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

Gene flow can effectively suppress genetic divergence among widely sep arated populations in highly mobile species. However, the same may not be true of species that typically disperse over shorter distances. Us ing mtDNA restriction-site and sequence analyses, we evaluate the exte nt of divergence among populations of two small relatively sedentary N orth American canids, the kit and swift foxes (genus Vulpes). We deter mine the significance of genetic differentiation among populations sep arated by the distance and those separated by discrete topographic bar riers. Our results show the among-population component of genetic vari ation in kit and swift foxes is large and similar to that of small rod ents with limited dispersal ability. In addition, we found two distinc t groupings of genotypes, separated by the Rocky Mountains, correspond ing to the traditional division between kit and swift fox populations. Previous workers have characterized these morphologically similar pop ulations either as separate species or subspecies. Our mtDNA data also suggest that kit and swift fox populations hybridize over a limited g eographic area. However, the sequence divergence between kit and swift foxes is similar to that between these taxa and the arctic fox (Alope x lagopus), a morphologically distinct species commonly placed in a se parate genus. This result presents a dilemma for species concepts, and we conclude that kit and swift foxes should be recognized as separate species.