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 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 groups 1) where neither of the dominant breeders in the group were their parents, 2) that contained a high proportion of subordinate females, or 3) 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 that both social conflict and cooperative behavior can elevate glucocorticoid levels in subordinates and that both effects can be modified by variation in weather and food availability.

糖皮质激素（glucocorticoid）应激激素的测定指标，例如皮质醇（cortisol），常被用于刻画从属个体与优势个体间的冲突。在从属个体极少在出生地群体中繁殖、且会协助抚育后代的合作繁育物种中，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，也可能源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效应。在针对喀拉哈里狐獴（Suricata suricatta）开展的为期6年的研究中，我们探究了社会、环境及个体特征对从属个体血浆皮质醇水平的影响。研究结果显示：从属雌性个体往往是优势雌性攻击的目标，当其所在群体的优势雌性处于孕期时，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。无论性别，从属个体若符合以下任一条件，其皮质醇水平均会升高：1）群体中的优势繁育者均非其亲生父母；2）群体中从属雌性占比偏高；3）群体规模要么极大要么极小，且这种差异在寒冷干燥的天气下尤为显著。此外，群体中存在幼崽的从属个体，其皮质醇水平也会升高。最后，无论性别，若从属个体相对于其年龄体型偏轻，或是在采样前一晚体重流失较少，其皮质醇水平也会更高。本研究表明，社会冲突与合作行为均可提升从属个体的糖皮质激素水平，且这两种效应均可因天气与食物可获得性的变化而发生改变。