Eyes on the future: buffering increased costs of incubation by abandoning offspring

Abstract Life history theory states that the resources invested in current reproduction must be traded off against resources needed for survival and future reproduction. Long-lived organisms have a higher residual reproductive value and are therefore expected to be sensitive to reproductive investments that may reduce survival and future reproduction. Individuals within a population may vary in phenotypic quality, experience, access to resources etc. This may affect their optimal reproductive investment level. In this study we manipulated reproductive costs by shortening and extending the incubation period in common eiders Somateria mollissima without altering clutch size. Females whose incubation time was prolonged experimentally, suffered higher mass loss and increased clutch loss/nest desertion. These females were also more prone to abandon their brood after hatching. Both clutch loss and brood abandonment decreased with clutch size in all treatment categories, indicating higher phenotypic quality and/or better access to resources for females producing more eggs. However, although females with prolonged incubation were lighter at hatching, their return rate and breeding performance in the following year were unaffected. These results show that individual quality as expressed through clutch size and body mass is affecting current reproductive investment level as well as future survival and breeding performance. The results also show that individual birds are sensitive to changes in their own condition, and when reproductive effort is approaching a level where survival or future survival may be compromised, they respond by terminating their current reproductive attempt.摘要 生活史理论（Life history theory）指出，用于当前繁殖活动的资源，必须与个体生存及未来繁殖所需的资源进行权衡。长寿生物拥有更高的剩余繁殖价值，因此预计其对可能降低生存能力与未来繁殖潜力的繁殖投入更为敏感。种群内的个体在表型质量、繁殖经验、资源获取渠道等方面存在差异，这会影响个体的最优繁殖投入水平。 本研究以普通绒鸭（Somateria mollissima）为研究对象，通过缩短或延长其孵化期且不改变窝卵数（clutch size）的方式，对繁殖成本开展实验操控。实验结果显示，孵化期被人为延长的雌性个体，出现了更显著的体重下降、更高的窝卵丢失率与弃巢率，且在雏鸟破壳后更易出现弃雏行为。在所有处理组别中，窝卵丢失与弃雏行为均随窝卵数的增加而减少，这表明产蛋量更高的雌性个体具备更高的表型质量，或拥有更优质的资源获取条件。 尽管孵化期延长的雌性个体在雏鸟孵化时体重更轻，但它们的越冬返回率与次年的繁殖表现并未受到显著影响。本研究结果表明，以窝卵数与体重所体现的个体质量，既会影响当前的繁殖投入水平，也会影响个体未来的生存能力与繁殖表现。同时，研究结果也证实，鸟类个体对自身身体状况的变化极为敏感：当繁殖投入接近可能损害当前或未来生存能力的临界水平时，它们会通过终止当前的繁殖尝试做出适应性应对。