Chytridiomycosis, a disease of amphibians caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is an ideal system for studying how temperature influences the host-pathogen relationship because both the host and the pathogen are ectothermic. In this dissertation, I employ a three-pronged approach to investigate the relationship between temperature and the prevalence, severity, and outcome of Bd infections in Northern cricket frogs (Acris crepitans) using both laboratory experiments and field studies. In Chapter One, I conducted a Bd exposure study to determine whether constant temperatures affect Bd pathogenesis differently in live hosts than in culture. Exposure frogs were inoculated weekly with 100 million zoospores of a virulent strain of Bd and frogs were incubated at one of six temperatures: 11, 14, 17, 20, 23, or 26°C. Infection prevalence and pathogen load in Bd-exposed frogs were highest at 14°C while survival was lowest at 11˚C. These results demonstrate that Bd pathogenicity peaks at different temperatures in live hosts than Bd growth peaks at in culture. In Chapter Two, I combine a field study that assesses the effect of microhabitat choice, seasonality and latitude on Bd prevalence and severity in wild amphibian populations with a laboratory study that investigates how temperatures that fluctuate during diurnal and nocturnal cycles influence Bd pathogenicity. Across all states, I found that year was the only significant predictor of infection prevalence, but probability of infection was predicted by year, month, and latitude, and pathogen load was predicted by month and body temperature. In my experimental study, I found infection prevalence and pathogen load to be highest, and survival lowest, in the Louisiana winter group (7˚-17˚C). In my third chapter, I used a biophysical model, Niche Mapper, to predict probability of survival and infection prevalence in Northern cricket frogs by modelling host body temperature. I found that the probability of an infected frog surviving thirty days in May was highest in Southern Louisiana and lowest in Northern Michigan. These studies demonstrate that temperature is an important influence on infection outcome in live hosts. / 1 / Julia Madeleine Sonn