Genetic structure of an amphipod species Eulimnogammarus (Philolimnogammarus) marituji Bazikalova, 1945 in the Lake Baikal basin

Hundreds of Baikal amphipod species form a so-called species flock, and Eulimnogammarus (Philolimnogammarus) marituji Bazikalova, 1945 is one of the most widespread representatives of this group in the southern part of Lake Baikal. Despite this, nothing is known about the genetic structure of this species. In this study, we identified three genetic lineages of E. marituji based on the sequences of a mitochondrial gene cytochrome c oxidase subunit I (COI) and a nuclear gene 18S rRNA. We designated these lineages as the southern (S), western (W) and central (C) lineages. While the three lineages are geographically separated in Baikal, they are mixed in the Angara and Yenisey rivers. The age of the last common ancestor is estimated at 3.6 million years ago. We also observed first-and second-generation hybrids, which at the moment prevents us from considering these lineages as separate biological species. In addition, based on the literature and our observations, we hypothesise that the previous findings of a distinct species Eulimnogammarus (Philolimnogammarus) viridis (Dybowsky, 1874) in the Yenisey River should be attributed to E. marituji.