Molecular phylogeny of the marine dinoflagellate genus Heterodinium (Dinophyceae)
Résumé
The dinoflagellate genus Heterodinium has unusual morphological characters such as a mid-ventral intercalary plate with a pore, a small plate in the left side of the dorsal epitheca, three antapical plates, and a well-developed anterior cingular list. We obtained the first SSU rDNA sequences from single cells of six species of Heterodinium from Mediterranean coastal and open waters. They included the type species H. scrippsii and H. rigdeniae and representatives of the other subgenera, Sphaerodinium (H. doma, H. milneri, H. globosum) and Platydinium (H. pavillardii). SSU rDNA phylogeny showed that Heterodinium spp. formed a well-supported monophyletic group (100% bootstrap support) composed of two subclades: one comprising H. doma, H. pavillardii, H. globosum and H. rigdeniae, and another comprising H. milneri and H. scrippsii. This whole heterodiniacean clade branched among the poorly resolved short-branching sequences of the lineage comprising groups of Gymnodiniales, Peridiniales, Dinophysales and Prorocentrales. The current classification into subgenera, and even into morphological groups, is not supported by the molecular data. In contrast to previous classifications, our SSU rDNA phylogeny suggests that the genus Heterodinium is divergent from the clade of Gonyaulacales. Accordingly, the supposed homology of pores and plate patterns of Heterodinium and gonyaulacoids may require revision. In Heterodinium, the first antapical and postcingular plates may be interpreted as sulcal plates, suggesting a more typical hypothecal tabulation (5''', 2 `'''). Our new data and analysis indicate that the systematic position of Heterodinium is uncertain at present.