Improving the analysis of dinoflagellate phylogeny based on rDNA.

Phylogenetic studies of dinoflagellates are often conducted using rDNA sequences. In analyses to date, the monophyly of some of the major lineages of dinoflagellates remain to be demonstrated. There are several reasons for this uncertainty, one of which may be the use of models of evolution that may not closely fit the data. We constructed and examined alignments of SSU and partial LSU rRNA along with a concatenated alignment of the two molecules. The alignments showed several characteristics that may confound phylogeny reconstruction: paired helix (stem) regions that contain non-independently evolving sites, high levels of compositional heterogeneity among some of the sequences, high levels of incompatibility (homoplasy), and rate heterogeneity among sites. Taking into account these confounding factors, we analysed the data and found that the Gonyaulacales, a well-supported clade, may be the most recently diverged order. Other supported orders were, in the analysis based on SSU, the Suessiales and the Dinophysiales; however, the Gymnodiniales and Prorocentrales appeared to be polyphyletic. The Peridiniales without Heterocapsa species appeared as a monophyletic group in the analysis based on LSU; however, the support was low. The concatenated alignment did not provide a better phylogenetic resolution than the single gene alignments.