Ultrastructure, phylogeny and histopathology of two novel haplosporidians parasitising amphipods, and importance of crustaceans as hosts

This study provides morphological, ultrastructural and phylogenetic characterization of 2 novel species of Haplosporidia (Haplosporidium echinogammari n. sp. and H. orchestiae n. sp.) infecting amphipods of the genera Echinogammarus and Orchestia collected in southwestern England. Both parasites infect the connective tissues associated with the digestive gland and the tegument, and eventually infect other organs causing disruption of host tissues with associated motor impairment and fitness reduction. Prevalence of infection varied with host species, provenance and season, being as high as 75% for individuals of E. marinus infected with H. echinogammari in June (n = 50). Although no spores were found in any of the infected amphipods examined (n = 82), the morphology of monokaryotic and dikaryotic unicellular stages of the parasites enabled differentiation between the 2 new species. Phylogenetic analysis of the new species based on the small subunit (SSU) rDNA gene placed H. echinogammari close to H. diporeiae in haplosporidian lineage C, and H. orchestiae in a novel branch within Haplosporidium. Genetic diversity of the haplosporidians infecting these and other amphipod species was evaluated and compared to morphological and ultrastructural changes to host tissues. The phylogenetic relationship of haplosporidian infections in other crustacean hosts is discussed after inclusion into the analysis of 25 novel SSU rDNA sequences obtained from crabs, isopods and crayfish.