Causes of Infection and Disease Progression of Hematodinium sp. in the Tanner crab, Chionoecetes bairdi

Abstract

In the past several decades, parasites of the genus Hematodinium have become prevalent in crustaceans around the globe. One such host is the Tanner crab (Chionoecetes bairdi), which supports a number of commercially and culturally valuable fisheries in the North Pacific. This thesis explores the host-parasite relationship between C. bairdi and Hematodinium sp. through two avenues. The first was an analysis of gene expression, in which individual crabs were captured, their infection status was checked, and they were exposed to one of three temperatures - elevated, decreased, and control. Throughout the 17-day experiment, hemolymph was drawn and sequenced for gene expression. Differences in gene expression for both host and parasite were then analyzed, and a number of genes in both host and parasite were identified as linked to temperature response. Numerous parasite expression pathways changed over the course of the experiment, including changes in RNA processing and microtubule development. The second avenue of analysis utilized generalized linear mixed models to investigate a long-term survey dataset from southeast Alaskan crab surveys, with the goal of determining the association between infection status and a variety of biological and environmental factors. A number of factors were found to be correlated to infection status. Among them: females were more likely to be infected than males, immature crab were more likely to be infected than mature individuals, recently-molted crabs were more likely to be infected, and larger crabs were more likely to be infected. Together, these findings improve our understanding of the relationship between C. bairdi and Hematodinium. They provide a window into the internal host-parasite dynamics and how temperature and time alter gene expression. They also demonstrate that infection rates vary substantially within subsets of the host population, and indicate those subset-specific impacts should be considered when analyzing the ramifications of outbreaks.