Social conflict and costs of cooperation in meerkats are reflected in measures of stress hormones

Measures of glucocorticoid stress hormones (e.g. cortisol) have often been used to characterize conflict between subordinates and dominants. In cooperative breeders where subordinates seldom breed in their natal group and assist in offspring rearing, increases in subordinate glucocorticoid levels may be caused by conflict among subordinates as well as by the energetic costs of helping behavior and fluctuations in food availability may exacerbate these effects. During a 6-year study of Kalahari meerkats (Suricata suricatta), we investigated how social, environmental, and individual characteristics influenced subordinate plasma cortisol levels. Subordinate females, who are often the target of aggression from dominant females, had higher cortisol levels when the dominant female in their group was pregnant while the cortisol levels of subordinate males were unaffected by the reproductive state of dominant females. Subordinates of both sexes had higher cortisol levels if they belonged to gro...