Cold survival and its molecular mechanisms in a locally adapted nematode population

Since Darwin, evolutionary biologists have sought to understand the drivers and mechanisms of natural trait diversity. The field advances toward this goal with the discovery of phenotypes that vary in the wild, their relationship to ecology, and their underlying genes. Here, we established resistance to extreme low temperature in the free-living nematode Caenorhabditis briggsae as an ecological and evolutionary model system. We found that C. briggsae strains of temperate origin were strikingly more cold-resistant than those isolated from tropical localities. Transcriptional profiling revealed expression patterns unique to the resistant temperate ecotype, including dozens of genes expressed at high levels even after multiple days of cold-induced physiological slowdown. Mutational analysis validated a role in cold resistance for seven such genes. As the temperate C. briggsae population likely diverged only ~700 years ago from tropical ancestors, our findings highlight a candidate case of very rapid, robust, and genetically complex adaptation, and shed light on the mechanisms at play.