Phylogénie moléculaire de polychètes Alvinellidae des sources hydrothermales actives de l'océan Pacifique

Phylogenetic trees were inferred by both distance and parsimony methods, using aligned sequences of the 28S rRNA 5'-end of 17 Polychaete species. Aphelinidae is a monophyletic taxon among the Terebellomorpha which also make a monophyletic group. Alvinella (2/2 species studied) is also a monophyletic taxon. The Paralvinella species (3/9 species) we studied cluster also in a monophyletic group. The D-1 domain of Alvinella is longer in other Polychates (30 nucleotides more). This is explained by the insertions of groups of 3 to 11 nucleotides whose fixation probable did not change so much rRNA conformation. This fixation could have been promoted by the necessity of fast recolonizations of new active hydrothermal vents (spatial isolation and ephemeral habitat). The comparison of the studied sequences of Polychates with those of coastal temperate and polar marine invertebrates shows that the relatively high Cytosine-Guanosine (C+G) level found in alvinellid sequences is not directly related to the particular characteristics of the hydrothermal environment as recently hypothetized.