Metamorphic common toads keep chytrid infection under control, but at a cost

Batrachochytrium dendrobatidis (Bd) causes chytridiomycosis, an infectious disease of amphibians, which has contributed to population declines in hundreds of species worldwide. Common toads (Bufo bufo) exhibit low resistance and relatively high tolerance to Bd infection, which may partly be attributable to bufadienolide toxins secreted in their granular skin glands. Bufadienolides are known to provide an effective defense against several pathogens, parasites, and predators. The toxin production of bufonids is a plastic trait, inducible by several environmental factors. Here, we experimentally infected juvenile common toads with Bd and investigated if the toadlets could clear the infection over time, whether the infection induced bufadienolide production, and whether the infection caused decreased body mass. We found that prevalence remained 100% throughout the entire experimental period, but infection intensity did not increase and it was significantly lower on day 30 than on day 20. At the same time, compared to controls, infected toadlets produced lesser amounts of bufadienolides and their body mass was also lower. These results suggest that although young toadlets may not be able to clear Bd infection on their own, they may be able to keep infection intensities under control. Nonetheless, even if toadlets do not succumb to the disease, the costs of chronic infection may still compromise their fitness.