Systematics, Biodiversity and Evolution of Plants

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Thursday September 22, 2022, 4 pm CEST


R. Wayne Litaker1 and Brittany Ott2*

Criteria for using rDNA sequences to define dinoflagellate species

1 CSS, Inc. Under Contract to National Oceanic and Atmospheric Administration (NOAA), National Ocean Service, National Centers for Coastal Ocean Science, Beaufort Laboratory, Beaufort, North Carolina, United States of America.
2 Joint Institute for Food Safety and Applied Nutrition (JIFSAN), University of Maryland—College Park, College Park, MD, United States of America, Cell Biology and Molecular Genetics, University of Maryland—College Park, College Park, MD, United States of America
* Currently at: Center for Food Safety and Applied Nutrition, Office of Food Additive Safety, Department of Science and Technology—College Park, College Park, MD, United States of America.


rDNA sequences have been used to successfully delineate species in numerous animal and plant lineages. For dinoflagellates, the degree to which rDNA-based phylogenies can be used to distinguish species is controversial with some researchers arguing single gene phylogenies are inadequate and that only multigene phylogenies can provide sufficiently strong molecular evidence for species boundaries. This study was consequently undertaken to (1) begin addressing the efficacy of rDNA versus multigene phylogenies to delineate dinoflagellate species, (2) to conduct an extensive literature survey encompassing 473 manuscripts representing 232 genera and 863 described species to quantify how well SSU, ITS/5.8S or 5’ LSU phylogenies successfully delineated morphologically defined dinoflagellate species, and (3) to determine if a defined scheme governing how to jointly weight morphological characters versus rDNA phylogenies when describing dinoflagellate species could be developed. To address these questions, we constructed transcriptomic libraries for nine Gambierdiscus species and downloaded previously published libraries for related species to determine how well the D1-D3 and ITS/5.8S rDNA gene regions versus multigene phylogenies delineate these species. Both the D1-D3 and ITS/5.8S phylogenies and the multigene phylogenies were found to identify Gambierdiscus and Alexandrium species equally well. Results from the literature survey showed joint D1-D3 rDNA and ITS phylogenies are capable of identifying 97% of described dinoflagellate species, including all the species currently belonging to the harmful algal bloom genera Alexandrium, Ostreopsis and Gambierdiscus. The results from objectives 1 and 2 were sufficient to construct a protocol for identifying when ITS/5.8S rDNA sequence data would take precedence over morphological features in describing new dinoflagellate species. The protocol addresses situations such as: a) when a new species is both morphologically and molecularly distinct from other known species; b) when a new species and closely related species are morphologically indistinguishable, but genetically distinct; and c) how to handle potentially cryptic species and cases where morphotypes are clearly distinct but have the same rDNA sequence. The protocol also addresses other molecular, morphological, and genetic approaches required to resolve species boundaries in the small minority of species where the D1-D3/ITS region phylogenies fail.