Aspects Of The Transmission Ecology And Life History Of Hematodinium Perezi In Juvenile Blue Crabs, Callinectes Sapidus

Parasitism is one of the most common lifestyles found in eukaryotes. Parasites account for substantial biomass and are major links in the food web. In the past two decades, our understanding of the ecological role of parasites has significantly advanced through theoretical and empirical studies. These research studies, however, rarely overlap with those involving protistan parasites, where efforts have focused on either disease prevention and management in humans and economically important species, or on their phylogenetics, revealing evolution of parasitism and specialization. Despite their vast diversity, protistan parasites are much less studied in comparison to other eukaryotic kingdoms due to their microscopic nature and high phenotypic diversity. The order Syndiniales is a group of dinoflagellates comprised exclusively of parasites with a pan-global distribution. However, only two genera, Hematodinium and Amoebophrya, have been well documented in terms of their pathology and ecological impact on hosts. This dissertation focuses on the parasite Hematodinium perezi in juvenile blue crabs. Hematodinium perezi is a parasitoid that kills its host as a prelude to transmission. Several knowledge gaps in the transmission and life history of this parasite are addressed in these studies. Chapter 1 documents the establishment of natural transmission in the laboratory and examines transmission dynamics of H. perezi in juvenile blue crabs and its relation to dinospore densities released under controlled environments. Heavy infections were found in infected naïve crabs after 30 days, suggesting rapid progression of the infection under high temperatures. Chapter 2 examines the transmission of H. perezi at a community level, using both laboratory and field experiments, with the hypothesis that oysters, as efficient filter feeders, may act to dampen, or dilute transmission of H. perezi by feeding on dinospores that might otherwise infect crabs. Field deployments suggest oysters reduce the probability of H. perezi infection in naïve crabs, supporting the dilution effect, whereas in the laboratory experiments, dinospore densities in the water were reduced by oysters over a short time frame of one hour. Finally, Chapter 3 focuses on the two different dinospore stages, micro- and macro-dinospores, of H. perezi and investigates their functions in relation to the previously unknown sexual cycle of H. perezi, using laboratory experiments, flow cytometry, and comparative transcriptomics to uncover several aspects of these rather cryptic stages. The micro-dinospore stage was shown to be directly transmitted to naïve crabs. The macro-dinospore stage was not infectious in our studies, and its function remains to be determined. The two dinospore stages have twice the DNA content of ameboid trophont, indicating sexual fusion of H. perezi likely occur inside the crab host, and the two dinospore stages represent alternative life history strategies with different transcriptomic profiles.