A phylogeographical study of the toxic benthic dinoflagellate genus Ostreopsis Schmidt

摘要

Aim \udOstreopsis is a benthic and epiphytic dinoflagellate producing potent toxins widespread in tropical and warm temperate coastal areas world-wide. We tested the hypothesis that as it is benthic, it would show distinct biogeographical patterns in comparison with planktonic species. Here, we analyse sequence variability in ribosomal DNA markers to provide the first phylogeographical study of this toxic benthic dinoflagellate.\ud\udLocation Mediterranean Sea, Atlantic Ocean, Pacific Ocean.\ud\udMethods Ribosomal DNA sequence data from partial nuclear LSU (D1/D2 domains) and 5.8S genes and non-coding internal transcribed spacer (ITS) regions were obtained from 82 isolates of Ostreopsis species, collected at 26 localities throughout the world. Molecular sequence data were analysed using maximum parsimony, maximum likelihood and Bayesian methods for phylogenetic inference. A statistical parsimony network was obtained based on concatenated\udLSU and 5.8S rDNA–ITS region sequences of the Mediterranean/Atlantic\udOstreopsis cf. ovata isolates to infer haplotype distribution over their\udgeographical range. Light epifluorescence microscopy analyses were performed on cultured and field Ostreopsis material for taxonomic identification, while laboratory experiments for encystment induction were carried out on selected O. cf. ovata isolates. Toxin assays of Ostreopsis species isolates were carried out using the haemolytic-based method.\ud\udResults Analyses based on single and concatenated ribosomal genes gave substantially similar results. The rDNA phylogeny revealed different clades corresponding to different species within the genus Ostreopsis. In the species O. cf. ovata, different genetic lineages were correlated with macrogeographical distribution. A network of haplotypes inferred from the Atlantic and Mediterranean\udisolates of O. cf. ovata revealed that these two areas might host a single panmictic population. The Atlantic/Mediterranean population of O. cf. ovata was differentiated considerably from the Indo-Pacific populations. Other species of Ostreopsis were found, but they turned out to be restricted to just one of the two main warm-water oceanic basins, the Mediterranean/Atlantic and the Indo-Pacific.\ud\udMain conclusions Ostreopsis cf. ovata was found to be widely dispersed\udthroughout the coastal areas of tropical and some warm temperate seas. In the Atlantic/Mediterranean region it may constitute a panmictic population that is highly distinct from Indo-Pacific populations. Ostreopsis cf. siamensis was found only in the Mediterranean Sea, and strains identified as Ostreopsis lenticularis and\udOstreopsis labens were found only in the Indo-Pacific region.