Molecular phylogenetic analysis of dinoflagellate Scrippsiella trochoidea isolated from the East Asian waters

Previous studies found intraspecific diversity in Scrippsiella trochoidea A. R. Loeblich III, a widely distributed calcareous cyst-producing dinoflagellate. In this study, three strains (ST-1, ST-D6 and ST-K) of S. trochoidea isolated from the East Asian waters were studied, together with other geographical strains, to resolve their phylogenetic relationships. For the three East Asian isolates, two highly diverse regions of nuclear-encoded ribosomal DNA (rDNA), the 5.8S rDNA and its flanking internal transcribed spacers 1 and 2, and the 5′ portion of the large-subunit rDNA (encompassing the “D1“ and “D2” domains) were sequenced. Homologous sequences from other geographical isolates were selected from the GenBank database and the phylogenetic relationships were inferred from the molecular data of these strains. Strains of S. trochoidea were found to cluster into three major clades (STR1, STR2 and STR3), as reported in previous studies. Two of the three strains ST-1 and ST-K, were grouped in clade STR2, the other strain, ST-D6, belonged to clade STR3. The intraspecific diversity of S. trochoidea in East Asian waters makes it necessary to carry out phylogenetic investigations in combination with data of biogeography, population dynamics, and life cycle on the ecophysiology of a region.