Reservoirs for Parasitic Protists in Littoral Environments
Supervisor: Stephen W. Feist (CEFAS, UK)
The crustacean order Amphipoda comprises more than 9.500 species from marine, freshwater and even terrestrial environments. Ecologically their presence is of paramount importance in the energy flow from primary production to higher levels of the trophic chain. Their extraordinary abundance (up to 10.000 individuals per m2) and detritus feeding strategies makes them ideal reservoirs for several protistan parasites. The amphipods surveyed in this experiment were collected at different times from a little rocky cove in the English Channel (Weymouth; 50° 36´ 15´´N, 2° 26´ 59´´). Although eight different species of amphipods were identified, only two were abundant enough to perform a histopathological study of the desired characteristics. The upper intertidal is dominated by Echinogammarus marinus, what is explained by their remarkable resistance to desiccation and salinity variation. On the other hand, the species richness is higher in the lower intertidal, even though most of the individuals belong to the species Gammarus locusta. Several parasite taxa were detected by means of light microscopy from individuals of E. marinus and G. locusta including ciliates, gregarines, digeneans, bryozoans, isopods, nematods and other parasitic and commensal worms, the structure of which has been precisely detailed in this document, as well as their effect in the host and prevalence variation throughout the study period. However, most of the effort was concentrated on the identification, ultrastructure description and phylogenetic classification of three main protist parasite taxa; Phyllum Microsporidia, Class haplosporidia (Cercozoa), and Class Mesomycetozoea. Microsporidia are obligate parasites with several species infecting amphipod crustaceans. They often have complicated cycles involving different hosts and developmental stages, including different types of mature spores. Transmitted horizontally or vertically their effects in the host range from muscular loss and other tissue disruption to feminization of the host, as we believe it does the microsporidian parasite infecting G. locusta. In contrast with Microsporidia which comprises around 1500 species, class Haplosporidia barely exceeds the 50 species. Nevertheless, a number of them have strong influence in the health and mortality rates of some organisms, mainly molluscs, with the subsequent impact for humans at economic and even health levels (ex. Haplosporidium nelsoni). According to the molecular analysis of the SSU rDNA of the haplosporidian parasite found in G. locusta, we have presumably identified a novel species. Whether the observed prevalence differences between males and females indicates feminization capacity (already documented in the sister group Paramyxea) still requires further study, as well as the possible positive relation between prevalence and temperature (the trends we observed were not statistically significant). Finally, one last aquatic prostistan parasite found in amphipods from Newton´s Cove presumably belongs to a new clade within the class Mesomycetozoea. In the absence of further ultrastructural and molecular information this novel DRIP is phylogenetically related to the fish parasite Dermocystidium sp.; to 5 Amphibiocystidium sp., responsible of the disappearance of some frog species in Northern Italy; and to Rhinosporidium sp. which parasites some vertebrates including humans. This study, has demonstrated that working with the three main techniques in histopathology (Light microscopy, TEM and molecular) is possible with tissues of the same individual, despite their small size.
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