Data from: The modulating role of group stability on fitness effects of group size is different in females and males of a communally rearing rodent

Group size may influence fitness benefits and costs that emerge from cooperative and competitive interactions in social species. However, evidence from plural breeding mammals indicates that group size is insufficient to explain variation in direct fitness, implying other attributes of social groups were overlooked.
We studied the natural population of a social rodent during 5 years to test the hypothesis that social stability – in terms of group composition – modulates the effects of increasing number of breeding females (a proxy of communal rearing) and males on the number of offspring weaned (sired) and on the number of offspring weaned (sired) surviving to breeding age (two proxies of direct fitness). We quantified the effects of social stability (measured as changes in female or male group members between mating and the onset of lactation) on these fitness measures.
We used live trapping, telemetry and DNA markers to determine social and fitness measures.
Social stability in degus was variable in terms of the number of changes in group composition across groups. Low stability was mostly due to mortality and emigration of group members.
Results supported a modulating role of social stability on the relationship between group size and the number of offspring weaned (sired). Stability in female and male group composition were both modulators of fitness to females and males.
The modulatory role of stability was sex specific, where high social stability was often fitness beneficial to the females. Instead, low social stability was fitness enhancing to the males.

社群物种因合作与竞争互动产生的适合度收益与成本，可能会受到群体规模的调控。然而，来自多雌繁殖（plural breeding）哺乳动物的研究证据表明，仅依靠群体规模无法解释直接适合度的变异，这意味着社会群体的其他特征此前被忽视了。
本研究针对一种社会性啮齿动物的自然种群开展了为期5年的野外调查，旨在验证如下假说：以群体组成界定的社会稳定性，可调节繁殖雌性（作为集体抚育（communal rearing）的替代指标）与雄性数量的增加，对雌性断奶后代、雄性父本后代的数量，以及上述两类后代存活至繁殖年龄的数量（二者均为直接适合度的替代指标）所产生的影响。本研究量化了社会稳定性——以交配期至泌乳起始阶段雌性或雄性群体成员的变化量为衡量标准——对上述适合度指标的作用。
本研究采用活捕技术、无线电遥测（telemetry）与DNA标记技术，获取社会群体特征与适合度相关数据。
八齿鼠（degu）的社会稳定性在不同群体间随群体组成变化量呈现显著差异。稳定性较低的情形，主要源于群体成员的死亡与迁出。
研究结果证实，社会稳定性对群体规模与断奶（父本）后代数量之间的关系具有调节作用。雌性与雄性群体组成的稳定性，均可分别调节雌性与雄性的适合度。
稳定性的调节作用具有性别特异性：较高的社会稳定性通常对雌性的适合度有利，而较低的社会稳定性则会提升雄性的适合度。