Systematics, phylogeography and historical biogeography of Eusiroidea (Crustacea, Amphipoda) from the Southern Ocean, with a special focus on the families Epimeriidae and Iphimediidae

The physical isolation of the Antarctic shelf and extreme life conditions contribute to its high degree of endemism. The shelf fauna would, however, be composed of Gondwanan descendants, but also of more recent colonizers. Extreme temperature changes along the climatic history of this region led to the extinction of some lineages, while others flourished. Using molecular phylogenetic methods, this thesis aims to contribute to the general understanding of the evolutionary processes — extinctions, dispersals and in situ diversifications — shaping the biodiversity and geographical distributions of Antarctic amphipods of the families Epimeriidae (genus Epimeria) and Iphimediidae. The systematics of the superfamily presumably including the latter two model families, Eusiroidea, is first revised. Secondly, species boundaries within Epimeria are investigated by using a combination of DNA-based species delimitation methods and morphological descriptions, to ultimately reassess the geographical distribution of species. Finally, the origin of Antarctic lineages, dispersals in/out of the Antarctic shelf and in situ diversification patterns of both Epimeria and iphimediids are explored, using time-calibrated phylogenies. The systematic study of Eusiroidea indicates that at least species belonging to 14 families, including Epimeriidae and Iphimediidae, should be included in a phylogenetically meaningful delimitation of the superfamily. The species richness within Epimeria is greatly underestimated as most nominal species appear to be complexes of geographically-restricted pseudocryptic species. The monophyly of Antarctic Epimeria and (sub-)Antarctic iphimediids suggests that both lineages evolved in isolation since their origin. Both latter clades likely arose from late Gondwanan ancestors and diversified in a cooling environment.