Genetic and phenotypic diversity characterization of natural populations of the parasitoid Parvilucifera sinerae

Parasites exert important top-down control of their host populations. The host-parasite system formed by Alexandrium minutum (Dinophyceae) and Parvilucifera sinerae (Perkinsozoa) offers an opportunity to advance our knowledge of parasitism in planktonic communities. In this study, DNA extracted from 73 clonal strains of P. sinerae, from 10 different locations along the Atlantic and Mediterranean coasts, was used to genetically characterize this parasitoid at the species level. All strains showed identical sequences of the small and large subunits and internal transcribed spacer of the ribosomal RNA, as well as of the beta-tubulin genes. However, the phenotypical characterization showed variability in terms of host invasion, zoospore success, maturation time, half-maximal infection, and infection rate. This characterization grouped the strains within 3 phenotypic types distinguished by virulence traits. A particular virulence pattern could not be ascribed to host-cell bloom appearance or to the location or year of parasite-strain isolation; rather, some parasitoid strains from the same bloom significantly differed in their virulence traits. Identical markers such as ITS and beta-tubulin genes of P. sinerae strains from different geographic areas and from different years precludes their use in assessing intra-specific diversity and could indicate a recent dispersion of this species.