Data from: Workforce effects and the evolution of complex sociality in wild Damaraland mole-rats

Explaining the evolution of eusocial and cooperatively breeding societies demands that we understand the effects of workforce size on the reproductive success of breeders. This challenge has yet to be addressed in the family that arguably exhibits the most extreme outcomes of vertebrate social evolution, the African mole-rats (Bathyergidae), leaving the ultimate causes of their many unusual adaptations open to debate. Here we report, using a 14-year field study of wild Damaraland mole-rats, Fukomys damarensis, that workers appear to have strong but unusual effects on offspring. Groups with larger workforces exhibited substantially higher rates of offspring recruitment while maintaining high juvenile survival rates; relationships that may have favored the evolution of the delayed dispersal, cooperation, morphological specialization and unusual patterns of longevity that characterize such societies. Offspring reared by larger workforces also showed slower growth, however. That
reduced offspring growth in larger groups has also been documented under ad libitum food conditions in the laboratory raises the possibility that this reflects socially-induced growth restraint, rather than simple constraints on resource availability. Our findings shed new light on the evolution of complex sociality in this enigmatic clade and highlight further departures from the norms reported for other cooperative vertebrates.

要解释真社会性（eusocial）与合作繁殖社会的演化逻辑，我们亟需明晰群体工鼠规模对繁殖者繁殖成功率的影响。这一科学难题在脊椎动物社会演化中展现出最极端演化结果的类群——非洲鼹形鼠科（Bathyergidae）中仍未得到解决，致使其诸多异常适应性特征的根本成因至今仍存争议。本研究基于对野生达马拉兰鼹形鼠（Fukomys damarensis）长达14年的野外调查，发现工鼠对后代具有显著却反常的影响。工鼠规模更大的群体，其后代招募率显著更高，同时幼体存活率维持在较高水平；这种关联或推动了该类社会标志性的延迟扩散、合作行为、形态特化以及反常长寿模式的演化。但值得注意的是，由更大规模工鼠群体抚育的后代生长速度更慢。此前已有研究在实验室自由采食条件下记录到大群体中后代生长减缓的现象，这提示该效应并非单纯源于资源可获得性受限，而是社会因素诱导的生长抑制。本研究结果为这一神秘演化支的复杂社会性演化提供了新的视角，同时也进一步揭示了其与其他合作繁殖脊椎动物已有研究结论的显著差异。