Biology session

The spread of infectious diseases is one of the main causes of global amphibian declines. The fungus, Batrachochytrium dendrobatidis is the causative agent of chytridiomycosis, which can lead to mass mortality and has been linked to the extinctions of numerous amphibian populations and even some species. The pathogen is known to be present in the Carpathian Basin, however, there is no evidence for dramatic decreases in Hungarian populations. This may be explained by the low virulence of the pathogen’s local strain and/or the high tolerance of local amphibian populations. The common toad (Bufo bufo) is an interesting species in respect to chytridiomycosis, because individuals from Spanish populations were confirmed to be sensitive to infection, according to both field and experimental studies, while its populations in Hungary have not been reported to decrease due to chytridiomycosis. The agile frog (Rana dalmatina) is also interesting, because infection intensities are lower than in related North American species, but this species has not been involved in experimental infection studies yet. In our study, we performed an experimental infection of the two abovementioned amphibian species with a highly virulent, globally distributed Bd strain, originally isolated in Spain. We examined both direct and indirect effects of exposure to Bd during the tadpole stage, and two weeks after metamorphosis. In accordance with our preliminary expectations, agile frogs were less susceptible than common toads at all studied life stages. However, we didn’t observe any mortality, exposure to Bd as well as infection intensity did not affect body mass negatively, and had no significant effect on the length of larval development. According to our results, it appears that Hungarian common toad populations have lower sensitivity to Bd infection than Western European ones, and the agile frog also has a higher tolerance. The underlying mechanism of this phenomenon may be regional differences in chemical defences, which we are planning to investigate in further studies.