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Molecular data and the evolutionary history of dinoflagellates Saldarriaga Echavarría, Juan Fernando

Abstract

New sequences of ribosomal and protein genes were combined with available morphological and paleontological data to produce a phylogenetic framework for dinoflagellates. The evolutionary history of some of the major morphological features of the group was then investigated in the light of that framework. Phylogenetic trees of dinoflagellates based on the small subunit ribosomal RNA gene (SSU) are generally poorly resolved but include many wellsupported clades, and while combined analyses of SSU and LSU (large subunit ribosomal RNA) improve the support for several nodes, they are still generally unsatisfactory. Protein-gene based trees lack the degree of species representation necessary for meaningful in-group phylogenetic analyses, but do provide important insights to the phylogenetic position of dinoflagellates as a whole and on the identity of their close relatives. Molecular data agree with paleontology in suggesting an early evolutionary radiation of the group, but whereas paleontological data include only taxa with fossilizable cysts, the new data examined here establish that this radiation event included all dinokaryotic lineages, including athecate forms. Plastids were lost and replaced many times in dinoflagellates, a situation entirely unique for this group. Histones could well have been lost earlier in the lineage than previously assumed. The closest relatives to the dinokaryotic dinoflagellates appear to be apicomplexans, Perkinsus and Parvilucifera, syndinians and Oxyrrhis. Gonyaulacales, Dinophysiales and an expanded Suessiales are all holophyletic orders, while Gymnodiniales, Blastodiniales and Phytodiniales as currently circumscribed are polyphyletic. Peridiniales is likely to be a paraphyletic taxon that probably gave rise to Dinophysiales and Prorocentrales, as well as to several groups of Gymnodiniales and Blastodiniales, and possibly also to Gonyaulacales.

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