Genetic evidence for limited trans-Atlantic movements of the harbor porpoise Phocoena phocoena

In the North Atlantic, 14 regional subpopulations have been proposed for th e harbor porpoise Phocoena phocoena (Linnaeus, 1758). To what degree these populations experience genetic interchange is relatively unknown, particula rly on the larger scale of the North Atlantic as a whole. With the recent c ompletion of several regional genetic studies on population structure of th e harbor porpoise in the North Atlantic, came the opportunity to combine da tasets in an effort to broaden the geographic scope of focus. Three dataset s comprised of mitochondrial DNA control region sequences, representing the Northeast and Northwest Atlantic regions were pooled and reanalyzed to exa mine the degree of trans-Atlantic exchange among harbor porpoise population s, and to examine the evolutionary history of the species in the North Atla ntic. The movement of harbor porpoises across the Atlantic appears to occur at a low level. Genetic variability in the Northeast Atlantic is significa ntly lower than in the Northwest Atlantic, and may indicate a more recent r ecolonization for the Northeast Atlantic. The star phylogeny of northeaster n haplotypes, with a number of rare haplotypes closely related to the most abundant type, indicates a recent population expansion. A disjunction in ha plotypic frequencies between the Northeast and Northwest Atlantic probably occurs east of Greenland, but the exact location and source of the disjunct ion has yet to be determined.