Data for: A large effect fitness trade-off across environments is explained by a single mutation affecting cold acclimation

<p>Identifying the genetic basis of local adaptation and fitness trade-offs across environments is a central goal of evolutionary biology. Cold acclimation is an adaptive plastic response for surviving seasonal freezing, and costs of acclimation may be a general mechanism for fitness trade-offs across environments in temperate zone species. Starting with locally adapted ecotypes of <em>Arabidopsis thaliana</em> from Italy and Sweden, we examined the fitness consequences of a naturally occurring functional polymorphism in <em>CBF2</em>. This gene encodes a transcription factor that is a major regulator of cold-acclimated freezing tolerance, and resides within a locus responsible for a genetic trade-off for long-term mean fitness. We estimated the consequences of alternate genotypes of <em>CBF2</em>on 5-year mean fitness and fitness components at the native field sites by comparing near isogenic lines with alternate genotypes of <em>CBF2</em> to their genetic background ecotypes. The effects of <em>CBF2</em> were validated at the nucleotide level using gene edited lines in the native genetic backgrounds grown in simulated parental environments. The foreign <em>CBF2</em> genotype in the local genetic background reduced long-term mean fitness in Sweden by more than 10%, primarily via effects on survival. In Italy, fitness was reduced by more than 20%, primarily via effects on fecundity. At both sites, the effects were temporally variable and much stronger in some years. The gene edited lines confirmed that <em>CBF2</em> encodes the causal variant underlying this genetic trade-off. Additionally, we demonstrated a substantial fitness cost of cold acclimation, which has broad implications for potential maladaptive responses to climate change. </p>