Climatic oscillations during the Pleistocene epoch had a dramatic impact on the distribution of biota in the northern hemisphere. In order to trace glacial refugia and postglacial colonization routes on a global scale, we studied mitochondrial DNA sequence variation in a freshwater fish (burbot, Lota lota ; Teleostei, Gadidae) with a circumpolar distribution. The subdivision of burbot in the subspecies Lota lota lota (Eurasia...