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 cluste...