Literature analysis of how well rDNA sequence perform at delineating dinoflagellate species

Dinoflagellate harmful algal bloom species are traditionally defined using morphological characters. Molecular evidence, however, sometimes indicates that morphospecies differ from biological species. This has led to a reliance on molecular characteristics, primarily rDNAbased phylogenies, along with morphology, as a basis for defining new species. This approach assumes that divergence in rDNA or other selected genes consistently parallels speciation events, but this has not been systematically tested. Consequently, this study was undertaken to assess how often rDNA molecular phylogenies succeeded or failed to delineate dinoflagellate species. Specifically, SSU, D1-D3 LSU and ITS/5.8S phylogenies presented in 473 publications were reviewed to determine how well the rDNA phylogenies discriminated dinoflagellate species, including those in known HAB genera. A total of 863 described species representing 232 genera were assessed. Results showed the ITS/5.8S and D1-D3 LSU rDNA phylogenies (~1,850- 2,500 bp), in combination, can simultaneously (a) identifying 97% of all dinoflagellate species and (b) provide unique sequences useful for developing species-specific, quantitative molecular assays. Genera where species are well resolved using the ITS/5.8S plus D1-D3 genes include Alexandrium, Ostreopsis and Gambierdiscus. Based on the review of the publications, it was also possible to develop a system for determining how much weight to assign morphological versus molecular characters when describing new species. Utilizing this system can accelerate the description of new dinoflagellate HAB species and the subsequent assessment of their relative toxicities.