Black Coating on New World Wolves Due to Genetic Mutation in Domestic Canines

A collaboration of scientists led by Gregory S. Barsh, a professor of pediatrics and genetics at the Stanford University School of Medicine, recently determined that the black coating on North American coyotes and wolves originated from a genetic mutation in domesticated dogs. This black coating, found mostly in the species inhabiting in the forests (as opposed to the tundra), signifies a rare moment in evolution where the genes from the domestic species became beneficial to the wild species.

Barsh and his colleagues have recently identified the mutated gene for the protein beta-defensin 3, which regulates pigmentation (or melanism) in domesticated dogs. Barsh and his laboratory have also discovered that the same mutation is responsible for the black coating in wolves and coyotes. According to their published paper in Science Express, the online edition of the journal Science, it was difficult to discern whether the mutation appeared first in the domesticated dogs in East Asia or in the Old World wolves; the exact time this mutation arose is still under question. Robert K. Wayne, an evolutionary biologist at the University of California Los Angeles and a co-author of the paper, said in an interview with the New York Times, "But even if it arose first in wolves, it was passed on to dogs who brought it to the New World and then passed it to wolves and coyotes soon after their arrival." Barsh and his laboratory have dated the first arrival of the domestic canines to around 14,000 years ago in Alaska and are currently looking for the gene mutation in any fossil remains in that region.

This evolutionary puzzle is of importance because, as the authors explained, cross-breeding between the wolf parent (with the wild type allele, or the most common phenotype in the population) and the dog parent (with the mutated allele) would result in offsprings with the heterozygous allele, or a mix between the two. Subsequent mating entirely within the wolf population should eventually erase the mutated gene. However, the gene is still present within the wolf population in the forests of North America. As the authors of the papers reported, this suggests the mutation is "positively selected," meaning that it is beneficial to the species for survival purposes and is therefore kept within the species. Although the immediate benefit from this positive selection is still not known, Barsh suggested in an interview with the New York Times that the protein beta-defensin 3 is involved in providing immunity against bacterial and viral skin infections which are more prevalent in the warmer forests than in the cooler tundra.

Marc Bekoff, a behavioral ethologist at the University of Colorado, argued that more evidence needs to be collected to confirm the adaptive advantages of the black coating, but did conclude in a statement to the New York Times that, "This is an important paper that among other things should make us revisit and likely revise what we mean by a pure' species."

Written by: Yangguang Ou

Edited by: Brittany Raffa and Renee Gilberti

Published by: Hoi See Tsao

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