Genetic basis for adaptive melanism in North American wolves
In most mammals, two genes, Agouti and Mc1r, regulate the type, amount, and distribution patterns of these pigments, but in domestic dogs, there exists a third gene, Black (K), in which different alleles account for the black, brindled or fawn coat colors. Most wolves and coyotes have gray coats, but melanic morphs are found at high frequency in certain regions of North America. We found no mutations in Agouti or Mc1r that associated with melanistic coat color in wild canids. However, the ΔG23 mutation at the K locus (the same mutation responsible for black in dogs) is perfectly associated with melanism in both coyotes and wolves. In order to establish whether the K mutation occurred before the wolf/coyote/dog divergence or was introgressed from one species into another we studied the haplotype structure around the K locus. Our results indicate that Black (K) was introgressed multiple times from dogs into coyotes within the last 100 years. An introgression event from dogs also introduced the K allele into the North American wolf population where it was exposed to strong selective pressures, resulting in high frequencies of melanistic morphs in some regions. These results have important implications for the fields of molecular evolution and conservation biology, and lead to a better understanding of the molecular and historical basis for mutations that confer a selective advantage.