Abstract
The alveolates are composed of three major lineages, the ciliates, dinoflagellates, and apicomplexans. Together these 'protist' taxa play key roles in primary production and ecology, as well as in illness of humans and other animals. The interface between the dinoflagellate and apicomplexan clades has been an area of recent discovery, blurring the distinction between these two clades. Moreover, phylogenetic analysis has yet to determine the position of basal dinoflagellate clades hence the deepest branches of the dinoflagellate tree currently remain unresolved. Large-scale mRNA sequencing was applied to 11 species of dinoflagellates, including strains of the syndinean genera Hematodinium and Amoebophrya, parasites of crustaceans and dinoflagellates, respectively, to optimize and update the dinoflagellate tree. From the transcriptome-scale data a total of 73 ribosomal protein-coding genes were selected for phylogeny. After individual gene orthology assessment, the genes were concatenated into a >15,000 amino acid alignment with 76 taxa from dinoflagellates, apicomplexans, ciliates, and the outgroup heterokonts. Overall the tree was well resolved and supported, when the data was subsampled with gblocks or constraint trees were tested with the approximately unbiased test. The deepest branches of the dinoflagellate tree can now be resolved with strong support, and provides a clearer view of the evolution of the distinctive traits of dinoflagellates.