Morphological and molecular systematics of unarmoured dinoflagellates (Gymnodiniales, Dinophyceae) from New Zealand

Abstract

The identification of species of the dinoflagellate genera Gymnodinium and Gyrodinium is difficult due to morphological character variability. However, several species of these genera produce brevetoxins or have caused biotoxin events. The discrimination of toxic from similar nontoxic species is consequently very important. The results from five different data sets were used to establish the phylogenetic relationships among species of the genera Gymnodinium and Gyrodinium from New Zealand. The tree topology representing the current classification of these genera was rejected following phylogenetic analysis. The separation of taxa into at least two main groups representing the G.breve-like and G.fuscumlike species is suggested from the results of this study. The position of Gymnodinium sanguineum and Gyrodiniuminstriatum relative to other species of the order Gymnodinialesrequires confirmation by the sequencing of different genes or ribosomal genes from similar taxa. Three new species, referred to in this thesis as Gymnodinium sp. 'papilionaceum', Gymnodinium sp. 'selliforme' and Gymnodinium sp. 'bidigitatum 'were more phylogenetically distinct than Gymnodinium breve and Gymnodinium mikimotoi, toxic species with which they were described on the basis of combined morphological and molecular data. The conservative morphological characters uniting the G. breve and G. mikimotoi-like taxa, were a linear apical groove, dorsoventral compression, left dorsolateral hypothecal pores, a smooth theca and the degree of extension of the sulcal groove onto the left epitheca The new species were also grouped with G.breve and G.mikimotoi on the basis of ultrastructural characters and pigment composition, and this work has extended the known range of species containing both fucoxanthin and/or derivatives and the rare pigment gyroxanthin-diester from four to eight. In contrast, the main carotenoid pigment in the G fuscum-like species was peridinin. The close phylogenetic relationship of Gymnodinium sp. 'papilionaceum', Gymnodinium sp. 'selliforme' and Gymnodinium sp. 'bidigitatum' to known toxic species and distinct from the type species for Gymnodinium, G.fuscum, suggested that a new genus should be erected for this group. The new species will be called Karenia papilionacea, Karenia selliformis, and Karenia bidigitata to reflect recent generic changes made by other scientists after this research was completed. The toxicity and global distribution of these three species must be investigated for the development of an appropriate biotoxin risk management strategy.