Predation risk can influence behaviour, reproductive investment and, ultimately, individuals’ fitness. In high-risk environments, females often reduce allocation to reproduction, which can affect offspring phenotype and breeding success. In cooperative breeders, helpers contribute to feed the offspring, and groups often live and forage together. Helpers can therefore improve reproductive success, but also influence breeders’ condition, stress levels and predation risk. Yet, whether helper presence can buffer the effects of predation risk on maternal reproductive allocation remains unstudied. Here, we used the cooperatively breeding sociable weaver Philetairus socius to test interactive effects of predation risk and breeding group size on maternal allocation to clutch size, egg mass, yolk mass, and yolk corticosterone. We increased perceived predation risk before egg laying using playbacks of the adults’ main predator, gabar goshawk (Micronisus gabar). We also tested interactive effects of group size and prenatal predator-playbacks on offspring hatching and fledging probability. Predator-exposed females laid eggs with 4% lighter yolks, but predator-calls’ exposure did not clearly affect clutch size, egg mass or egg corticosterone levels. Playback-treatment effects on yolk mass were independent of group size, suggesting that helpers’ presence did not mitigate predation risk effects on maternal allocation. Although predator-induced reductions in yolk mass may decrease nutrients’ availability to offspring, potentially affecting their survival, playback-treatment effects on hatching and fledging success were not evident. The interplay between helper presence and predator effects on maternal reproductive investment is still an overlooked area of life history and physiological evolutionary trade-offs that requires further studies.

中文翻译：

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合作繁殖和捕食风险对卵分配和繁殖产出的相互作用

捕食风险会影响行为、生殖投资，并最终影响个体的健康。在高风险环境中，雌性通常会减少繁殖分配，这可能会影响后代表型和繁殖成功。在合作饲养者中，助手们负责喂养后代，并且群体经常一起生活和觅食。因此，帮助者可以提高繁殖成功率，但也会影响繁殖者的状况、压力水平和捕食风险。然而，辅助者的存在是否可以缓冲捕食风险对母性生殖分配的影响仍有待研究。在这里，我们使用合作繁殖的群居织鸟 Philetairus socius 来测试捕食风险和繁殖群体规模对母产窝数、卵质量、卵黄质量和卵黄皮质酮分配的交互影响。我们通过回放成虫的主要捕食者加巴尔苍鹰（Micronisus gabar），增加了产卵前感知的捕食风险。我们还测试了群体规模和产前捕食者回放对后代孵化和羽翼丰满概率的交互影响。暴露于捕食者的雌性产下的蛋黄颜色较浅 4%，但暴露于捕食者的叫声并没有明显影响产卵量、卵质量或卵皮质酮水平。回放处理对卵黄质量的影响与群体大小无关，这表明助手的存在并不能减轻捕食风险对母体分配的影响。尽管捕食者引起的卵黄质量减少可能会降低后代的营养利用率，从而可能影响其生存，但回放处理对孵化和羽​​翼成功的影响并不明显。帮助者的存在和捕食者对母性生殖投资的影响之间的相互作用仍然是生命史和生理进化权衡中被忽视的领域，需要进一步研究。