Biology session

Chytridiomycosis, an emerging infectious disease poses a serious threat to amphibian biodiversity. This disease has already led to the drastic decline or extinction of many species. It is caused by the chytrid fungus, Batrachochytrium dendrobatidis (Bd), which was described in 1998. However, despite the global research efforts of the last two decades, our knowledge on Bd ecology is still fragmented. Accurate information on the thermal ecology of the fungus could form the basis of an effective, chemical-free method of disinfection. Based on previous studies it seems that the critical thermal maximum of Bd is lower than that of most amphibian hosts, which provides the possibility to use heat-treatment against chytridiomycosis.

The aim of our study was to determine the combinations of temperature and exposure duration necessary to clear Bd from common toad (Bufo bufo) tadpoles. We infected tadpoles experimentally with a widespread and hyper-virulent strain of Bd. Then we exposed individuals to five different temperatures (22, 27, 28, 29 and 30 °C) for one of three exposure durations (2 days, 4 days, 6 days). We also tested whether the treatment had an effect on the length of larval development and body mass of tadpoles.

Our results showed that exposure to 30 °C or lower temperatures for 2 days were not sufficient for clearing Bd. Heat-treatments lasting for 4 days reduced the amount of Bd, but only 30 °C eliminated it completely. Treatment for 6 days with 28 °C or above completely cleared Bd. Length of the larval development did not depend on infection and was shorter at 27 and 28 °C than at 22, 29 and 30 °C. This difference grew together with the exposure time. Body mass was lowered by experimental infection, and individuals exposed to higher temperatures exhibited lower mass at the end of metamorphosis.

Overall, our research provided important insights into the thermal ecology of Bd. Keeping individuals for 6 days at temperatures of 28 °C or higher can be an effective method of disinfection in case of tadpoles. Nonetheless, it will be important to gather more detailed information about how the pathogenicity of the fungus depends on environmental temperature.