Evolving mutation rate advances invasion speed of sexual species

Many species are shifting their ranges in response to global climate change. The evolution of dispersal during range expansion increases invasion speed, provided that a species can adapt sufficiently fast to novel local conditions. Mutation rates can evolve too, under conditions that favor an increased rate of adaptation. However, evolution at the mutator gene has thus far been deemed of minor importance in sexual populations due to its dependence on genetic hitchhiking with a beneficial mutation at a gene under selection, and thus its sensitivity to recombination. Here we use an individual-based model to show that the mutator gene and the gene under selection can be effectively linked at the population level during invasion. This causes the evolutionary increase of mutation rates in sexual populations, even if they are not linked at the individual level. The observed evolution of mutation rate is adaptive and clearly advances range expansion both through its effect on the evolution of dispersal rate, and the evolution of local adaptation. In addition, we observe the evolution of mutation rates in a spatially stable population under strong directional selection, but not when we add variance to the mean selection pressure. By this we extend the existing theory on the evolution of mutation rates, which is generally thought to be limited to asexual populations, with possibly far-reaching consequences concerning invasiveness and the rate at which species can adapt to novel environmental conditions as experienced under global climate change.