How the Gray Wolf Got Its Color

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Science  03 Jul 2009:
Vol. 325, Issue 5936, pp. 33-34
DOI: 10.1126/science.325_33

The Report “Molecular and evolutionary history of melanism in North American gray wolves” (T. M. Anderson et al., 6 March, p. 1339) suggests that the KB gene for black coat color was introgressed from dogs (Canis lupus familiaris) into North American gray wolves (C. lupus). However, the authors fail to consider an alternative hypothesis: The KB gene may have originated in the historic black wolves of eastern North America (C. niger, C. rufus, and C. lycaon).

The potential for gray wolf and eastern wolf introgressive hybridization (1) provides a mechanism to move an eastern wolf–derived variant into C. lupus during the Wisconsin glaciation (11,000 to 18,000 years ago). The only evidence for the KB gene in coyotes is in the range of the eastern wolf where hybridization between the two species (C. lycaon x latrans) has occurred (2) and not in more western geographies where gray wolves, dogs, and coyotes overlap. These coyote samples, however, were excluded from the analysis of the most recent common ancestor. If the selection hypothesis for black coat color in forested habitats is true, the prevalence of black pelage in the original timber wolves of the eastern temperate forests of Canada and the United States makes the inclusion of eastern wolf specimens critical for assessing the three possible evolutionary histories proposed by Anderson et al. We suggest that a more complete examination of black canids from eastern North America be conducted before conclusions of introgressive hybridization from dogs to gray wolves are drawn.


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