Unexpected Genetic Diversity among and within Populations of the Toxic Dinoflagellate Alexandrium catenella as Revealed by Nuclear Microsatellite Markers

Abstract

Since 1998, blooms of Alexandrium catenella associated with paralytic shellfish poisoning have been repeatedly reported for Thau Lagoon (French Mediterranean coast). Based on data obtained for rRNA gene markers, it has been suggested that the strains involved could be closely related to the Japanese temperate Asian ribotype of the temperate Asian clade. In order to gain more insight into the origin of these organisms, we carried out a genetic analysis of 61 Mediterranean and 23 Japanese strains using both ribosomal and microsatellite markers. Whereas the phylogeny based on ribosomal markers tended to confirm the previous findings, the analysis of microsatellite sequences revealed an unexpected distinction between the French and Japanese populations. This analysis also highlighted great intraspecific diversity that was not detected with the classical rRNA gene markers. The Japanese strains are divided into two differentiated A. catenella lineages: the Sea of Japan lineage and the east coast lineage, which includes populations from the Inland Sea and the Pacific Ocean. A. catenella strains isolated from Thau Lagoon belong to another lineage. These findings indicate that microsatellite markers are probably better suited to investigations of the population genetics of this species that is distributed worldwide. Finally, application of the population genetics concepts available for macroorganisms could support new paradigms for speciation and migration in phytoplankton assemblages.

Limits to gene flow in a cosmopolitan marine planktonic diatom

“…Third, assuming that centers of origin show a higher genetic diversity than newly invaded areas (68), the highest microsatellite allelic richness and H e in Japan suggests that clade I has spread from the northwestern Pacific to other regions. A similar phylogeographic pattern, in which planktonic microorganisms have spread from a NW Pacific center has been suggested for the dinoflagellate Alexandrium catenella (26). The lowest allelic richness and H e in the northeastern Pacific may then be due to founder effects caused by recent range expansions.…”

“…To date, population genetic studies of high-dispersal organisms in the marine environment have largely focused on pelagic or benthic animals with planktonic larval stages (21)(22)(23)(24). Population genetic structuring of planktonic microorganisms has been much less explored due to difficulties with species delineation and lack of finescale genetic markers for these organisms (25)(26)(27)(28).…”

Gene Expression in Proliferating Cells of the Dinoflagellate Alexandrium catenella (Dinophyceae)

“…The A. catenella monoclonal strain ACT03 was isolated from Thau lagoon (French Mediterranean) during a bloom that occurred in 2003. According to its rDNA sequence (32), this strain belongs to group IV of the A. tamarense complex (31), formerly known as the "Temperate Asia" (TA) clade (43). The strain was maintained in a seawater culture medium (ESNW) enriched without silicate (20).…”

Alien species in the Mediterranean Sea by 2010. A contribution to the application of European Union’s Marine Strategy Framework Directive (MSFD). Part I. Spatial distribution

“…Apparently its range is expanding across the Mediterranean Sea, as it has been found recently on the Tunisian coast (TURKI & BALTI, 2007). On the other hand, more recent studies using alternative molecular tools have questioned the close relationships between Japanese and Mediterranean populations, and hence the identification of Japan as the source area of A. catenella (MASSERET et al, 2009).…”