Tadpoles exposed to predation risk display a wide range of antipredator phenotypic plasticity. The induction of these responses, as well as their evolutionary and ecological significance, has been studied extensively. However, the underlying proximate mechanisms are largely unknown. We have previously found that a stress hormone (corticosterone, CORT) mediates both behavioral and morphological responses to predation risk in ranid tadpoles. In this study, we focused on identifying how the development of the induced tail morphology in wood frog (Lithobates [=Rana] sylvaticus) tadpoles influences their escape performance when attacked by predatory larval dragonflies (Anax junius). Using a series of daily predation trials, we recorded the time to capture and number of successful escapes of tadpoles raised with and without dragonflies and with and without exogenous CORT or metyrapone (a corticosteroid synthesis inhibitor).
Results/Conclusions
We detected no differences initially among tadpoles from each treatment in tail morphology, mean time to capture, or number of successful escapes. After eight days, tadpoles exposed to larval dragonflies and/or exogeneous CORT had developed deeper tail muscles. These tadpoles also experienced significantly longer times to capture than tadpoles from the other treatments. The increased times to capture were driven by an increase in the number of successful escapes. The results further link the predator-induced physiological stress response in wood frog tadpoles to the expression of an antipredator morphology and to an adaptive benefit in survival probability mediated by improved escape performance. Identifying the physiological mechanisms regulating antipredator phenotypic plasticity will improve our ability to understand how multiple traits are integrated and what the consequences are to prey and their interactions with predators.