| Summary: | The object of my study are amphipod crustaceans of the Southern Ocean, more particularly, the complex of genera Orchomene belonging to the superfamily Lysianassoidea. These genera play a very important role in these ecosystems, because they are mainly scavengers, so they feed on benthic carcasses and food falls, they are very abundant in the Southern Ocean, and many species are endemic. Many species of this group are also characterized by a wide distribution range, often circum-Antarctic, and they also cover a large bathymetric range. In this study we used a DNA barcoding approach, which consists of taking a short nucleotide fragment to identify species. For animals, the standard barcode marker is the mitochondrial gene COI. For this gene, intraspecific divergences are often one order of magnitude lower than interspecific divergences, and this is a way to differentiate species. We used this approach on our group in order to detect possible cryptic species, since, in the past it has already been shown that many so-called circum-Antarctic species are actually composed of several species with a restricted distribution. And this was particularly the case for benthic brooding crustacean species which are characterized to have low dispersal capacities. The results of the barcoding showed that in the majority of the studied species, a genetic homogeneity was found even among specimens from remote sampling sites, which is indicative of a possible circum-Antarctic distribution. However, due to a lack of samples from e.g. the East Antarctic there is still no complete evidence. In four species, we found genetic divergent lineages and thus possible cryptic taxa, confirmed by the morphology. The different genetic patterns observed in these orchomenid species might be explained by the evolutionary histories undergone by these species, or by their different dispersal and gene flow capacities. As a conclusion, the DNA barcoding method was effective for this group, and can provide a rapid and costeffective tool in the context of biodiversity surveys for monitoring and conservation efforts in this unique environment.
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