First observations on the phylogeny of the families Gammaridae, Crangonyctidae, Melitidae, Niphargidae, Megaluropidae and Oedicerotidae (Amphipoda, Crustacea), using small subunit rDNA gene sequences

This study examines amphipod phylogeny based on small subunit (18S) rDNA sequence data. Complete sequences of 25 species representing six families were used to test the phylogenetic information content of this gene for reconstruction of amphipod phylogeny. The alignment proved to be informative for most of the studied taxa. The monophyly of the families Gammaridae, Crangonyctidae, Niphargidae and Oedicerotidae is supported. The Melitidae are not monophyletic in the reconstructed topologies, but weak molecular evidence for the monophyly of this group could be observed in spectra of supporting positions. A close relationship of Gammaridae+Melitidae or Gammaridae+Crangonyctidae is not supported, rather there are supporting positions for the incompatible sister-group relationship (Gammaridae+Niphargidae) and (Crangonyctidae+Niphargidae). The molecular evidence is in favour of the latter relationship. The evolution of cephalothoracic apodemes is discussed in the light of other phylogenetic hypotheses resulting from molecular data.