Hierarchical response to kairomones of predator based on experience acquired through learning

This study investigated how prior experience modulates the anti-predator behavioral responses of Duttaphrynus melanostictus tadpoles to kairomones from the predatory tadpole Hoplobatrachus tigerinus. I compared the responses of four distinct categories of tadpoles; 1) predator-naïve (laboratory-born), 2) indirect predator-experienced (short-term exposure to caged predator cues), 3) direct predator-experienced (short-term direct encounters), and 4) wild-caught (long-term natural experience). A stimulus solution (kairomones) from the predator was used to simulate predation risk. The results showed that tadpoles of D. melanostictus from all experience groups exhibit antipredator behavioral responses, i.e., overall reduced swimming and less time spent swimming, but with a higher burst speed in response to water-borne kairomonal cues of predators. Crucially, the intensity of these antipredator behavioral responses was strongly dependent on experience, following a clear hierarchical gradient: Wild-caught > direct-predator experienced > indirect-predator experienced > predator-naïve > control. The significant, albeit low-level, response of predator-naïve tadpoles indicates that predator recognition is innate. However, the enhanced antipredator behavior of wild-caught tadpoles compared to predator-naïve or direct or indirect predator-experienced tadpoles suggests that learning and cumulative experience are involved. A combination of both innate and learned behaviors could allow tadpoles of D. melanostictus to calibrate their defensive investment necessary for survival.