Mitochondrial phylogeny of notothenioids: A molecular approach to antarctic fish evolution and biogeography

Antarctic waters represent a unique marine environment delimited by an ocea nographic barrier, the Polar Front Zone, and characterized by constant subz ero temperatures and presence of sea ice. A group of teleost fish, the Noto thenioidei, have adapted to these challenging environmental conditions, und ergoing a remarkable diversification. In the present study a total of 798 b ase pairs, generated from partial sequencing of 16S and 12S mitochondrial r ibosomal RNA genes, were examined in 33 notothenioid species representative of all families included in the suborder Notothenioidei. Phylogenetic tree s, reconstructed on the basis of sequence data by different methods, indica te that traditional hypotheses on notothenioid systematics and biogeography might be in need of reexamination. Molecular evidence suggests that vicari ant speciation could be invoked to explain the early divergence of Eleginop s maclovinus, a species previously included in the family Nototheniidae, wh ich is now proposed as the closest sister group to all the rest of notothen ioids apart from bovichtids. On the other hand, repeated, independent dispe rsal through the Polar Front is proposed for the divergence of other subant arctic notothenioid species. Likewise, multiple, independent transitions fr om benthic to pelagic habit are inferred from molecular data, at variance w ith the more conservative hypothesis based on cladograms reconstructed from morphological data.