One of the major factors driving the currently ongoing biodiversity crisis is the
anthropogenic spread of infectious diseases. Diseases can have conspicuous consequences,
such as mass mortality events, but may also exert covert but similarly severe effects,
such as sex ratio distortion via sex‐biased mortality. Chytridiomycosis, caused by
the fungal pathogen Batrachochytrium dendrobatidis (Bd) is among the most important
threats to amphibian biodiversity. Yet, whether Bd infection can skew sex ratios in
amphibians is currently unknown, although such a hidden effect may cause the already
dwindling amphibian populations to collapse. To investigate this possibility, we collected
common toad ( Bufo bufo ) tadpoles from a natural habitat in Hungary and continuously
treated them until metamorphosis with sterile Bd culture medium (control), or a liquid
culture of a Hungarian or a Spanish Bd isolate. Bd prevalence was high in animals
that died during the experiment but was almost zero in individuals that survived until
the end of the experiment. Both Bd treatments significantly reduced survival after
metamorphosis, but we did not observe sex‐dependent mortality in either treatment.
However, a small number of genotypically female individuals developed male phenotype
(testes) in the Spanish Bd isolate treatment. Therefore, future research is needed
to ascertain if larval Bd infection can affect sex ratio in common toads through female‐to‐male
sex reversal.
