Levels of Predation Modulate Antipredator Defense Behavior and Metamorphic Traits in the Toad Bufo melanostictus

The influence of the presence of nonlethal predators on antipredator defense behavior and metamorphic traits was studied in the toad Bufo melanostictus. Tadpoles reared with caged predaceous tadpoles of Hoplobatrachus tigerinus delayed metamorphosis and also emerged at a smaller size compared to those in a predator-free environment. Different predaceous cues (kairomones, alarm cues and dietary cues, derived after feeding the predator with conspecific prey) induced increase in stationary phase and swimming speed and decrease in swimming spurts and time used for feeding. The intensity of defense behaviors varied with the cue. They were more intense in response to cues of predators fed on conspecific prey item. The response to alarm cues or kairomones or predators fed on heterogeneric tadpole species was similar but lower in magnitude compared to that elicited in response to predators fed on conspecific prey item. Most intense defense behavior in response to the odors of the predator that consumed conspecific members is possibly caused by a combined effect of kairomones, alarm, and dietary cues. The findings suggest that B. melanostictus tadpoles are capable of assessing levels of predation risk and modulating the intensity of their defense behavior in accordance with the perceived threat. Interestingly, despite longer larval period, size at metamorphosis of the toadlets was smaller in the presence of caged predator.