Phylogenetic Relationships among Palearctic and Nearctic Whitefish (Coregonus sp.) Populations as Revealed by Mitochondrial DNA Variation

We recently documented the existence of two highly distinct mitochondrial DNA (mtDNA) phylogenetic groups of Coregonus sp. in Beringia in the absence of geographic separation. To test whether this resulted from secondary intergradation of two groups that evolved in allopatry in Eurasia and Beringia, mtDNA restriction-fragment-length polymorphisms of 210 whitefish representing 22 populations from Europe and Siberia were compared with mtDNA variation observed among 581 fish from North America. Results confirmed that Beringia represents a zone of secondary contact among endemic whitefish and a group of Eurasian origin. All Beringian populations clustered much more closely to Eurasian populations than other North American ones. We also compared mtDNA variation among Palearctic populations with that observed in North America. European populations clustered into two major mtDNA groups that exhibited a strong geographic pattern of distribution, independent of the morphological variation observed among populations: one dominated all the more northern populations and extended to Alaska–Yukon; the second largely dominated samples from central alpine lakes, and was absent from Beringia. These results suggest that central alpine lakes and northern Europe were postglacially recolonized by two genetically distinct white-fish groups that most likely evolved in allopatry followed by limited intergradation.