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 in 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.
|Number of pages||13|
|Journal||Journal of Evolutionary Biology|
|State||Published - Apr 2018|
Bibliographical noteFunding Information:
This work was supported by NSF grant IOS 1257295 and IOS 1051890, the Florida State Agricultural Experiment Station, and the joint United Nations Food and Agriculture Organization/International Atomic Energy Agency (FAO/IAEA) Coordinated Research Project Dormancy Management to Enable Mass-rearing to D.A.H. N.M.T. was supported by a postdoctoral fellowship from the United States Department of Agriculture (Award # 2015-67012-22793). This is publication No. 18-03-013 of the Kentucky Agricultural Experiment Station and is published with the approval of the Director. This work is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, Hatch Project under 1010996. The authors thank Megan Laughrey, Emily Richter, Bailey Pierce, Chao Chen, Carey Roberts, Edwin Simpson and Jasmine James for assistance with fly rearing and phenotyping. We thank Ted Morgan’s lab at Kansas State University of supplying fly lines, and Jeff Leips (University of Maryland, Baltimore County) for generously providing longevity and fecundity data for the DGRP. We appreciate comments from two anonymous reviewers that improved the quality of the manuscript.
© 2018 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2018 European Society For Evolutionary Biology
- Drosophila melanogaster
- Genome Wide Association Study
- cold hardiness
- reaction norm
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics