Multiple extreme climatic events strengthen selection for earlier breeding in a wild passerine

Global climate warming results in an increase in mean temperatures and in the frequency of extreme climatic events (ECEs), which could both strongly impact ecosystems and populations. Most studies assessing the impact of global warming on ecosystems have focused on warming trends while neglecting ECEs. In particular, the effects of multiple ECEs on fitness, and their consequences for selection, are still missing. Here we explored the effects of daily extreme rainfalls, as well as the occurrence of extremely hot and cold days, on clutch size and laying date in a wild blue tit population (Cyanistes caeruleus) monitored over 25 years. During the nestling phase (8–15 days old), the number of fledglings in a brood was negatively correlated with extremely hot days. The presence of extremely hot days between days 8 and 15 was also associated with an increase in the strength of selection acting on laying date, independently of mean temperature trends during the same period: when 10% of broods i...全球气候变暖导致平均气温升高与极端气候事件（extreme climatic events, ECEs）发生频率增加，二者均可对生态系统与种群造成强烈影响。当前多数评估全球变暖对生态系统影响的研究多聚焦于变暖趋势，却忽视了极端气候事件的作用。尤为关键的是，关于多重极端气候事件对适合度的影响，及其对自然选择作用的后续效应，目前仍鲜有研究。本研究以一项为期25年监测的野生蓝山雀（*Cyanistes caeruleus*）种群为研究对象，探究了每日极端降雨、极端高温日与极端低温日对窝卵数及产卵日期的影响。在雏鸟阶段（8~15日龄），一窝雏鸟的出飞幼鸟数量与极端高温日数呈负相关。同期（8至15日龄）出现的极端高温日，还会增强作用于产卵日期的自然选择强度，且该关联独立于同期的平均气温变化趋势：当10%的繁殖窝……