Molecular evidence for further overlooked species within the Gammarus fossarum complex (Crustacea: Amphipoda)

The freshwater amphipod Gammarus fossarum Koch, in Panzer, 1836 is a locally abundant keystone species mainly occuring in European headwaters but also in larger rivers. Genetic studies in the past 25 years have revealed three cryptic species within nominal G. fossarum (types A, B and C). Assignments... Full description

The freshwater amphipod Gammarus fossarum Koch, in Panzer, 1836 is a locally abundant keystone species mainly occuring in European headwaters but also in larger rivers. Genetic studies in the past 25 years have revealed three cryptic species within nominal G. fossarum (types A, B and C). Assignments of specimens to these types were based on allozyme and 16 S markers. Today, a fragment of the cytochrome c oxidase subunit 1 ( CO 1) is primarily used as a genetic marker for species assignments (‘DNA Barcoding’), yet not a single CO 1 sequence of G. fossarum is available in the Barcode of Life Database. We analysed new CO 1 and 16 S data for German, Hungarian and Croatian G. fossarum specimens and compared them with 16 S and CO 1 sequences of G. fossarum from GenBank. Thereby, we close the gap between traditional allozyme- and 16 S -based species assignments and modern CO 1 barcoding. Studying genetic variation in 55 specimens from 29 populations, we identified between 11 and 23 novel and genetically distinct clades using distance- and tree-based methods. Our results suggest that G. fossarum comprises several additional, yet unrecognised, species in particular from the Balkan region. Therefore, a taxonomic revision and biogeographic reconsideration of the G. fossarum complex is urgently needed.