GENETIC-EVIDENCE FOR DIFFERENT MIGRATION ROUTES OF FRESH-WATER FISH INTO NORWAY REVEALED BY ANALYSIS OF CURRENT PERCH (PERCA-FLUVIATILIS) POPULATIONS IN SCANDINAVIA

To elucidate the colonization of freshwater fish into Norway following the last deglaciation of Europe 10 000 years ago, we have performed a survey using mitochondrial DNA variation (20 populations) and multilo cus DNA fingerprinting (14 populations) of the widely distributed perc h (Perca fluviatilis) from the Scandinavian peninsula and the Baltic S ea. Sequence analysis of a 378 bp segment of the perch mitochondrial c ontrol region (D-loop) revealed 12 different haplotypes. A nested clad e analysis was performed with the aim of separating population structu re and population history. This analysis revealed strong geographical structuring of the Scandinavian perch populations. In addition, the le vel of genetic diversity was shown to differ considerably among the va rious populations as measured by the bandsharing values (S-values) obt ained from multilocus DNA fingerprinting, with intrapopulation S-value s ranging from 0.19 in Sweden to 0.84 in the central part of Norway. A nalysis of the intrapopulation S-values, with S-value as a function of lake surface area and region, showed that these differences were sign ificant. The mitochondrial and DNA fingerprinting data both suggest th at the perch colonized Norway via two routes: one from the south follo wing the retreating glacier, and the other through Swedish river syste ms from the Baltic Sea area. Perch utilizing the southern route coloni zed the area surrounding Oslofjord and the lakes which shortly after d eglaciation were close to the sea. Fish migrating from the Baltic Sea seem to have reached no further than the east side of Oslofjord, where they presumably mixed with perch which had entered via the southern r oute. It seems likely that the migration events leading to the current distribution of perch also apply to other species of freshwater fish showing a similar distribution pattern.