Rangewide responses to an extreme heat event in <em>Mimulus cardinalis</em>

Premise: Extreme events are an understudied aspect of ongoing anthropogenic climate change that could play a disproportionate role in the threat that rapid environmental shifts pose to natural populations. Methods: We exposed plants originating from seeds that were harvested before (ancestors) and after (descendants) multiple extreme heat events from six populations across the range of Mimulus cardinalis (Phyrmaceae) to a short‐term heat‐wave treatment in controlled growth chamber environments. We assessed physiological, performance, and functional responses (stomatal conductance, leaf temperature deficit, photosystem II efficiency, relative growth rate, specific leaf area, and leaf dry matter content) to the heat‐wave treatment, along with evolutionary responses (differences between ancestors and descendants) of M. cardinalis populations to the recent natural extreme heat event. Results: Plants in the heat‐wave treatment increased their overall performance, and the magnitude of increase was generally greatest among trailing‐edge populations. Despite limited overall trait differences between ancestors and descendants, there was some evidence of divergent evolutionary responses among regions to the natural extreme heat event. However, we did not find evidence of adaptive evolution that affected how M. cardinalis populations responded to the heat‐wave treatment. Conclusions: These results demonstrate that many M. cardinalis populations may reside in environments that are below their optimum average temperature, revealing potential resiliency to future warming. However, limited evolutionary responses in M. cardinalis to the recent extreme heat wave could still indicate potential for future vulnerability to extreme climate events of increased intensity, frequency, and duration.前提：极端事件是当前人为气候变化中尚未得到充分研究的领域，其在快速环境变化对自然种群构成的威胁中可能发挥不成比例的重要作用。 方法：本研究选取来自猩红沟酸浆（Mimulus cardinalis）、透骨草科（Phrymaceae）分布范围内6个种群的种子，分别采集自多次极端高温事件发生前（祖先种群）与发生后（后代种群），将其置于可控生长箱环境中接受短期热浪处理。本研究评估了该热浪处理下的生理、生长表现与功能响应指标，包括气孔导度、叶温亏缺、光系统II效率、相对生长速率、比叶面积以及叶干物质含量；同时还分析了猩红沟酸浆种群对近期自然极端高温事件的进化响应（即祖先与后代种群间的差异）。 结果：经热浪处理的植株整体生长表现有所提升，且这种提升幅度在种群分布后缘种群通常最为显著。尽管祖先与后代种群间的整体性状差异有限，但有证据表明不同区域的种群对自然极端高温事件存在分化的进化响应。然而，本研究未发现影响猩红沟酸浆种群对热浪处理响应的适应性进化证据。 结论：本研究结果表明，多数猩红沟酸浆种群所处的环境平均温度可能低于其适宜阈值，这揭示了其对未来气候变暖的潜在恢复力。但猩红沟酸浆种群对近期极端热浪的进化响应有限，这仍可能预示着其未来在强度、频率与持续时间均增加的极端气候事件面前存在脆弱性。