Genetic lineages and postglacial colonization of grayling (Thymallus thymallus, Salmonidae) in Europe, as revealed by mitochondrial DNA analyses

In stark contrast to other species within the Salmonidae family, phylogeogr aphic information on European grayling, Thymallus thymallus, is virtually n onexistent. In this paper, we utilized mitochondrial DNA polymerase chain r eaction-restriction fragment length polymorphism (mtDNA PCR-RFLP) and seque nce variation to infer the postglacial dispersal routes of T. thymallus int o and within northern Europe, and to locate geographically, potential evolu tionarily distinct populations. Mitochondrial analyses revealed a total of 27 T. thymallus haplotypes which clustered into three distinct lineages. Av erage pairwise interlineage divergence was four and nine times higher than average intralineage divergence for RFLP and sequence data, respectively. T wo European grayling individuals from the easternmost sample in Russia exhi bited haplotypes more genetically diverged from any T. thymallus haplotype than T. arcticus haplotype, and suggested that hybridization/introgression zone of these two sister species may extend much further west than previous ly thought. Geographic division of the lineages was generally very clear wi th northern Europe comprising of two genetically differentiated areas: (i) Finland, Estonia and north-western Russia; and (ii) central Germany, Poland and western Fennoscandia. Average interpopulation divergence in North Euro pean T. thymallus was 10 times higher than that observed in a recent mtDNA study of North American T. arcticus. We conclude that (i) North European T. thymallus populations have survived dramatic Pleistocene temperature oscil lations and originate from ancient eastern and central European refugia; (i i) genetic divergence of population groups within northern Europe is substa ntial and geographically distinct; and (iii) the remainder of Europe harbou rs additional differentiated assemblages that likely descend from a Danubia n refugium. These findings should provide useful information for developing appropriate conservation strategies for European grayling and exemplify a case with a clear need for multinational co-operation for managing and cons erving biodiversity.