Department of Evolution and Ecology, University of California, Davis, California, USA.
Department of Plant Biology, University of California, Davis, California, USA.
Ecology. 2024 Nov;105(11):e4423. doi: 10.1002/ecy.4423. Epub 2024 Sep 29.
The seasonal timing of life history transitions is often critical to fitness, and many organisms rely upon environmental cues to match life cycle events with favorable conditions. In plants, the timing of seed germination is mediated by seasonal cues such as rainfall and temperature. Variation in cue responses among species can reflect evolutionary processes and adaptation to local climate and can affect vulnerability to changing conditions. Indeed, climate change is altering the timing of precipitation, and germination responses to such change can have consequences for individual fitness, population dynamics, and species distributions. Here, we assessed responses to the seasonal timing of germination-triggering rains for eleven species spanning the Streptanthus/Caulanthus clade (Brassicaceae). To do so, we experimentally manipulated the onset date of rainfall events, measured effects on germination fraction, and evaluated whether responses were constrained by evolutionary relationships across the phylogeny. We then explored the possible consequences of these responses to contemporary shifts in precipitation timing. Germination fractions decreased with later onset of rains and cooler temperatures for all but three Caulanthus species. Species' germination responses to the timing of rainfall and seasonal temperatures were phylogenetically constrained, with Caulanthus species appearing less responsive. Further, four species are likely already experiencing significant decreases in germination fractions with observed climate change, which has shifted the timing of rainfall towards the cooler, winter months in California. Overall, our findings emphasize the sensitivity of germination to seasonal conditions, underscore the importance of interacting environmental cues, and highlight vulnerability to shifting precipitation patterns with climate change, particularly in more northern, mesic species.
生命史转折的季节性时机通常对适应性至关重要，许多生物依赖环境线索将生命周期事件与有利条件相匹配。在植物中，种子萌发的时间由降雨和温度等季节性线索来调节。物种间线索反应的变化可以反映进化过程和对当地气候的适应，并且可能会影响对变化条件的脆弱性。事实上，气候变化正在改变降水的时间，而对这种变化的萌发反应可能会对个体适应性、种群动态和物种分布产生影响。在这里，我们评估了十一种跨越 Streptanthus/Caulanthus 分支（十字花科）的物种对萌发触发降雨季节性时机的反应。为此，我们实验性地操纵了降雨事件的开始日期，测量了对萌发分数的影响，并评估了这些反应是否受到系统发育上的进化关系的限制。然后，我们探讨了这些反应对当代降水时间变化的可能后果。除了三个 Caulanthus 物种外，所有物种的萌发分数都随着降雨开始日期的推迟和温度的降低而降低。物种对降雨时间和季节性温度的萌发反应受到系统发育的限制，Caulanthus 物种的反应似乎不那么敏感。此外，由于气候变化已经将降雨时间推向了加利福尼亚州较冷的冬季月份，因此四个物种的萌发分数可能已经在经历显著下降。总的来说，我们的研究结果强调了萌发对季节性条件的敏感性，突出了相互作用的环境线索的重要性，并强调了在气候变化下，特别是在更北部、更湿润的物种中，对变化的降水模式的脆弱性。
