Predation risk affects the costs and benefits of prey life-history decisions. Predation threat is often higher during reproduction, especially in conspicuous colonial breeders. Therefore, predation may increase the survival cost of breeding, and reduce parental investment. The impact of predation risk on avian parental investment decisions may be hormonally mediated by prolactin and corticosterone, making them ideal tools for studying the trade-offs involved. Prolactin is thought to promote parental care and commitment in birds. Corticosterone is involved in allostasis and may either mediate reduced parental investment (corticosterone-fitness hypothesis), or promote parental investment through a reallocation of resources (corticosterone-adaptation hypothesis). Here, we used these hormonal proxies of incubation commitment to examine the impact of predation risk on reproduction in common eiders (Somateria mollissima) breeding in the Baltic Sea, and subject to high but variable predation pressure on adults and nests. We investigated baseline hormonal levels and hatching success as a function of individual quality attributes (breeding experience, female and duckling body condition), reproductive investment (clutch weight), and predation risk. We expected individuals nesting in riskier environments to reduce their parental investment in incubation, reflected in lower baseline prolactin levels and either higher (corticosterone-fitness hypothesis) or lower (corticosterone-adaptation hypothesis) baseline corticosterone levels. Contrary to our predictions, prolactin levels showed a positive correlation with nest predation risk. The unexpected positive relationship could result from the selective disappearance of low-quality females (presumably having low prolactin levels) from risky sites. Supporting this notion, female body condition and hatching success were positively correlated with predation risk on females, and baseline prolactin concentrations were positively correlated with duckling body condition, a proxy of maternal quality. In line with the corticosterone-adaptation hypothesis, baseline corticosterone levels increased with reproductive investment, and were negatively associated with nest predation risk. Hatching success was lower on islands where nest predation risk was higher, consistent with the idea of reduced reproductive investment under increased threat. Long-term individual-based studies are now needed to distinguish selection processes occurring at the population scale from individually plastic parental investment in relation to individual quality and variable predation risk.

中文翻译：

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孵化普通绒鸭（Somateria mollissima）的捕食威胁下的父母投资：荷尔蒙观点

捕食风险影响猎物生活史决策的成本和收益。繁殖期间捕食威胁通常更高，特别是在显眼的殖民地繁殖者中。因此，捕食可能会增加繁殖的生存成本，减少亲本投资。捕食风险对鸟类父母投资决策的影响可能是由催乳素和皮质酮激素介导的，这使它们成为研究相关权衡的理想工具。催乳素被认为可以促进鸟类的父母照顾和承诺。皮质酮参与动态平衡，可能会介导父母投资减少（皮质酮适应假说），或通过资源的重新分配（皮质酮适应假说）促进父母投资。这里，我们使用这些孵化承诺的荷尔蒙代理来检查捕食风险对波罗的海繁殖的普通绒鸭（Somateria mollissima）繁殖的影响，并受到对成虫和巢穴的高但可变的捕食压力的影响。我们调查了基线荷尔蒙水平和孵化成功与个体质量属性（繁殖经验、雌性和小鸭身体状况）、繁殖投资（离合器重量）和捕食风险的函数关系。我们预计在风险较高的环境中筑巢的个体会减少父母对孵化的投资，这反映在较低的基线催乳素水平和较高（皮质酮适应假设）或较低（皮质酮适应假设）基线皮质酮水平上。与我们的预测相反，催乳素水平与巢穴捕食风险呈正相关。出乎意料的正相关可能是由于低质量雌性（可能催乳素水平低）从危险地点的选择性消失造成的。支持这一观点，雌性身体状况和孵化成功与雌性捕食风险呈正相关，基线催乳素浓度与雏鸭身体状况呈正相关，这是母体质量的代表。与皮质酮适应假设一致，基线皮质酮水平随着生殖投资而增加，并且与巢捕食风险呈负相关。在巢穴捕食风险较高的岛屿上孵化成功率较低，这与在威胁增加的情况下减少繁殖投资的想法一致。