Predictors of social status in cynomolgus monkeys (Macaca fascicularis) after group formation

The purpose of the present study was to determine whether various behaviora l and hormonal markers obtained in individually housed monkeys would be pre dictive of social rank following group housing. Body weight, serum cortisol and testosterone levels, and locomotor activity in an open-field apparatus were examined in 20 experimentally naive male cynomolgus monkeys (Macaca f ascicularis) while they were individually housed. It was hypothesized that; eventual subordinate monkeys would have higher cortisol levels and increas ed locomotor activity scores. These monkeys were then placed in social grou ps of four (five pens of four monkeys), and social rank was determined base d on outcomes of dyadic agonistic encounters. Body weight correlated signif icantly with eventual social rank. In general, the heavier the monkey the h igher the social rank. Locomotor activity in an open-field apparatus follow ing administration of a low dose of cocaine (0.01 mg/kg, i.v.), which has b een shown to increase CNS dopamine, correlated with eventual social rank su ch that individually housed monkeys with high levels of locomotion were mor e likely to become subordinate. Serum cortisol and testosterone? levels fai led to correlate with eventual social rank. Hypothalamic-pituitary feedback sensitivity and adrenal responsiveness were examined by measuring cortisol levels after administration of dexamethasone and following ACTH challenge. Cortisol responses in these tests were not associated with eventual social rank. These results suggest that, in addition to body weight, the level of reactivity in a novel environment after administration of a low dose of co caine is a potential trait marker for social rank. This trait is apparently not associated with hormone levels, but; may involve other CNS mechanisms. (C) 2000 Wiley-Liss, Inc.