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Drivers of winter infection dynamics of an amphibian pathogen
Infectious diseases are becoming increasingly common and problematic for wildlife populations in many parts of the world. Disease prevalence and severity fluctuate over time, often due to the ubiquitous pressure of seasonality, or the cyclic changes in ecological systems. However, for many host-pathogen systems, our understanding of important seasonal drivers of disease remains fragmented. For example, when seasonality of a disease is studied in medium and high latitudes, winter is often neglected, despite this being a period of physiological and immunological challenges associated with extreme environmental conditions. Therefore, my aim is to examine drivers of winter Infection dynamics of the amphibian fungal pathogen Batrachochytrium dendrobatidis. First, B. dendrobatidis infection prevalence was measured from spring through fall to understand local infection levels and anthropogenic influences (Chapter 1). Next, laboratory experiments examined the effects of B. dendrobatidis on critical thermal minimum of two anuran species to identify how this pathogen influences the ability of hosts to survive winter (Chapter 2). Another laboratory experiment tested how road de-icing salt (commonly used in winter) influences B. dendrobatids and a tadpole host condition and subsequent host-pathogen interactions (Chapter 3). Finally, a field-based exploration of B. dendrobatidis infection dynamics was conducted during winter to understand how infections vary during in this season and between two overwintering strategies (Chapter 4). Winter infection dynamics in many host-pathogen systems are largely understudied, but the knowledge gained by this work can demonstrate how harsh environmental conditions of winter that can exacerbate otherwise benign infections, and affect the ability of hosts to sustain infections during winter. This work can therefore inform predictions and investigations of infection dynamics in subsequent seasons to better understand the seasonality of wildlife diseases.