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 o f any phocid seal species. An analysis of population structure in this species across its European range was made using 7 phocid derived mic rosatellites in a sample of 1,029 individuals from 12 separate geograp hic areas. Despite the species potential for long-distance movement, s ignificant genetic differentiation between areas was observed using an unbiased estimator of R-ST. Six distinct population units were identi fied: Ireland-Scotland, English east coast, Waddensea, western Scandin avia (Norway-Kattegat-Skagerrak-west Baltic), east Baltic, and Iceland . Little local substructuring is present along coastlines with a conti nuous distribution of breeding animals, but differentiation does incre ase with geographic distance. The degree of differentiation is greater over equivalent distances where the distribution is discontinuous, su ch as along coasts where breeding colonies are separated by large dist ances or by stretches of open sea. Patterns of population differentiat ion derived from microsatellites are very similar to those obtained fr om previous mitochondrial DNA analysis and suggest that philopatry in harbor seals operates over 300-500 km. In Europe, harbor seals have ex perienced a complex demographic history and patterns of population str ucture are likely to have been affected by natural environmental influ ences such as Pleistocene glaciations and epizootics. Comparison of Nm values from an unbiased estimator of R-ST, G(ST), and theta are consi stent and, in some cases, may indicate populations where conditions de viate from the expectations of the R-ST model.