Data from: Don't put all eggs in one nest - spread them and cut time at risk

In many egg-laying animals, some females spread their clutch among several nests. The fitness effects of this reproductive tactic are debated. Using mathematical modelling and field observations we analyse an unexplored benefit of egg spreading in brood parasitic and other breeding systems: reduced time at risk for offspring. If a clutch takes many days to lay until incubation and embryo development starts after the last egg, a parasitic female by spreading her eggs can reduce offspring time in the vulnerable nest, at risk of predation or other destruction. The model suggests that she can achieve much of this benefit already by spreading her eggs among a few nests, even if her total clutch is large. Field data from goldeneye ducks Bucephala clangula show that egg spreading enables a fecund female to lay a much larger than average clutch, without increasing offspring time at risk in a nest. This advantage increases with female condition (fecundity) and can markedly raise female reproductive success. These results help explain the puzzle of nesting parasites in some precocial birds, which lay eggs in the nests of other females before laying in their own nest. Risk reduction by egg spreading may also play a role in the evolution of other breeding systems, for instance some forms of polyandry with male parental care.

在诸多卵生动物类群中，部分雌性个体将其整窝卵分散至多个巢穴内。这种繁殖策略的适合度效应迄今仍存在学术争议。本研究借助数学建模与野外观测手段，剖析了巢寄生（brood parasitic）类繁殖系统及其他繁殖体系中，分散产卵尚未被揭示的一项核心优势：缩短子代所处的风险暴露时长。若某窝卵从产出到进入孵化阶段需耗时多日，且胚胎发育始于最后一枚卵产出之后，那么巢寄生雌性通过分散产卵，可降低子代在易被捕食或遭受其他破坏的巢穴内的停留时间。建模结果显示，即便雌性个体的总产卵量较大，仅需将卵分散至少量巢穴中，即可获取该项优势的绝大多数收益。来自鹊鸭（Bucephala clangula）的野外观测数据表明，分散产卵可让繁殖力较强的雌性个体产出远超种群平均水平的窝卵数，同时不会增加子代在单巢穴内的风险暴露时长。该优势随雌性个体的生理状态（繁殖力）提升而增强，并可显著提高雌性的繁殖成功率。上述研究结果有助于解释部分早成鸟类的巢寄生谜题：这类鸟类会先将卵产于其他雌性的巢穴中，之后再在自身巢穴内产卵。通过分散产卵以降低风险的策略，或许也在其他繁殖体系的演化进程中发挥作用，例如部分存在雄性育幼行为的一妻多夫制繁殖模式。