Behavioural, demographic and fitness consequences of social instability in cooperatively breeding dwarf mongoose groups

Social instability frequently arises in group-living species, but the potential costs have rarely been investigated in free-living cooperative breeders, especially across different timeframes. Using natural observations, body-mass measurements and life-history data from dwarf mongooses (Helogale parvula), we determined the short- and longer-term consequences of a change in one of the dominant breeding pair. We found that a new breeder led to alterations in both collective and individual behaviour (i.e., increases in communal scent-marking, engagement in intergroup interactions, sentinel activity and within-group grooming), as well as reduced body-mass gain, further demographic changes and decreased reproductive success (i.e., fewer pups surviving to adulthood). The effects were particularly apparent when it was the female breeder who changed; new female breeders were younger than more experienced counterparts. Our findings support the idea that stability and cooperation are strongly linked and provide potential reasons for previously documented health and fitness benefits of social stability.

群居物种中常出现社会不稳定现象，但针对自由生活的合作繁育者的潜在代价，相关研究却极少开展，尤其缺乏跨时间尺度的探讨。本研究以矮獴（Helogale parvula）的自然观察数据、体重测量结果与生活史资料为基础，探究了优势繁殖对其中一方更替所带来的短期与长期后果。研究发现，新繁殖者的出现会引发群体与个体行为的双重改变：具体表现为群体气味标记频次升高、参与群体间互动的频率增加、警戒行为增多以及群内理毛活动上升；同时还会导致体重增长减缓、种群结构进一步变化，以及繁殖成功率下降（即活到成年的幼崽数量减少）。当更替的是雌性繁殖者时，上述效应尤为显著；新上任的雌性繁殖者相较于经验更丰富的同类更为年轻。本研究结果支持“社会稳定性与合作行为紧密相关”这一观点，并为过往研究所记载的社会稳定性对健康与适应度带来的益处提供了潜在解释。