Climate change affects organisms worldwide with profound ecological and evolutionary consequences, often increasing population extinction risk. Climatic factors can increase the strength, variability, or direction of natural selection on phenotypic traits, potentially driving adaptive evolution. Phenotypic plasticity in relation to temperature can allow organisms to maintain fitness in response to increasing temperatures, thereby “buying time” for subsequent genetic adaptation and promoting evolutionary rescue. Although many studies have shown that organisms respond plastically to increasing temperatures, it is unclear if such thermal plasticity is adaptive. Moreover, we know little about how natural and sexual selection operate on thermal reaction norms, reflecting such plasticity. Here, we investigate how natural and sexual selection shape phenotypic plasticity in two congeneric and phenotypically similar sympatric insect species. We show that the thermal optima for longevity and mating success differ, suggesting temperature-dependent trade-offs between survival and reproduction in both sexes. Males in these species have similar thermal reaction norm slopes but have diverged in baseline body temperature (intercepts), being higher for the more northern species. Natural selection favored reduced thermal reaction norm slopes at high ambient temperatures, suggesting that the current level of thermal plasticity is maladaptive in the context of anthropogenic climate change and that selection now promotes thermal canalization and robustness. Our results show that ectothermic animals also at high latitudes can suffer from overheating and challenge the common view of phenotypic plasticity as being beneficial in harsh and novel environments.

气候变化对世界范围内的生物造成深远的生态和进化影响，常常增加灭绝人口的风险。气候因素会增加表型性状自然选择的强度，变异性或方向，从而有可能推动适应性进化。与温度有关的表型可塑性可以使生物体适应不断升高的温度，从而保持适应性，从而为随后的基因适应和“进化拯救”“腾出时间”。尽管许多研究表明生物体对温度升高具有塑性反应，但尚不清楚这种热可塑性是否具有适应性。而且，我们对自然选择和性选择如何根据热反应规范运作的情况知之甚少，反映出这种可塑性。这里，我们调查自然和有性选择如何塑造两个同类和表型相似的同伴昆虫物种的表型可塑性。我们表明，长寿和交配成功的热最适方法不同，这表明在性别上生存和生殖之间的温度依赖性取舍。这些物种中的雄性具有相似的热反应范围，但基线体温（截距）有所不同，而北方物种则更高。自然选择有利于降低高温环境下的热反应范数斜率，这表明当前的可塑性在人为气候变化的背景下具有不良适应性，并且选择现在促进了热渠道化和稳健性。