Temperature effects on production of infectious zoospores from chytrid-infected Xenopus laevis

A leading cause of global declines in amphibian populations is chytridiomycosis, the temperature-dependent pandemic disease, caused by the fungal pathogen Batrachochydrium dendrobadtidis (Bd). Temperature fluctuations caused by climate change could exacerbate this disease. Temperature-dependent models of Bd infections can provide important insights into Bd transmission dynamics in frog populations to help inform management actions. The Raffel lab has been working on a novel type of mechanistic model to predict Bd and host responses to fluctuating temperatures, based on a combination of metabolic theory and a type of dynamic model traditionally used to describe macroparasite dynamics. In this model shedding rate (i.e., the number of zoospore equivalents released per minute) of Bd zoospores from an infected host’s skin constitutes an important parameter which we were able to measure. We infected 124 juvenile Xenopus laevis and subjected them to acclimation temperatures of 10 °C, 15 °C, or 20 °C for 35 days. All frogs were inoculated the day of performance temperature switch which happened at the end of the acclimation period; however, 38 were also inoculated 35 days before the switch. During the performance period frogs were subjected to temperatures of 10 °C, 15 °C, 20 °C, or 25 °C for 35 days. Shed zoospores were collected 7 days and 35 days post performance temperature switch. On day 7 of the performance period, shedding rate differed between each performance temperature, but not with acclimation temperature (Table 3). A higher shedding rate was also observed with lower performance temperatures. Shedding rate on day 35 of the performance period did not differ between each performance temperature and acclimation temperature. Shedding rate was also significantly lower on day 35 (Table 3). Frogs inoculated 35 days before the performance temperature switch did not differ between frogs inoculated the day of the switch. We also found Infection intensity and levels of shed zoospores were correlated (Table 3), with filters having detected more zoospores day 7 of the performance period compared to swabs collected at the same time point. We conclude shedding rate from X. laevis is affected by temperature, and infection load. This research will help to inform the transmission parameter for the mathematical model our lab has been generating to untangle the complex temperature dependence of Bd disease dynamics in frog populations which will potentially help conservation programs.