Data from: An avian equivalent of selective abortion: post-laying clutch reduction under resource limitation

Selective elimination of excess offspring with poor fitness prospects may occur prenatally (selective abortion) or postnatally (brood reduction). Postnatal reduction is the dominant strategy, presumably because surplus progeny serves as a hedge against environmental and developmental uncertainty. In birds, its main proximate mechanism is asynchronous hatching, generating within-brood competitive asymmetry. Here, clutch-size reduction via last-egg abandonment was investigated in the asynchronously hatching red-necked grebe in a study area comprising two human-managed poorly predictable habitats with distinctly different food supplies. Last-egg abandonment, virtually absent in favorable food conditions, occurred regularly in larger clutches in conditions of brood-stage food scarcity. In the food-poor habitat, the production and body condition of fledglings did not differ between last-egg abandoning and caring pairs. The experimentally prolonged hatching interval increased the egg abandonment rate (irrespective of clutch size), but mainly in food-poor conditions. This is the first demonstration of parental clutch reduction in anticipation of brood-stage food limitation. Last-egg abandonment functions as an equivalent of abortion, as discarded offspring are excluded from the postnatal selection arena. This strategy might have evolved as 'best-of-a-bad-job' to reallocate parental resources when a strong mismatch between clutch size and chick survival probability reduced the hedging value of later-laid eggs.

针对适合度前景不佳的过剩后代实施选择性淘汰，可通过产前（选择性流产（selective abortion））或产后（窝雏削减（brood reduction））两种途径实现。产后窝雏削减是主流策略，推测其逻辑在于过剩子代可作为缓冲，抵消环境与发育不确定性带来的风险。在鸟类类群中，该策略的核心近因机制为异步孵化（asynchronous hatching），由此形成窝内竞争不对称性。本研究以具备异步孵化特性的红颈䴙䴘（red-necked grebe）为研究对象，在涵盖两处人工管理、可预测性较低且食物资源差异显著的生境的研究区域内，针对通过末卵遗弃（last-egg abandonment）实现窝卵数削减（clutch-size reduction）的现象展开了探究。末卵遗弃行为在食物条件充裕的环境中几乎不会出现，但在育雏期食物匮乏的情境下，该行为会在窝卵数较大的巢中频繁发生。在食物匮乏的生境中，实施末卵遗弃的亲鸟与抚育全部卵的亲鸟，其繁育的出飞幼鸟（fledglings）数量及身体状况均无显著差异。实验人为延长的孵化间隔可提升弃卵率（与窝卵数无关），但该效应主要出现在食物匮乏的生境中。本研究首次证实，亲鸟可预先响应育雏期食物匮乏的风险，主动实施窝卵数削减。末卵遗弃的作用等同于流产，因为被遗弃的后代会被排除在产后选择的筛选环节之外。当窝卵数与雏鸟存活概率间存在严重错配，导致晚产卵的缓冲价值下降时，该策略可能演化成为亲鸟重新分配繁殖资源的"best-of-a-bad-job"应对策略。