Genetic structure of the world's polar bear populations

We studied genetic structure in polar bear (Ursus maritimus) populations by typing a sample of 473 individuals spanning the species distribution at 16 highly Variable microsatellite loci. No genetic discontinuities were found that would be consistent with evolutionarily significant periods of isolat ion between groups. Direct comparison of movement data and genetic data fro m the Canadian Arctic revealed a highly significant correlation. Genetic da ta generally supported existing population (management unit) designations, although there were two cases where genetic data failed to differentiate be tween pairs of populations previously resolved by movement data. A sharp co ntrast was found between the minimal genetic structure observed among popul ations surrounding the polar basin and the presence of several marked genet ic discontinuities in the Canadian Arctic. The discontinuities in the Canad ian Arctic caused the appearance of four genetic clusters of polar bear pop ulations. These clusters vary in total estimated population size from 100 t o over 10 000, and the smallest may merit a relatively conservative managem ent strategy in consideration of its apparent isolation. We suggest that th e observed pattern of genetic discontinuities has developed in response to differences in the seasonal distribution and pattern of sea ice habitat and the effects of these differences on the distribution and abundance of seal s.