Data from: Early to rise, early to breed: a role for daily rhythms in seasonal reproduction

Vertebrates use environmental cues to time reproduction to optimal breeding conditions. Numerous laboratory studies have revealed that light experienced during a critical window of the circadian (daily) rhythm can influence reproductive physiology. However, whether these relationships observed in captivity hold true under natural conditions and how they relate to observed variation in timing of reproductive output remains largely unexplored. Here we test the hypothesis that individual variation in daily timing recorded in nature (i.e. chronotype) is linked with variation in timing of breeding. To address this hypothesis and its generality across species, we recorded incubation behavior data to identify individual patterns in daily onset of activity for 2 temperate-breeding songbird species, the dark-eyed junco (Junco hyemalis aikeni) and the great tit (Parus major). We found that females who first departed from their nest earlier in the morning (earlier chronotype) also initiated nests earlier in the year. Date of data collection and ambient temperature had no effect, but stage of incubation influenced daily onset of activity in great tits. Our findings suggest a role for daily rhythms as one mechanism underlying the observed variation in seasonal timing of breeding.

脊椎动物会依托环境信号，将繁殖时序调整至最优繁育条件。诸多实验室研究已证实，在昼夜节律（circadian rhythm）的关键窗口期内所经历的光照，会对繁殖生理机能产生影响。然而，这类在圈养环境中观测到的关联，在自然条件下是否依然成立，以及其与已观测到的繁殖产出时序变异之间的内在联系，迄今尚未得到充分探索。本研究旨在验证如下假说：野外记录的个体每日活动时序变异（即昼夜型（chronotype））与繁殖时序变异存在关联。为验证该假说及其跨物种普适性，我们针对两种温带繁殖鸣禽——暗眼灯草鹀（Junco hyemalis aikeni）与大山雀（Parus major）——记录其孵育行为数据，以识别个体每日活动起始的模式特征。研究结果显示：清晨率先离巢的雌性个体（即昼夜型更早的个体），其当年的筑巢起始时间也更早。数据采集日期与环境温度未对相关结果产生影响，但孵育阶段会影响大山雀的每日活动起始时间。本研究结果表明，昼夜节律是导致已观测到的繁殖季节时序变异的潜在机制之一。