MOLECULAR PHYLOGENY OF THE ACTIVE PACIFIC -OCEAN HYDROTHERMAL VENTS ALVINELLID POLYCHAETES

Phylogenetic trees were inferred by both distance and parsimony method s, using aligned sequences of the 28S rRNA 5'-end of 17 Polychaete spe cies. Aphelinidae is a monophyletic taxon among the Terebellomorpha wh ich 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 Alvine lla is longer in other Polychates (30 nucleotides more). This is expla ined by the insertions of groups of 3 to 11 nucleotides whose fixation probable did not change so much rRNA conformation. This fixation coul d have been promoted by the necessity of fast recolonizations of new a ctive hydrothermal vents (spatial isolation and ephemeral habitat). Th e comparison of the studied sequences of Polychates with those of coas tal 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 hydrothe rmal environment as recently hypothetized.