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

Abstract

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 KB 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 KB allele inapanel of 331wolves and20dogs.Wefound lowdiversity in KB, butnot ancestral ky,Wolfhaplotypes consistentwith a selective sweep of the black haplotype across North America. Further, North American Wolf KB 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 KB 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.