On the phylogeny of Lake Baikal amphipods in the light of mitochondrial and nuclear DNA sequence data

Two DNA sequence data sets, one from the nuclear 18S rRNA gene (520 bp long ), the other from the mitochondrial COI gene (540 bp), are used to characte rize the evolutionary history of the endemic Baikalian amphipod species ass emblage. The observed differentiation suggests that the initial radiation o f Baikalian lineages was ancient, probably older than the emergence of the initial large paleolake within the current lake basin in the mid-Tertiary. The mtDNA data suggest a principal division between the smooth fossorial ge nus Micruropus and the remaining Baikalian amphipod taxa included in the st udy. The monophyly of the Baikalian taxa with respect to the non-Baikalian Gammarus cannot be conclusively inferred from the mitochondrial sequences. The 18S rRNA data, however, suggest that the pelagic Baikalian species Macr ohectopus branickii is closer to the European Gammarus pulex than to any ot her gammarid studied, and give an indication of a polyphyletic origin of th e Baikalian amphipod fauna. Also, within the Baikalian assemblage, the majo r genera with strongly developed body armature, Acanthogammarus and Pallase a, may be polyphyletic.