Data from: The oxidative costs of reproduction are group-size dependent in a wild cooperative breeder

Life-history theory assumes that reproduction entails a cost, and research on cooperatively breeding societies suggests that the cooperative sharing of workloads can reduce this cost. However, the physiological mechanisms that underpin both the costs of reproduction and the benefits of cooperation remain poorly understood. It has been hypothesised that reproductive costs may arise in part from oxidative stress, as reproductive investment may elevate exposure to reactive oxygen species, compromising survival and future reproduction and accelerating senescence. However, experimental evidence of oxidative costs of reproduction in the wild remains scarce. Here, we use a clutch-removal experiment to investigate the oxidative costs of reproduction in a wild cooperatively breeding bird, the white-browed sparrow weaver, Plocepasser mahali. Our results reveal costs of reproduction that are dependent on group size: relative to individuals in groups whose eggs were experimentally removed, individuals in groups that raised offspring experienced an associated cost (elevated oxidative damage and reduced body mass), but only if they were in small groups containing fewer or no helpers. Furthermore, during nestling provisioning, individuals that provisioned at higher rates showed greater within-individual declines in body mass and antioxidant protection. Our results provide rare experimental evidence that reproduction can negatively impact both oxidative status and body mass in the wild, and suggest that these costs can be mitigated in cooperative societies by the presence of additional helpers. These findings have implications for our understanding of the energetic and oxidative costs of reproduction, and the benefits of cooperation in animal societies.生活史理论（life-history theory）认为，繁殖必然伴随着代价；针对合作繁殖社群的研究表明，对繁殖工作量进行合作分担可降低此类代价。然而，支撑繁殖代价与合作收益的生理机制仍未得到充分阐明。已有假说提出，繁殖代价可能部分源于氧化应激（oxidative stress）：繁殖投入会提升个体暴露于活性氧（reactive oxygen species）的水平，进而损害存活能力与后续繁殖潜力，并加速衰老进程。然而，野外环境下繁殖的氧化代价相关实验证据仍较为匮乏。本研究通过移卵实验（clutch-removal experiment），针对野生合作繁殖鸟类白眉织布雀（Plocepasser mahali）开展繁殖氧化代价的相关研究。研究结果显示，繁殖代价受群体规模调控：与人工移除鸟卵的对照组个体相比，成功抚育后代的群体个体仅在小型群体（帮手数量较少或无帮手）中才会出现相应代价——表现为氧化损伤升高与体重降低。此外，在雏鸟育雏阶段，育雏频率更高的个体，其体重与抗氧化保护能力的个体内下降幅度更为显著。本研究结果提供了罕见的实验证据，证明野外环境中繁殖会对氧化状态与体重产生负面影响，同时表明合作繁殖社群中，额外帮手的存在可缓解此类繁殖代价。上述研究结果有助于我们深入理解繁殖的能量与氧化代价，以及动物社会中合作行为的收益。