Interactions between the information content of different chemical cues affect induced defences in tadpoles

Animals often alter their behaviour, morphology and physiology in the presence of predators. These induced defences can be fine-tuned by a variety of environmental factors such as predator species, acute predation risk or food availability. It has, however, remained unclear what cues influence the extent and quality of induced defences and how the information content of these cues interact to determine the development of antipredator defences. We performed an experiment to study the significance of direct chemical cues, originating from the predators themselves, and indirect cues, released by attacked or consumed prey, for phenotypic responses in Rana dalmatina tadpoles. We reared tadpoles in the presence of caged predators (Triturus vulgaris, Aeshna cyanea) fed either one or three tadpoles every other day outside the tadpole-rearing tanks. Fifteen hours after food provisioning, predators were put back into the tanks containing focal tadpoles either after washing (direct + digestion-released cues) or with the water containing remnants of the prey (direct + all types of indirect cues). Our results suggest that direct cues together with digestion-released cues can be sufficient to induce strong antipredator responses. Induced defences depended on both direct cues, affecting predator-specific responses, and the quantity of indirect cues, resulting in graded responses to differences in predation threat. Moreover, direct and indirect cues interacted in behaviour, resulting in predator-specific graded responses. We also observed a decrease in the extent of predator-induced responses in large tadpoles as compared to small ones. Our results, thus, suggest that prey integrate multiple cues about predators to optimize induced defences and that this process changes during ontogeny.