Antipredator responses of Indosylvirana indica tadpoles do not match the level of predation risk

Abstract

Predators are the key regulators of prey populations in different environments. However, they are not always present but often come and go. Moreover, the level of predation risk varies based on habitat complexity, resource availability and other ecological factors. Hence, it is adaptive for prey animals to match their antipredator responses with the level of predation risk as such responses are costly to produce and maintain, and there exists a trade-off between fitness-enhancing and fitness-reducing activities. To test whether larval Indosylvirana adjust their antipredator responses based on the level of predation risk, we designed an experiment in which tadpoles of Indosylvirana indica were exposed to nil, low, moderate or high levels of predation risk to assess the effect of risk on growth, behaviour, morphology and life-history traits. We also determined the whole-body corticosterone levels to assess the physiological changes associated with the level of predation risk. Our results show that the growth rate of tadpoles experiencing varying levels of predation risk was similar although there was a trend towards a higher growth rate at moderate and high risks. Surprisingly, tadpoles experiencing predation risk did not reduce their activity. However, the activity of tadpoles experiencing differential predation risk was comparable. Similarly, the use of shelter was comparable among tadpole groups, with an overall higher level of activity in the afternoon compared to other times. Although a few morphological traits were different among tadpole groups, there was no trend or pattern. Moreover, these morphological alterations did not contribute to overall tadpole shape changes. Physiologically, tadpoles experiencing predation risk had significantly lower levels of corticosterone compared to those without risk. Interestingly, corticosterone titres among tadpoles facing varying levels of predation risk were similar. Metamorphic traits of individuals in the various predation risk groups were significantly different. Tadpoles experiencing moderate and high risks emerged at a larger size, and those experiencing the highest level of risk metamorphosed at the earliest. The results of our study thus show that the antipredator responses of larval I. indica do not match the level of predation risk, indicating that physiological and ecological constraints could limit the extent to which prey species respond to predation risk and its intensity.