Elevated temperature increases genome-wide selection on de novo mutations

Adaptation in new environments depends on the amount and type of genetic variation available for evolution, and the efficacy by which natural selection discriminates among this variation to favour the survival of the fittest. However, whether some environments systematically reveal more genetic variation in fitness, or impose stronger selection pressures than others, is typically not known. Here, we apply enzyme kinetic theory to show that rising global temperatures are predicted to intensify natural selection systematically throughout the genome by increasing the effects of DNA sequence variation on protein stability. We tested this prediction by i) estimating temperature-dependent fitness effects of induced random mutations in seed beetles adapted to ancestral or warm temperature, and ii) calculating 100 paired selection estimates on mutations in benign versus stressful environments from a diverse set of unicellular and multicellular organisms. Environmental stress per se did not increase the mean strength of selection on de novo mutation, suggesting that the cost of adaptation does not generally increase in new environments to which the organism is maladapted. However, elevated temperature increased the mean strength of selection on genome-wide polymorphism, signified by increases in both mutation load and mutational variance at elevated temperature. The theoretical predictions and empirical data suggest that this increase may correspond to a doubling of genome-wide selection for a predicted 2-4 degrees climate warming scenario in ectothermic organism living at temperatures close to their thermal optimum. These results have important implications for global patterns of genetic diversity and the rate and repeatability of evolution under climate change.