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

Abstract

The purpose of the present study was to determine whether various behavioral and hormonal markers obtained in individually housed monkeys would be predictive 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 fascicularis) while they were individually housed. It was hypothesized that eventual subordinate monkeys would have higher cortisol levels and increased locomotor activity scores. These monkeys were then placed in social groups of four (five pens of four monkeys), and social rank was determined based on outcomes of dyadic agonistic encounters. Body weight correlated significantly with eventual social rank. In general, the heavier the monkey the higher the social rank. Locomotor activity in an open‐field apparatus following administration of a low dose of cocaine (0.01 mg/kg, i.v.), which has been shown to increase CNS dopamine, correlated with eventual social rank such that individually housed monkeys with high levels of locomotion were more likely to become subordinate. Serum cortisol and testosterone levels failed 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 cocaine is a potential trait marker for social rank. This trait is apparently not associated with hormone levels, but may involve other CNS mechanisms. Am. J. Primatol. 52:115–131, 2000. © 2000 Wiley‐Liss, Inc.

Polymorphisms in the serotonin reuptake transporter gene modify the consequences of social status on metabolic health in female rhesus monkeys

“…There was more variance in body mass measures and T3 concentrations in l/l females compared to svariant females at baseline when social ranks were similar. Body weight has been shown to be a predictor of eventual dominant status in some reports [81] but not others [Bastian, 2003No. 1810, suggesting that appreciably larger animals may elicit submissive responsiveness from smaller cage mates.…”

“…1810, suggesting that appreciably larger animals may elicit submissive responsiveness from smaller cage mates. One study [81] also found that greater reactivity to a novel environment predicted subordinate status. The significance of this observation for the present study is data showing thyroid hormones are lower in a number of affective disorders [82][83][84] and T3 can improve performance in novel, fear-evoking tasks by direct action on the hippocampus [85].…”

Dynamic body weight and body composition changes in response to subordination stress

“…Although the literature suggests that certain endocrine parameters, for example high plasma testosterone levels, may predispose an animal to express higher levels of aggression and become DOM, this is not universally the case. Likewise there is no effect of pre-grouping on the basis of the response to a dexamethasone challenge, plasma cortisol, or plasma testosterone in primates [40][41][42]. However, in the Common marmoset (Callithrix jacchus) cortisol concentrations in females prior to group formation are predictive of social status.…”

“…This body weight bias is also apparent in colony models where it can serve as a predicting factor in determining dominance [40]. Because of this, animals used in the VBS are typically weight-matched before the colony is formed such that no individual animal has a significant weight advantage thereby allowing us to consider other factors in determining dominance and subordination.…”

Memory of opponents is more potent than visual sign stimuli after social hierarchy has been established

“…Thus, while there are few changes in brain serotonergic activity following a second interaction with a familiar opponent, those that occur do not appear to be increases stimulated by a second stressful social interaction, but rather are represented by reductions in serotonergic activity, modulated by visual sign stimuli (raphé) and previous social status (hippocampal CA 3 ) respectively [39]. Dopaminergic activity is also influenced by social status and social interactions [3,17,32,51,84]. Dopaminergic activity in hippocampal nuclei of various vertebrate species has also been shown to be critical for spatial memory formation and retrieval [61,81].…”