Esperk T, Kjaersgaard A, Walters R J, Berger D, Blanckenhorn W U
Department of Zoology, Institute of Ecology and Earth Sciences, University of Tartu, Tartu, Estonia.
Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland.
J Evol Biol. 2016 May;29(5):900-15. doi: 10.1111/jeb.12832. Epub 2016 Feb 9.
Extreme weather events such as heat waves are becoming more frequent and intense. Populations can cope with elevated heat stress by evolving higher basal heat tolerance (evolutionary response) and/or stronger induced heat tolerance (plastic response). However, there is ongoing debate about whether basal and induced heat tolerance are negatively correlated and whether adaptive potential in heat tolerance is sufficient under ongoing climate warming. To evaluate the evolutionary potential of basal and induced heat tolerance, we performed experimental evolution on a temperate source population of the dung fly Sepsis punctum. Offspring of flies adapted to three thermal selection regimes (Hot, Cold and Reference) were subjected to acute heat stress after having been exposed to either a hot-acclimation or non-acclimation pretreatment. As different traits may respond differently to temperature stress, several physiological and life history traits were assessed. Condition dependence of the response was evaluated by exposing juveniles to different levels of developmental (food restriction/rearing density) stress. Heat knockdown times were highest, whereas acclimation effects were lowest in the Hot selection regime, indicating a negative association between basal and induced heat tolerance. However, survival, adult longevity, fecundity and fertility did not show such a pattern. Acclimation had positive effects in heat-shocked flies, but in the absence of heat stress hot-acclimated flies had reduced life spans relative to non-acclimated ones, thereby revealing a potential cost of acclimation. Moreover, body size positively affected heat tolerance and unstressed individuals were less prone to heat stress than stressed flies, offering support for energetic costs associated with heat tolerance. Overall, our results indicate that heat tolerance of temperate insects can evolve under rising temperatures, but this response could be limited by a negative relationship between basal and induced thermotolerance, and may involve some but not other fitness-related traits.
热浪等极端天气事件正变得越来越频繁和强烈。种群可以通过进化出更高的基础耐热性（进化反应）和/或更强的诱导耐热性（可塑性反应）来应对升高的热应激。然而，关于基础耐热性和诱导耐热性是否呈负相关以及在持续的气候变暖下耐热性的适应潜力是否足够，目前仍存在争议。为了评估基础耐热性和诱导耐热性的进化潜力，我们对粪蝇脓蝇（Sepsis punctum）的一个温带源种群进行了实验进化。适应三种热选择 regime（热、冷和对照）的苍蝇后代在经历热驯化或非驯化预处理后，接受急性热应激。由于不同性状对温度应激的反应可能不同，因此评估了几个生理和生活史性状。通过将幼虫暴露于不同水平的发育（食物限制/饲养密度）应激来评估反应的条件依赖性。热击倒时间在热选择 regime 中最高，而驯化效应最低，这表明基础耐热性和诱导耐热性之间存在负相关。然而，存活率、成虫寿命、繁殖力和生育力并未表现出这种模式。驯化对热休克苍蝇有积极影响，但在没有热应激的情况下，热驯化苍蝇的寿命相对于未驯化苍蝇有所缩短，从而揭示了驯化的潜在成本。此外，体型对耐热性有积极影响，未受应激的个体比受应激的苍蝇更不容易受到热应激，这为与耐热性相关的能量成本提供了支持。总体而言，我们的结果表明，温带昆虫的耐热性可以在温度升高的情况下进化，但这种反应可能受到基础耐热性和诱导耐热性之间的负相关关系的限制，并且可能涉及一些但不是其他与适应性相关的性状。
