Coat color in wolves

March 6, 2009 • 11:08 am

by Greg Mayer

An alert reader has directed my attention to an interesting paper on coat color in wolves (abstract only without subscription) in today’s issue of Science by Tovi Anderson of Stanford and 14 colleagues from the US, Canada, Italy, and Sweden. Coat color in wolves is a polygenic trait affected by age, but Anderson and her colleagues show that black color in young wolves is associated with a 3 base-pair deletion in a gene called CBD103, and that there is a habitat correlation with the frequency of this color: black wolves live in the forests, gray (or white) wolves on the tundra.  This would be very interesting on its own, but Anderson et al. go further.  By careful phylogenetic analyses, they show that the gene for black color has entered North American wolves, and coyotes and Italian wolves as well, by hybridization with domestic dogs; and that the gene has been subject to recent positive natural selection (shown by low variability in the part of the chromosome immediately surrounding the gene, indicating what is known as a “selective sweep”).  Thus, a correlation between habitat and coat color that is suggestive of adaptation, is shown to be based on heritable variation undergoing natural selection.

The sort of combined field and lab study done by Anderson et al., using classical genetics (they have pedigrees of the wild wolves!), ecology, and now molecular genetics, is among the kind of work that first attracted me to evolutionary biology, and is known as ecological genetics. This field of study, pioneered by the great British geneticist E.B. Ford, was once characterized by the great American geneticist Dick Lewontin as carrying on the British “genteel upper-middle-class tradition of fascination with snails and butterflies”; I’m glad the fascination has moved to some of the colonies and beyond, and been extended to wolves, coyotes, and dogs.

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