Coping style and cortisol levels in infancy predict hair cortisol following new group formation in captive rhesus macaques (Macaca mulatta)

Social instability in primate groups has been used as a model to understand how social stress affects human populations. While it is well established that individual cercopithecines have different temperaments or personalities, little is known about how temperament mediates the experience of social instability in large, naturalistic groups. Here, we report findings from a study tracking a newly formed group of captive rhesus macaques (Macaca mulatta). We examine whether inter-individual differences in temperament during infancy affect physiological responses to new group formation years later, measured through hair cortisol 9 months after the group was formed. Our results show that early life measures of temperament characteristics predict later-life hypothalamic-pituitary-adrenal activity following new group formation, though not always in the directions we predicted. Individuals with higher blood cortisol concentrations in response to a novel stressor and lower blood cortisol concentrations following a Dexamethasone Suppression Test in infancy had lower hair cortisol values following new group formation later in life. Individuals characterized in infancy as more emotional or more active exhibited lower hair cortisol profiles 9 months after group formation. We suggest that these two temperament characteristics, emotionality and activity, may represent two different mechanisms leading to low hair cortisol values. That is, the physiological measure of low hair cortisol may have two different meanings depending on temperament characteristics of the individual. Our results demonstrate that temperament and physiological responsiveness measures in infancy can predict individual responses to a new group formation years later.