which appeared to be highly stressed by group living and was eventually disbanded.