Do antipredator responses of Euphlyctis cyanophlyctis tadpoles depend on the intensity of predation risk?

Abstract

Successful coexistence with predators depends on the ability of prey to strike a balance between the costs of predator avoidance and the benefits of foraging and reproducing as there is a trade-off between these activities. Prey animals can balance this trade-off by responding to predation risk in a manner that matches the intensity of risk posed by the predator, which is known as the threat-sensitive predator avoidance hypothesis. To test this hypothesis, we exposed larval Indian skipper frogs (Euphlyctis cyanophlyctis) to different intensities of predation risk by increasing the number of predators and the amount of biomass consumed and recorded their behaviour, morphology, and metamorphic traits. We also quantified the whole-body corticosterone to assess the physiological basis of alterations in morphology, behaviour, and life-history traits. The results indicate that behavioural responses of larval skipper frogs increased with the intensity of risk conforming to the predictions of the threat-sensitivity hypothesis. However, the morphological responses did not vary with the intensity of risk and hence did not support the predictions of the hypothesis. Interestingly, tadpoles facing a higher level of predation risk metamorphosed at the largest size, but with increased larval duration. At the physiological level, corticosterone levels increased with increases in the intensity of risk. Thus, our results suggest that certain antipredator responses may vary with the intensity of risk while others may not. Further, the results of our study also show an association between physiological and behavioural responses of larval E. cyanophlyctis to predation risk. More importantly, we show that larval skipper frogs can assess the intensity of predation risk through threat-sensitive learning by associating conspecific alarm cues with odours of dragonfly nymphs.