Integrative taxonomy reveals a new Gammarus species (Crustacea, Amphipoda) surviving in a previously unknown southeast European glacial refugium

The multidisciplinarity of integrative taxonomy is particularly useful for clarifying the systematics of speciose groups that are poorly differentiated morphologically, and this approach can also illuminate their evolutionary history and biogeography. Here, we utilize it to examine the systematics and taxonomy of a newly recognized amphipod species, Gammarus hamaticornis n. sp., which belongs to a highly diverse genus of endemic freshwater crustaceans that show very limited morphological differentiation. Since this species is endemic to northern Dobrogea, a region at the northwestern Black Sea coast devoid of permafrost during the Last Glacial Maximum, we hypothesized that it survived insitu during the Quaternary climatic oscillations. We first examined the phylogenetic position of Gammarus hamaticornis n. sp. within the genus and then compared its morphology, phylogeography, distribution, and climatic niche with that of its sister species. Results indicate that G.hamaticornis n. sp. is most closely related to its widely distributed northern neighbor, G.kischineffensis, and a remarkable agreement was observed among morphological, multilocus coalescent and climatic analyses which supported the distinctiveness of both taxa. These apparently diverged during the Pliocene from a common ancestor that likely colonized freshwaters from the adjacent brackish basins of the shrinking Paratethys. The results indicate that G.hamaticornis n. sp. has persisted throughout the Pleistocene in northern Dobrogea, a hitherto hypothesized refugium confirmed for the first time with molecular genetic data. Due to its narrow geographical range, rarity in the local communities and highly fluctuating nature of the streams it inhabits, this species should be in the focus of future conservation priorities.