Introduction

Groups of closely related species are often sources of uncertainty in taxonomy. Lake Baikal amphipods (Crustacea: Amphipoda: Gammaroidea) are a perfect example. They comprise over 350 morphological species and subspecies, two conflicting taxonomies, and no comprehensive identification key. Here, we concentrate on conflicting views on the composition of the scavenger amphipods of the genus Ommatogammarus sensu Takhteew and try to resolve the conflict with molecular data.

Methods

We sequenced the standard barcode sequence, the mitochondrial cytochrome c oxidase subunit I 5’ fragment, as well as the 18S rRNA gene fragment as an additional barcode, in representatives of all subspecies. Three of them were analyzed for the first time. In addition, we performed low-coverage whole-genome sequencing for the three most abundant species and assembled full mitochondrial genomes for Ommatogammarus flavus, Ommatogammarus albinus, and Ommatogammarus carneolus melanophthalmus to obtain a time-calibrated phylogeny of the genus.

Results

The obtained phylogenies show that the last common ancestor of all species existed about 6 million years ago, and O. flavus sensu Takhteew (=Abludogammarus flavus sensu Kamaltynov) was the first to split from the rest of the species. Four O. carneolus subspecies sensu Takhteew (= three Pretiositus species + Eulimnogammarus hyacinthinus according to Kamaltynov) were close but formed two clusters of related sequences instead of four, while the sequences of 18S fragments were identical between these clusters.

Conclusions

The genus Ommatogammarus sensu Takhteew contains at least three clearly separated species. The relationship within O. carneolus containing two lineages needs further investigation, but at the moment, we do not have conclusive evidence to recommend splitting this species complex. Importantly, the reassignment of O. hyacinthinus to the genus Eulimnogammarus is not supported by molecular data.