Genetic diversity of the crustacean parasite Hematodinium (Alveolata, Syndinea)

In the absence of distinct morphological characteristics, knowledge of genetic relationships within and between protist parasite species is important for determining reservoir hosts and understanding the biology of the causative agents of emerging diseases. The genus Hematodinium is a member of Syndinea, an ubiquitous alveolate group found in all oceanic environments. Hematodinium parasites cause epizootics in crustaceans, yet their life cycle, genotypic variety and their phylogeny is poorly understood. By combining phylogenetic methods with analyses of secondary structures of variable ribosomal RNA genes we show that Hematodinium from the east and west North-Atlantic is comprised of distinct ribotypes or clades. These did not correspond to a specific area, but varied in host specificity. For example, a Hematodinium 'Langoustine' clade was only found in Nephrops norvegicus langoustines, whereas other clades were specific to crabs or seem to be generalist parasites.