Data from: Unpredictable perturbation reduces breeding propensity regardless of pre-laying reproductive readiness in a partial capital breeder

Theoretically, individuals of migratory species should optimize reproductive investment based on a combination of timing of and body condition at arrival on the breeding grounds. A minimum threshold body mass is required to initiate reproduction, and the timing of reaching this threshold is critical because of the trade-off between delaying breeding to gain in condition against the declining value of offspring with later reproductive timing. Long-lived species have the flexibility within their life history to skip reproduction in a given year if they are unable to achieve this theoretical mass threshold. Although the decision to breed or not is an important parameter influencing population dynamics, the mechanisms underlying this decision are poorly understood. Here, we mimicked an unpredictable environmental perturbation that induced a reduction in body mass of Arctic pre-breeding (before the laying period) female common eiders (Somateria mollissima; a long-lived migratory seaduck) while controlling for individual variation in the pre-laying physiological reproductive readiness via vitellogenin (VTG) - a yolk-targeted lipoprotein. Our aim was to causally determine the interaction between body condition and pre-laying reproductive readiness (VTG) on breeding propensity by experimentally reducing body mass in treatment females. We first demonstrated that arrival body condition was a key driver of breeding propensity. Secondly, we found treatment and VTG levels interacted to influence breeding propensity, indicating that our experimental manipulation, mimicking an unpredictable food shortage, reduced breeding propensity, regardless of the degree of pre-laying physiological reproductive readiness (i.e., timing of ovarian follicles recruitment). Our experiment demonstrates that momentary environmental perturbations during the pre-breeding period can strongly affect the decision to breed, a key parameter driving population dynamics.

从理论层面而言，迁徙物种的个体应结合抵达繁殖地的时机与身体状况，优化繁殖投入。启动繁殖需达到最低体质量阈值，而达成该阈值的时机至关重要——这是因为存在权衡关系：延迟繁殖以改善身体状况，与后代因繁殖时间延后而价值降低之间的取舍。长寿物种在其生活史中具备灵活性，若无法达到该理论体质量阈值，则可在特定年份跳过繁殖。尽管繁殖与否的决策是影响种群动态的关键参数，但该决策背后的机制仍有待深入阐明。本研究模拟了一种不可预测的环境扰动，该扰动导致北极地区繁殖前（产卵期前）的雌性普通绒鸭（Somateria mollissima，一种长寿的迁徙海鸭）体质量下降，同时通过卵黄蛋白原（vitellogenin, VTG）——一种靶向卵黄的脂蛋白——控制产卵前个体的生理繁殖准备度差异。本研究旨在通过对处理组雌性个体实施体质量降低的实验操作，因果性地明确身体状况与产卵前繁殖准备度（VTG水平）对繁殖倾向的交互作用。我们首先证实，抵达时的身体状况是繁殖倾向的关键驱动因素。其次，我们发现实验处理与VTG水平共同影响繁殖倾向，表明我们模拟不可预测食物短缺的实验操作降低了繁殖倾向，无论产卵前生理繁殖准备度（即卵巢卵泡募集时机）的程度如何。本实验证明，繁殖前期的短暂环境扰动可显著影响繁殖决策，而这正是驱动种群动态的关键参数。