38th Annual Meeting of the Society for Invertebrate Pathology

The Microspora are an ancient and divergent group of parasites that infect all phyla. Current molecular phylogenetic analysis suggests that a major radiation of these parasites may have occurred in the crustacea and they are particularly common in amphipods with more than 20 novel species discovered from 18 host species. In studies of UK amphipods we have demonstrated that microsporidian parasites have great importance. In these systems vertical transmission is common and although parasites rarely cause gross pathology they exert a powerful influence on their hosts by disrupting sexual differentiation and causing sex ratio distortion. We have evidence that vertically transmitted microsporidia have been retained uring transcontinental invasion of their amphipod hosts and propose that parasitic sex ratio distortion may facilitate host invasion by increasing the reproductive rate of the invading host species. The impact of these parasites on host sex determination, population growth and stability, biological invasion and community structure within amphipods calls for a wider evaluation of their role in crustacean hosts.