Data from: Genetic variation in the shape of cold survival curves in a single fly population suggests potential for selection from climate variability

Temperature variation is one of the primary challenges facing ectotherms, and the ability to tolerate a range of thermal environments is critical for setting current and future species distributions. Low temperature is particularly challenging for ectotherms because winter conditions have strong latitudinal and temporal variation. Lower lethal temperature (LLT) is a common metric of cold tolerance used in studies of local adaptation and plasticity. Comparisons of LLT across groups typically assume parallel S-shaped survival curves, but genetic variation in the shape of survival vs. temperature curves has not been assessed. Here, we measured the ability of 36 lines of the Drosophila Genetic Reference Panel (DGRP) to survive a 1 h cold shock at seven ecologically relevant low temperatures (-1 to -7°C) to create a high resolution response curve for each genotype. We observed surprising variation both in the magnitude of survival and the shapes of the response curves, with the curves clustering into four distinct shapes. To encompass variation in the shapes of these survival curves, we developed a new cold tolerance metric, Cumulative Cold Tolerance (CCT). By comparing our survival data with climatological data, we propose that variation in the shapes of cold survival curves arose from weak selection pressure to survive intermediate subzero temperatures in this mid-latitude population of flies. Using publicly available genome sequence and transcript expression data for these lines, we identified several candidate genes associated with CCT, and using transgenic RNAi we confirmed a functional role for many of these genes.

温度波动是变温动物（ectotherms）面临的核心挑战之一，而耐受多样热环境的能力是决定物种当前及未来分布范围的关键因素。低温对变温动物而言尤为严苛，因为冬季气候存在显著的纬度与时间维度上的波动。低温致死温度（Lower Lethal Temperature, LLT）是当地适应与可塑性研究中衡量耐寒性的常用指标。过往跨类群的LLT比较研究通常默认存活曲线呈统一的S形，但存活-温度曲线形状的遗传变异尚未得到评估。本研究针对36个果蝇遗传参考面板（Drosophila Genetic Reference Panel, DGRP）品系，在7种具有生态学意义的低温（-1至-7℃）条件下开展1小时冷冲击实验，测定其存活能力，以此为每个基因型构建高分辨率响应曲线。我们观测到两类意外变异：不仅存活幅度存在差异，响应曲线的形状亦各不相同，这些曲线可聚类为四种截然不同的形状。为涵盖这些存活曲线的形状变异，我们开发了一种全新的耐寒性指标——累积耐寒性（Cumulative Cold Tolerance, CCT）。通过将存活数据与气候数据进行比对，我们提出：本研究中的中纬度果蝇种群，其冷存活曲线的形状变异源于针对中等亚零温度存活的弱选择压力。利用这些品系的公开基因组序列与转录组表达数据，我们鉴定出多个与CCT相关的候选基因，并通过转基因RNA干扰（RNA interference, RNAi）实验验证了其中多数基因的功能作用。