Studies of Arctic char Salvelinus alpinus (L.) in Transbaikalia: A Review of 25 Years of Research. Part 1. Distribution, Sympatric Forms, Morphology, Genetics
Authors:   Koltzov Institute of Developmental Biology RAS, Alekseev S. S. ,   A.N. Severtsov Institute of Ecology and Evolution RAS, Andreev R. S. ,   Irkutsk State University, Vokin A. I. ,   Irkutsk State University, Gordeeva N. V. ,   Vavilov Institute of General Genetics RAS, Korostelev N. B. ,   A.N. Severtsov Institute of Ecology and Evolution RAS, Matveev A. N. ,   Irkutsk State University, Pichugin M. Yu. ,   Lomonosov Moscow State University, Samusenok V. P. ,   Irkutsk State University, Samusenok I. V. ,   Irkutsk State University, Khlystov V. S. ,   Irkutsk State University, Yuriev A. L. ,   Irkutsk State University
Published: November 2022

In Transbaikalia, a much wider than previously believed, though mosaic distribution of Arctic charr has been documented over the last 25 years. We hypothesize that this species migrated to highland headwaters of the Lena drainage from the giant Lena-Vilui paleolake about 200–130 thousand years ago. After that it penetrated from the Lena (Vitim) basin to Lake Baikal basin across the Lena-Baikal watershed in the region of Lake Amut belonging to the Verkhnyaya Angara system. In the glacial epochs Arctic charr dwelled in large valley ice-dammed Vitim, Chara and Olekma lakes, which repeatedly emerged at the territory of Baikal mountain area and during interglacials moved to smaller cold-water high mountain lakes. Transbaikalia is one of the main centers of Arctic charr diversity and intensive speciation. The majority of present-day Transbaikalian populations are polymorphic being represented by two or three sympatric forms differing in adult size. Transbaikalian Arctic charr manifest high morphological interpopulational variability; the main direction of their morphological evolution underpinning their diversification is independent emergence of densely- and long-rakered forms in different lakes as the result of profound specialization to planktophagy. This diversification is also manifested in high-level differences of allopatric and sympatric forms in a number of meristic and morphometric characters. Transbaikalian charr have highly diverse mtDNA control region haplotypes of the Siberian subgroup of the Eurasian phylogenetic group. The data on mtDNA sequence variation evidence close relationship of Transbaikalian charr with Arctic charr of the Siberian subgroup from other parts of East Siberia and confirm their northern origin. The analysis of microsatellite variation shows genetic differentiation of sympatric forms; the level of this differentiation varies among form pairs from different lakes from medium to very high evidencing their reproductive isolation in some of the lakes. In nearly all cases sympatric and parapatric forms are genetically more similar with each other than with the forms from other lakes. The analysis of single nucleotide polymorphisms demonstrates similar results and also shows that parallel emergence of analogous charr forms (ecotypes) in different lakes has different genomic background. Still, as evidenced by transcriptome analysis, it proceeds due to similar changes in gene expression. Monophyletic clustering of Transbaikalian Arctic charr forms in phylogenetic trees according to the lakes and lake systems indicates independent origin of intralacustrine forms in different lakes by sympatric or parapatric speciation, although there are also arguments in favour of their secondary contacts.