Patterns of extensive genetic differentiation and variation among European harbor seals (Phoca vitulina vitulina) revealed using microsatellite DNA polymorphisms

The harbor seal (Phoca vitulina) has the most extensive distribution of anyphocid seal species. An analysis of population structure in this speciesacross its European range was made using 7 phocid derived microsatellitesin a sample of 1,029 individuals from 12 separate geographic areas. Despitethe species potential for long-distance movement, significant geneticdifferentiation between areas was observed using an unbiased estimator ofRST. Six distinct population units were identified: Ireland-Scotland,English east coast, Waddensea, western Scandinavia(Norway-Kattegat-Skagerrak-west Baltic), east Baltic, and Iceland. Littlelocal substructuring is present along coastlines with a continuousdistribution of breeding animals, but differentiation does increase withgeographic distance. The degree of differentiation is greater overequivalent distances where the distribution is discontinuous, such as alongcoasts where breeding colonies are separated by large distances or bystretches of open sea. Patterns of population differentiation derived frommicrosatellites are very similar to those obtained from previousmitochondrial DNA analysis and suggest that philopatry in harbor sealsoperates over 300-500 km. In Europe, harbor seals have experienced acomplex demographic history and patterns of population structure are likelyto have been affected by natural environmental influences such asPleistocene glaciations and epizootics. Comparison of Nm values from anunbiased estimator of RST, GST, and theta are consistent and, in somecases, may indicate populations where conditions deviate from theexpectations of the RST model.