Reinvestigation of Ostreopsis mascarenensis Quod (Dinophyceae, Gonyaulacales) from Réunion Island (SW Indian Ocean): molecular phylogeny and emended description

ABSTRACT

Ostreopsis mascarenensis is a toxic dinoflagellate described from the Indian Ocean based only on morphology, without molecular data. Morphological features of Ostreopsis have poor taxonomic value, and the addition of genetic data would ensure correct species identification. The present study reinvestigated field samples from Réunion Island and the western Indian Ocean to validate morphological and genetic data of O. mascarenensis from the type locality. A detailed morphological study used light, epifluorescence and scanning electron microscopy, and phylogeny was inferred from sequences of the LSU rDNA (D1–D3 and D8–D10 domains) and ITS–5.8S region obtained from isolated single cells. Morphology mostly agreed with the original description, but we highlight some features that were probably in error in the original description. SEM showed that the epitheca was conspicuously flattened while the hypotheca was convex, which had been previously interpreted as the opposite. Moreover, in contrast with the previous interpretation, the second apical plate was long and narrow, 1.6 to 2 times longer than the apical pore. Phylogenetic analyses showed that O. mascarenensis forms a new lineage among Ostreopsis species, confirming that it is well separated from all other species. Based on these analyses, O. mascarenensis appeared to be related to Ostreopsis fattorussoi and the undescribed species Ostreopsis sp. 3 and sp. 4, but the topologies were not well supported and these relationships remain unclear.

KEYWORDS:

• Dinoflagellates
• Epifluorescence
• Microscopy
• Phylogenetics
• Scanning electron microscopy
• Taxonomy

ACKNOWLEDGEMENTS

The authors thank Dr Cécile Jauzein for sharing unpublished data and for interesting discussions on the nature of the red bodies. The Regional Council of Brittany, the General Council of Finistère, and the urban community of Concarneau–Cornouaille–Agglomération are acknowledged for funding the Sigma 300 FE-SEM of the station of Marine Biology in Concarneau.

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Funding

This research received no specific grant from any funding agency, commercial or not-for-profit sector.