Predator-induced changes in the chemical defence of a vertebrate.

1. Inducible defences are ubiquitous in the animal kingdom, but little is known about facultative changes in chemical defences in response to predators, especially so in vertebrates. 2. We tested for predator-induced changes in toxin production of larval common toads (Bufo bufo), which are known to synthesize bufadienolide compounds. 3. The experiment included larvae originating from three permanent and three temporary ponds reared in the presence or absence of chemical cues of three predators: dragonfly larvae, newts or fish. 4. Tadpoles raised with chemical cues of predation risk produced higher numbers of bufadienolide compounds and larger total bufadienolide quantities than predator-naive conspecifics. Further, the increase in intensity of chemical defence was greatest in response to fish, weakest to newts and intermediate to dragonfly larvae. Tadpoles originating from temporary and permanent ponds did not differ in their baseline toxin content or in the magnitude of their induced chemical responses. 5. These results provide the first compelling evidence for predator-induced changes in chemical defence of a vertebrate that may have evolved to enhance survival under predation risk.