Exposure to Batrachochytrium dendrobatidis affects chemical defences in two anuran amphibians, Rana dalmatina and Bufo bufo

1. Batrachochytrium dendrobatidis (<i>Bd</i>) is the causative agent of chytridiomycosis, one of the major causes of worldwide amphibian biodiversity loss. Many amphibians exhibit skin-based chemical defences which may play an important role against invading pathogens, but whether the synthesis of these chemical compounds is enhanced or suppressed in the presence of pathogens is largely unknown. 2. Here we investigated direct and indirect effects of larval exposure to the globally distributed and highly virulent <i>Bd-GPL</i> strain on skin secreted chemical defences and life history traits during early ontogeny of agile frogs (<i>Rana dalmatina</i>) and common toads (<i>Bufo bufo</i>). 3. Exposure to <i>Bd</i> during the larval stage did not result in enhanced synthesis of the antimicrobial peptide Brevinin-1Da in <i>R. dalmatina</i> tadpoles or in increased production of bufadienolides in <i>B. bufo</i> tadpoles. However, exposure to <i>Bd</i> during the larval stage had a carry-over effect reaching beyond metamorphosis: both <i>R. dalmatina</i> and <i>B. bufo</i> froglets contained smaller quantities of defensive chemicals than their <i>Bd</i>-naïve conspecifics in the control treatment. 4. Prevalence of <i>Bd</i> and infection intensities were very low in both larvae and metamorphs of<i> R. dalmatina</i>, while in <i>B. bufo</i> we observed high <i>Bd</i> prevalence and infection intensities, especially in metamorphs. At the same time, we did not find a significant effect of <i>Bd</i>-exposure on survival, body mass or development rate in larvae or metamorphs in either species. 5. The lack of detrimental effect of <i>Bd</i>-exposure on life history traits, even parallel with high infection intensities in case of <i>B. bufo</i> individuals, is surprising and suggests high tolerance of local populations of this two species against <i>Bd</i>. However, the lowered quantity of defensive chemicals may compromise antimicrobial and antipredatory defences of froglets, which may ultimately contribute to population declines also in the absence of conspicuous mass-mortality events.