The origin of natural selection is linked to environmental heterogeneity, which influences variation in relative fitness among phenotypes. However, individuals in wild populations are exposed to a plethora of biotic and abiotic environmental factors. Surprisingly, the relative influence of multiple environmental conditions on the relative fitness of phenotypes has rarely been tested in wild populations. Identifying the main selection agent(s) is crucial when the target phenotype is tightly linked to reproduction and when temporal variation in selection is expected to affect evolutionary responses. By using individual-based data from a 29-year study of a short-lived migratory songbird, the pied flycatcher (Ficedula hypoleuca), we studied the relative influence of 28 temperature- and precipitation-based factors at local and global scales on selection on breeding time (egg laying) at the phenotypic level. Selection, estimated using the number of recruits as a proxy for fitness, penalized late breeders. Minimum temperatures in April and May were the environmental drivers that best explained selection on laying date. In particular, there was negative directional selection on laying date mediated by minimum temperature in April, being strongest in cold years. In addition, nonlinear selection on laying date was influenced by minimum temperatures in May, with selection on laying date changing from null to negative as the breeding season progressed. The intensity of selection on late breeders increased when minimum temperatures in May were highest. Our results illustrate the complex influence of environmental factors on selection on laying date in wild bird populations. Despite minimum temperature in April being the only variable that changed over time, its increase did not induce a shift in laying date in the population. In this songbird population, stabilizing selection has led to a three-decade stasis in breeding time. We suggest that variation in the effects of multiple climatic variables on selection may constrain phenotypic change.

中文翻译：

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全球和当地气候条件驱动的波动选择导致候鸟繁殖时间停滞。

自然选择的起源与环境异质性有关，环境异质性会影响表型之间相对适合度的变化。然而，野生种群中的个体暴露于过多的生物和非生物环境因素。令人惊讶的是，很少在野生种群中测试多种环境条件对表型相对适应性的相对影响。当目标表型与繁殖紧密相关并且选择的时间变化预计会影响进化反应时，识别主要选择因子至关重要。通过使用对短命迁徙鸣禽（Ficedula hypoleuca）进行的 29 年研究的基于个体的数据，我们在表型水平研究了 28 个基于温度和降水的局部和全球尺度因素对繁殖时间（产卵）选择的相对影响。选择，使用新兵数量作为适应度的代理估计，惩罚晚育种者。4 月和 5 月的最低温度是最能解释产蛋日选择的环境驱动因素。尤其是4月最低气温介导的产蛋期负向选择，在寒冷年份最强。此外，产蛋日的非线性选择受 5 月最低气温的影响，随着繁殖季节的进行，产蛋日的选择从无效变为负值。当 5 月的最低气温最高时，晚育种的选择强度增加。我们的结果说明了环境因素对野生鸟类产蛋日期选择的复杂影响。尽管 4 月的最低温度是唯一随时间变化的变量，但其升高并未导致种群产蛋日期发生变化。在这个鸣禽种群中，稳定的选择导致繁殖时间停滞了三年。我们建议多个气候变量对选择的影响的变化可能会限制表型变化。