Natural Selection and Origin of a Melanistic Allele in North American Gray Wolves

• Published in: Molecular Biology and Evolution
• Main Authors: Schweizer, Rena M, Durvasula, Arun, Smith, Joel, Vohr, Samuel H, Stahler, Daniel R, Galaverni, Marco, Thalmann, Olaf, Smith, Douglas W, Randi, Ettore, Ostrander, Elaine A, Green, Richard E, Lohmueller, Kirk E, Novembre, John, Wayne, Robert K
• Format: Text
• Language: English
• Published: Oxford University Press 2018
• Subjects: Discoveries; Northwest Territories; Yukon
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6455901/; http://www.ncbi.nlm.nih.gov/pubmed/29688543; https://doi.org/10.1093/molbev/msy031

Pigmentation is often used to understand how natural 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 gray wolves, the K locus, a β-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, and number of introgression events of the K(B) allele in a panel of 331 wolves and 20 dogs. We found low diversity in K(B), but not ancestral k(y), wolf haplotypes consistent with 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 Yukon wolves 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 Yellowstone wolves, 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.