Unraveling the diversity of a Baikal endemic amphipod: An integrative taxonomic study of Eulimnogammarus vittatus

Introduction

Cryptic diversity is common among crustaceans, including amphipods (Malacostraca: Amphipoda: Gammaroidea) of Lake Baikal, complicating their taxonomy. To test species hypotheses, an integrative taxonomy approach combining morphological, reproductive, and genetic data is recommended. This study focuses on the Eulimnogammarus vittatus species complex widely distributed throughout the lake. Previous studies identified two genetic lineages, southern (S) and western (W) with about 10% COI divergence (p-distance).

Methods

We genotyped 133 individuals from 25 locations across the lake and its outflow, the Angara River, using COI and 18S rRNA genes via Sanger sequencing. Patristic distances in COI were calculated according to Lefébure et al., 2006. Post- and pre-zygotic barriers between W and S lineages were assessed with laboratory experiments. Mate choice experiments (19 trials) tested pre-zygotic barriers, while post-zygotic barriers were assessed by no-choice crossing by monitoring survival, copulation, oviposition, and juvenile release over 180 days.

Results

We found that E. vittatus comprised three genetic lineages: W, S, and a novel northern (N). All samples from the southern basin of Lake Baikal belonged to the S lineage, while W and N were found in the central and northern basins. Mate choice trials showed clear preference for mates from their own lineage. Crossing experiments revealed juvenile release only in the control group. The maximum patristic distance (~0.18) was between W and S, while distances between these and the N lineage were 0.09, which is below the threshold value of 0.16 suggested for Gammaridae.

Conclusion

Reproductive barriers between the W and S lineages of E. vittatus confirm their status as separate species, whereas the N lineage appears to be compatible with W. Calculated patristic distances corroborate the observed reproductive barriers.

The work is supported by RScF (22-14-00128-P) and the Ministry of Science and Higher Education (FZZE-2024-0008).