Data from: Linear reaction norms of thermal limits in Drosophila: predictable plasticity in cold but not in heat tolerance

1. Thermal limits of ectotherms have been studied extensively and are believed to be evolutionary constrained, leaving ectotherms at risk under future climate change. Phenotypic plasticity may extend the thermal limits, but we lack detailed characterizations of thermal limit reaction norms as well as an understanding of the interspecific variation of these reaction norms.

2. Here we investigated the interspecific variation in phenotypic plasticity of thermal limits in 13 Drosophila species. We obtained high-resolution reaction norms for upper and lower thermal limits across the permissive developmental thermal range (12.5 – 30°C). The estimated phenotypes were then associated (while accounting for phylogeny) with climatic parameters from the species’ distributional range.

3. All species showed linear reaction norms for cold tolerance (CTmin) and heat tolerance (CTmax) across developmental acclimation temperatures. We observed strong beneficial cold acclimation to lower temperatures in all species. Conversely, the heat acclimation response was non-existent in some species, and decreasing or increasing with increasing developmental acclimation temperatures in other species. The degree of phenotypic plasticity of CTmin and CTmax was neither related to the basal thermal limits (trade-off hypothesis) nor to climatic parameters connected to latitudinal distributions (latitudinal hypothesis).

4. A substantial and linear developmental plasticity of lower thermal limits is a general characteristic of Drosophila species, which allows for straightforward application in species distribution models. In general, upper thermal limits also show linear norms of reaction, but their adaptive significance is limited and highly variable among species, making general predictions across species rather impossible.

5. High resolution estimates of norms of reaction of thermal limits can considerably increase our understanding of the capacity of ectotherms to acclimate to different thermal environments. However, our understanding of the environmental drivers of the evolution of phenotypic plasticity and thus of the interspecific differences remains ambiguous, potentially constrained by limited microclimate information.

1. 变温动物（ectotherm）的热极限已得到广泛研究，且被认为受进化约束，这使得变温动物在未来气候变化下面临风险。表型可塑性（phenotypic plasticity）或可拓展热极限，但目前我们仍缺乏对热极限反应规范（reaction norm）的精细刻画，以及对这些反应规范种间变异的认知。
2. 本研究针对13种果蝇（Drosophila），探究了其热极限表型可塑性的种间变异。我们在12.5–30℃的适宜发育温度范围内，获取了上下热极限的高分辨率反应规范。随后，在校正系统发育关系的前提下，将估算得到的表型与物种分布区的气候参数进行关联分析。
3. 所有物种在发育驯化温度梯度下，其冷耐受极限（CTmin）与热耐受极限（CTmax）均呈现线性反应规范。我们观察到，所有物种均能通过低温冷驯化获得显著的冷耐受增益。与之相反，部分物种完全未表现出热驯化响应，其余物种的热驯化响应则随发育驯化温度升高而呈现降低或升高的趋势。CTmin与CTmax的表型可塑性程度既与基础热极限无关（不符合权衡假说），也与纬度分布相关的气候参数无关联（不符合纬度假说）。
4. 下热极限存在显著且线性的发育可塑性，是果蝇属物种的普遍特征，这一特性可直接应用于物种分布模型（species distribution model）。总体而言，上热极限同样呈现线性反应规范，但其适应性意义有限，且物种间差异极大，因此难以开展跨物种的通用预测。
5. 热极限反应规范的高分辨率估算，可大幅提升我们对变温动物适应不同热环境能力的认知。然而，我们对表型可塑性进化的环境驱动因子，以及由此产生的种间差异的认知仍不明确，这一局限可能受限于微气候信息的匮乏。