REVISED DINOFLAGELLATE PHYLOGENY INFERRED FROM MOLECULAR ANALYSIS OF LARGE-SUBUNIT RIBOSOMAL-RNA GENE-SEQUENCES

The nucleotide sequence analysis of the PCR products corresponding to the variable large-subunit rRNA domains D1, D2, D9, and D10 from ten r epresentative dinoflagellate species is reported. Species were selecte d among the main laboratory-grown dinoflagellate groups: Prorocentrale s, Gymnodiniales, and Peridiniales which comprise a variety of morphol ogical and ecological characteristics. The sequence alignments compris ing up to 1,000 nucleotides from all ten species were employed to anal yze the phylogenetic relationships among these dinoflagellates. Maximu m parsimony and neighbor-joining trees were inferred from the data gen erated and subsequently tested by bootstrapping. Both the D1/D2 and th e D9/D10 regions led to coherent trees in which the main class of dino flagellates, Dinophyceae, is divided in three groups: prorocentroid, g ymnodinioid, and peridinioid. An interesting outcome from the molecula r phylogeny obtained was the uncertain emergence of Prorocentrum lima. The molecular results reported agreed with morphological classificati ons within Peridiniales but not with those of Prorocentrales and Gymno diniales, Additionally, the sequence comparison analysis provided stro ng evidence to suggest that Alexandrium minutum and Alexandrium lusita nicum were synonymous species given the identical sequence they shared . Moreover, clone Gg1V, which was determined Gymnodinium catenatum bas ed on morphological criteria, would correspond to a new species of the genus Gymnodinium as its sequence clearly differed from that obtained in G. catenatum. The sequence of the amplified fragments was demonstr ated to be a valuable tool for phylogenetic and taxonomical analysis a mong these highly diversified species.