Secondary contact between two divergent lineages of grayling Thymallus in the lower Enisey basin and its taxonomic implications

A contact zone between two widespread divergent lineages of grayling Thymallus sp. has been identified in the lower Enisey basin (Khantaiskoye Lake) in north central Siberia (Russia). Sequences of the mitochondrial DNA control region revealed two lineages with 2·6% divergence. Haplotypes from these two lineages clearly fall within two previously described clades, one presumably corresponding to Arctic grayling Thymallus arcticus found throughout the Siberian coastal zone as well as North America, and the other corresponding to grayling found elsewhere in the Enisey basin, including Lake Baikal and its tributaries. Allelic variation at seven microsatellite loci strongly suggests reproductive isolation in sympatry between these two lineages in Khantaiskoye Lake. Integration of these new data with existing knowledge on Thymallus throughout its Siberian range supports a taxonomic revision. The currently recognized sub‐specific lineages of Arctic grayling along the Siberian Arctic coast as well as grayling from North America should probably be regarded as T. arcticus . Arctic grayling, however, are limited to the coastal zone and lower reaches of the Enisey. Most of the Enisey basin, including Lake Baikal and its tributaries are occupied by another taxon, which should be recognized as Thymallus baicalensis . This perspective strictly follows evolutionary principles, eliminates the use of four sub‐specific names and circumvents the illogical mosaic distribution of T. arcticus arcticus , which nevertheless does not represent a monophyletic lineage.