Maintaining differentiation without geographic isolation in the North American gray wolf

A common element of speciation models is geographic isolation. However, this requirement presents a problem for differentiation and related speciation of large carnivorous mammals that can disperse over long distances. The gray wolf is the most vagile terrestrial vertebrate species, and record dispersal events have been observed. Consequently, even widely separated populations are poorly differentiated. Wolves are generally described as territorial year-round. However, some populations of tundra and taiga-living wolves are reported to migrate over distances of hundreds of kilometres, and to be paler in coloration. Using satellite telemetry, we show that tundra wolves (n=19) follow barren ground caribou (n=19) on their 1500-kilometre annual migration. We also analysed genetics and coloration in tundra, taiga and boreal forest wolves (n=258, n=82 and n=64 respectively). Although tundra/taiga wolves overlap with forest conspecifics during the winter breeding season, they were differentiated from them and had Fst values of 0.30, 0.04, and 0.07 for mitochondrial, microsatellite and Y-chromosome markers (p<0.001 in all cases). Further, 93% of tundra/taiga wolves had a pale coloration whereas only 38% of forest wolves did (X2=85, p<0.0001). We suggest that specialization on migratory prey and selection for pale coloration in snow- covered habitats provide the basis for reproductive isolation. Tundra/taiga migratory and boreal forest territorial wolves are distinct but interconnected conservation entities. Hunting impacts on wolves may be substantial in areas where migratory and resident individuals congregate seasonally. Such impacts should be evaluated for the two ecotypes of wolves, and opportunities for migration should be maintained.