Gregarine apicomplexans are a diverse but poorly understood group of single-celled parasites infecting a wide range of invertebrates in marine, freshwater and terrestrial environments. My thesis focuses on marine gregarines. Gregarines from marine hosts are unique because some (archigregarines) have maintained a set of pleisiomorphic characteristics from the ancestor of gregarines and apicomplexans alike. Other lineages of marine gregarines (eugregarines) are thought to have been modified from this archigregarine morphotype, and represent a wide-range of diversity with regard to general morphology, motility, and feeding strategies. My work has broadly applied molecular phylogenetics to novel species of marine gregarines from areas around British Columbia, Canada and Okinawa, Japan, with the goal of placing the evolution of gregarines in a molecular phylogenetic context. I amplified mainly SSU rDNA from a distinct life history stage (trophozoites), and coupled that with morphological data I gathered from light, confocal, as well as electron microscopy. Although my work was unable to resolve deep phylogenetic relationships among gregarines (and apicomplexans), this work did improve our understanding of evolution within gregarines. With the discovery of Veloxidium leptosynaptae from the gut of an echinoderm in Bamfield, British Columbia, and Surculinium glossobalanae from a hemichordate in Okinawa, I was able to show the paraphyly of the archigregarine morphotype, and polyphyly of other gregarine lineages, including some groups of neogregarines and eugregarines in terrestrial and freshwater environments. With the description Polyplicarium, my work uncovered and identified an ambiguous environmental sequence clade and, along with other work on Selenidium, was able to show that SSU rDNA can be reliably isolated from single cells as a method for delimiting closely related or morphologically similar species. In my final data chapter, I conducted an in-depth study on the morphology and molecular phylogenetic relationships between two sister species from the same host, Selenidium terebellae, and a newly discovered species, Selenidium melitzanae. Results from this data gave me the first opportunity to compare character evolution and niche partitioning among closely related gregarines, and provided another example of convergence of the eugregarine morphotype.Science, Faculty ofZoology, Department ofGraduat
