Molecular and Evolutionary History of Melanism in North American Gray Wolves

Abstract

Morphological diversity within closely related species is an essential aspect of evolution and adaptation. Mutations in the Melanocortin 1 receptor (Mc1r) gene contribute to pigmentary diversity in natural populations of fish, birds, and many mammals. However, melanism in the gray wolf, Canis lupus, is caused by a different melanocortin pathway component, the K locus, that encodes a beta-defensin protein that acts as an alternative ligand for Mc1r. We show that the melanistic K locus mutation in North American wolves derives from past hybridization with domestic dogs, has risen to high frequency in forested habitats, and exhibits a molecular signature of positive selection. The same mutation also causes melanism in the coyote, Canis latrans, and in Italian gray wolves, and hence our results demonstrate how traits selected in domesticated species can influence the morphological diversity of their wild relatives.

Artificial selection of the melanocortin receptor 1 gene in Chinese domestic pigs during domestication

“…MC1R has a vital role in melanogenesis, as melanocytes produce black/brown eumelanin with active MC1R and red/yellow pheomelanin without MC1R signalling (Robbins et al, 1993). Polymorphisms in MC1R have also been documented and associated with coat colour variance in many domestic species, such as dogs, chickens, cats and cattle (Klungland et al, 1995;Eizirik et al, 2003;Kerje et al, 2003;Anderson et al, 2009). In pigs, six MC1R alleles associated with different colour phenotypes have been reported (Giuffra et al, 2000;Kijas et al, 1998Kijas et al, , 2001).…”

Hybrid fitness, adaptation and evolutionary diversification: lessons learned from Louisiana Irises

“…For example, the complete genome sequence for domestic dogs allowed a recent description of adaptive trait introgression involving genes that control coat color. Alleles from domestic dogs, which caused darker pelage, have apparently introgressed into North American wolf populations (Anderson et al, 2009). The pattern of genetic variation detected in wolf populations falsified the hypothesis of neutral diffusion of coat color alleles from dogs, and instead, supported the hypothesis that the introgression involved positive selection for the resulting darker coats in the hybrid wolves (Anderson et al, 2009).…”

“…Alleles from domestic dogs, which caused darker pelage, have apparently introgressed into North American wolf populations (Anderson et al, 2009). The pattern of genetic variation detected in wolf populations falsified the hypothesis of neutral diffusion of coat color alleles from dogs, and instead, supported the hypothesis that the introgression involved positive selection for the resulting darker coats in the hybrid wolves (Anderson et al, 2009). Similarly, Fitzpatrick et al (2009) used single-nucleotide polymorphisms in a scan of the genomes of hybrid populations formed between native and introduced species of salamanders in North America (Ambystoma californiense and Ambystoma mavortium, respectively).…”

“…Many have debated what these estimates might mean with regard to the impact of genetic exchange on evolutionary pattern and process (Anderson, 1949;Anderson and Stebbins, 1954;Mayr, 1963;Lewontin and Birch, 1966;Grant, 1981;Barton and Hewitt, 1985;Arnold, 1992Arnold, , 1997Arnold, , 2006Arnold, , 2008Grant andGrant, 1992, 2010;Dowling and DeMarais, 1993;Rieseberg, 1997;Rieseberg et al, 2003;Seehausen, 2004;Seehausen et al, 2008;Anderson et al, 2009). Significantly, there are now numerous studies that have inferred a causal link between natural hybridization and adaptive evolution and/or diversification (Grant and Grant, 2002;Salzburger et al, 2002;Rieseberg et al, 2003;Seehausen, 2004;Schwarz et al, 2005;Martin et al, 2006;Anderson et al, 2009;Johnson et al, 2010).…”

“…The third hypothesis derives from the recognition that a majority of plant lineages have allopolyploid ancestry (that is, polyploid lineages formed through hybridization; Arnold (1997Arnold ( , 2006), as well as from the proliferation of studies (mainly involving animal complexes) that have detected past gene flow during speciation through the application of various algorithms (Wakeley and Hey, 1997;Templeton, 2001;Geneva and Garrigan, 2010;Wang and Hey, 2010) to genomic data sets (Salzburger et al, 2002;Seehausen, 2004;Won and Hey, 2005;Anderson et al, 2009;Green et al, 2010;Pinho and Hey, 2010; see also Arnold (2006Arnold ( , 2008 for a review of additional examples). Less frequently referred to are the literally thousands of studies documenting genetic exchange within groups of organisms as diverse as viruses, prokaryotes, plants and animals (see Grant and Grant (1992); Arnold (1997Arnold ( , 2006Arnold ( , 2008; Rieseberg (1997) and Seehausen (2004) for references to some of these studies).…”