Mitochondrial DNA phylogeography of lake cisco (Coregonus artedi): evidence supporting extensive secondary contacts between two glacial races

The comparative molecular phylogeography of regional fish fauna has reveale d the wide distribution of young clades in freshwater fishes of formerly gl aciated areas as well as interspecific incongruences in their refugial orig ins and recolonization routes. In this study, we employed single-strand con formation polymorphism (SSCP) and sequence analyses to describe mitochondri al DNA (mtDNA) polymorphism among 27 populations of the lake cisco (Coregon us artedi) from its entire range of distribution in order to evaluate the h ypothesis of dual glacial refuges proposed by Bernatchez & Dodson against t he traditional view that this species is solely of Mississippian origin. Re sults indicate that this taxon is composed of two closely related groups th at are widely distributed and intermixed over most of the sampled range. Th e estimated level of divergence (0.48%), the contrast in the geographical d istribution of each group, as well. as the general distribution of C. arted i in North America together support the hypothesis that one group dispersed from a Mississippian refuge via the proglacial lakes, while the other is o f Atlantic origin and also took advantages of earlier dispersal routes towa rds eastern Hudson Bay drainages. However; the signal of past range fragmen tation revealed by a nested clade analysis was weak, and did not allow to f ormally exclude the hypothesis of a single Mississippian origin for both li neages. Comparisons with the phylogeographic patterns of other Nearctic fre shwater fishes suggest that the salinity tolerance and thermal sensitivity of lake cisco may have been determinant for its extensive postglacial dispe rsal. The presence or co-occurrence of sympatric or allopatric eco/morphoty pes were not found to be necessarily associated with the presence of both h aplotype groups.