Abstract

The ciliated protozoa represent one of the most diverse and widespread groups of commensal and parasitic organisms in marine and freshwater environments; however, our understanding of certain taxa and their associations with crustacean hosts is still limited. Four species from two ciliate subclasses were observed attached to the exoskeleton of the marine amphipod Echinogammarus marinus. The chonotrich ciliate Heliochona sp. was attached predominantly to the pleopods. In contrast, two stalked peritrichs appeared to be generalist epibionts and were ubiquitously distributed on the host animals. The loricated peritrich Lagenophrys tattersalli was attached exclusively to the coxal gills, this ciliate was highly prevalent and presented with a moderate to high intensity of infection among the amphipods sampled; the remainder of the present study was devoted to the taxonomy, molecular phylogenetics and ecology of this obligate ectocommensal. Lagenophrys is a genus of suspension feeding ciliates currently comprising 63 valid species, all of which form obligate ectocommensal associations with marine and freshwater crustaceans. Identification is based principally on the structure and morphology of the lorica and lorica aperture; however, the molecular taxonomy of this genus is under-represented in comparison to other peritrich taxa. A comprehensive morphometric analysis of the lorica and lorica aperture of L. tattersalli was undertaken, similarities in the structure, morphology and asymmetry of the anterior and posterior lips of the lorica aperture were compared to two morphologically similar species. Furthermore, the present study isolated a partial sequence of the 18S SSU-rRNA gene for the first time. The sequence recovered consisted of 685 basepairs. Phylogenetic analyses based on sequences available in the GenBank database indicates that L. tattersalli is most closely related to other loricated peritrich in the genus Usconophrys and the genus Vaginicola. The Lagenophryidae have also evolved life-histories that enable them to effectively exploit crustacean physiology; in many species this restricts their distribution to a specific micro-habitat on the host. Lagenophrys tattersalli was found attached exclusively to the coxal gills of E. marinus with the intensity of infection being highest on paired coxal gills present at the three posterior-most pereon positions; there was no significant difference in the intensity of infection and the sexual phenotype of the host animal. Using the morphometric data gathered from the lorica, it was determined that a significant proportion of the amphipods gill surface area (<17.0%) was occupied by the ciliate infrapopulation, however there were no apparent indications of inflammation or secondary infection associated with incidences of high intensities of infection. Moulting directly affects epibiotic and obligate ectocommensal ciliates; there is a significant risk of being shed from the host with the exuvium unless the ciliates can transfer successfully to the new exoskeleton. Examination of the coxal gills of female amphipod in the early post-moult stage suggests only a small proportion of the pre-moult infrapopulation of L. tattersalli was able to transfer successfully from the exuvia during ecdysis.

Additional Notes

Supervisors: Dr. Alex Ford and Dr. Simon Cragg

Course: Master of Philosophy - MPhil

Date Deposited: 2017-05-08

URI/permalink: https://library.port.ac.uk/dissert/dis12866.html