Natural selection and origin of a melanistic allele in North American Gray Wolves

Pigmentation is often used to understand hownatural selection affects genetic variation in wild populations since it can have a simple genetic basis, and can affect a variety of fitness-related traits (e.g., camouflage, thermoregulation, and sexual display). In graywolves, theKlocus, aβ-defensin gene, causes black coat color via a dominantly inherited K ^B allele.The allele is derived from dog-Wolf hybridization and is at high frequency in North American Wolf populations.We designed a DNA capture array to probe the geographic origin, age, andnumberof introgressionevents of the K ^B allele inapanel of 331wolves and20dogs.Wefound lowdiversity in K ^B , butnot ancestral ky,Wolfhaplotypes consistentwith a selective sweep of the black haplotype across North America. Further, North American Wolf K ^B haplotypes are monophyletic, suggesting that a single adaptive introgression from dogs to wolves most likely occurred in the Northwest Territories or Yukon. We use a new analytical approach to date the origin of the K ^B allele in Yukonwolves to between 1,598 and 7,248 years ago, suggesting that introgression with early Native American dogs was the source. Using population genetic simulations, we show that the K locus is undergoing natural selection in four Wolf populations. We find evidence for balancing selection, specifically in Yellowstonewolves, which could be a result of selection for enhanced immunity in response to distemper.With these data, we demonstrate how the spread of an adaptive variant may have occurred across a species' geographic range.