GENETIC SUBDIVISIONS AMONG SMALL CANIDS: MITOCHONDRIAL DNA DIFFERENTIATION OF SWIFT, KIT, AND ARCTIC FOXES.

Gene flow can effectively suppress genetic divergence among widely separated populations in highly mobile species. However, the same may not be true of species that typically disperse over shorter distances. Using mtDNA restriction-site and sequence analyses, we evaluate the extent of divergence among populations of two small relatively sedentary North American canids, the kit and swift foxes (genus Vulpes). We determine the significance of genetic differentiation among populations separated by distance and those separated by discrete topographic barriers. Our results show the among-population component of genetic variation in kit and swift foxes is large and similar to that of small rodents with limited dispersal ability. In addition, we found two distinct groupings of genotypes, separated by the Rocky Mountains, corresponding to the traditional division between kit and swift fox populations. Previous workers have characterized these morphologically similar populations either as separate species or subspecies. Our mtDNA data also suggest that kit and swift fox populations hybridize over a limited geographic area. However, the sequence divergence between kit and swift foxes is similar to that between these taxa and the arctic fox (Alopex lagopus), a morphologically distinct species commonly placed in a separate genus. This result presents a dilemma for species concepts, and we conclude that kit and swift foxes should be recognized as separate species.