Data from: 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 behaviour 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 groups i) where neither of the dominant breeders in the group were their parents, ii) that contained a high proportion of subordinate females, or iii) that were either very large or very small, especially when the weather was cold and dry. Subordinates in groups containing young pups had higher cortisol levels. Finally, cortisol levels were higher in subordinates of both sexes if they were lighter for their age or had lost little body mass the night prior to sampling. Our results show how that both social conflict and cooperative behaviour can elevate glucocorticoid levels in subordinates and that both effects can be modified by variation in climate and food availability.

糖皮质激素应激激素（glucocorticoid stress hormones）的检测指标常被用于表征从属个体与优势个体之间的冲突。在合作繁育物种中，从属个体极少在出生群体内繁殖，且会协助抚育后代，从属个体糖皮质激素水平的升高，既可能源于从属个体间的冲突，也可能来自协助抚育行为带来的能量消耗，而食物可获得性的波动则会加剧这些影响。
在对卡拉哈里狐獴（Suricata suricatta）开展的6年研究中，我们探究了社会、环境及个体特征如何影响从属个体的血浆皮质醇（cortisol）水平。从属雌性个体常为优势雌性攻击的目标，当群体内的优势雌性处于妊娠状态时，从属雌性的皮质醇水平会升高；而从属雄性的皮质醇水平则不受优势雌性生殖状态的影响。
无论雌雄的从属个体，若处于以下三类群体中，其皮质醇水平均会升高：① 群体内的优势繁育者均非其亲生父母；② 群体内从属雌性占比过高；③ 群体规模过大或过小，且此类效应在寒冷干燥的天气下尤为显著。
处于有幼崽的群体中的从属个体，其皮质醇水平也会升高。
最后，无论雌雄的从属个体，若其体重相对于同龄个体偏轻，或是在采样前一晚的体重流失量较小，其皮质醇水平均会升高。
本研究结果表明，社会冲突与合作行为均可升高从属个体的糖皮质激素水平，且气候与食物可获得性的变化均可调控这两类效应。