Department of Biology, Indiana University, Bloomington, IN, USA.
Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA.
J Anim Ecol. 2022 Oct;91(10):1988-1998. doi: 10.1111/1365-2656.13772. Epub 2022 Jul 26.
Many species have shifted their breeding phenology in response to climate change. Identifying the magnitude of phenological shifts and whether climate-mediated selection drives these shifts is key for determining species' resilience to climate change. Birds are a strong model for studying phenological shifts due to numerous long-term research studies; however, generalities pertaining to drivers of phenological shifts will emerge only as we add study species that differ in life history and geography. We investigated 32 years of reproductive timing in a non-migratory population of dark-eyed juncos Junco hyemalis. We predicted that plasticity in reproductive timing would allow females to breed earlier in warmer springs. We also predicted that selection would favour earlier breeding and asked whether the temperatures throughout the breeding season would predict the strength of selection. To test these predictions, we examined temporal changes in the annual median date for reproductive onset (i.e. first egg date) and we used a sliding window analysis to identify spring temperatures driving these patterns. Next, we explored plasticity in reproductive timing and asked whether selection favoured earlier breeding. Lastly, we used a sliding window analysis to identify the time during the breeding season that temperature was most associated with selection favouring earlier breeding. First egg dates occurred earlier over time and strongly covaried with April temperatures. Furthermore, individual females that bred in at least 3 years typically bred earlier in warmer Aprils, exhibiting plastic responses to April temperature. We also found significant overall selection favouring earlier breeding (i.e. higher relative fitness with earlier first egg dates) and variation in selection for earlier breeding over time. However, temperature across diverse climatic windows did not predict the strength of selection. Our findings provide further evidence for the role of phenotypic plasticity in shifting phenology in response to earlier springs. We also provide evidence for the role of selection favouring earlier breeding, regardless of temperature, thus setting the stage for adaptive changes in female breeding phenology. We suggest for multi-brooded birds that advancing first egg dates likely increase the length of the breeding season, and therefore, reproductive success.
许多物种已经对气候变化做出了繁殖物候学的调整。确定物候学变化的幅度以及气候介导的选择是否驱动这些变化，是确定物种对气候变化适应能力的关键。鸟类是研究物候学变化的有力模式生物，因为有许多长期的研究；然而，只有当我们增加研究物种，这些物种在生活史和地理上有所不同时，关于物候学变化驱动因素的一般性结论才会出现。我们调查了一个非迁徙性的暗眼灯草雀 Junco hyemalis 种群 32 年的繁殖时间。我们预测，繁殖时间的可塑性将使雌性在温暖的春天更早地繁殖。我们还预测，选择将有利于更早的繁殖，并询问繁殖季节的整个温度是否可以预测选择的强度。为了检验这些预测，我们检查了年度繁殖开始的中位数日期（即第一枚蛋的日期）的时间变化，并使用滑动窗口分析来确定推动这些模式的春季温度。接下来，我们探讨了繁殖时间的可塑性，并询问选择是否有利于更早的繁殖。最后，我们使用滑动窗口分析来确定繁殖季节中与选择有利于更早繁殖最相关的温度。第一枚蛋的日期随着时间的推移而提前，与 4 月的温度密切相关。此外，至少在 3 年内繁殖的个体雌鸟通常在温暖的 4 月更早地繁殖，表现出对 4 月温度的可塑性反应。我们还发现了显著的整体选择有利于更早的繁殖（即更早的第一枚蛋日期具有更高的相对适合度），并且随着时间的推移，对更早繁殖的选择也有所不同。然而，不同气候窗口的温度并不能预测选择的强度。我们的研究结果进一步证明了表型可塑性在应对更早的春天而改变物候学方面的作用。我们还提供了证据表明选择有利于更早的繁殖，而与温度无关，从而为雌性繁殖物候学的适应性变化奠定了基础。我们建议对于多产卵的鸟类，提前第一枚蛋的日期可能会增加繁殖季节的长度，从而提高繁殖成功率。
