Different chemical cues originating from a shared predator induce common defense responses in two prey species

In freshwater ecosystems, inducible defenses that involve behavioral or morphological changes in response to chemical cue detection are key phenomena in prey-predator interactions. Many species with different phylogenetic and ecological traits (e.g., general activity patterns and microhabitats) use chemical cues to avoid predators. We hypothesized that prey species with a shared predator, but having different ecological traits, would be adapted to detect different chemical cues from the predator. However, the proximate mechanisms by which prey use chemical cues to avoid predation remain little known. Here, we tested our hypothesis by using fractionated chemical components from predatory dragonfly nymphs (Lesser Emperor, Anax parthenope julius) to trigger anti-predator behavioral responses in two anuran tadpoles, the wrinkled frog Glandirana (Rana) rugosa and the Japanese tree frog Hyla japonica. Glandirana rugosa detected chemical cues that had either high or low hydrophobic properties, but H. japonica responded only to chemical cues with hydrophilic properties. During the normal behaviors of these tadpole species, G. rugosa remains immobile in benthic habitats, whereas H. japonica exhibits active swimming at the surface or in the middle of the water column. As we had hypothesized, these tadpole species, which have different general activity levels and microhabitats, detected different chemical cues that were exuded by their shared predator and responded by changing their activities to avoid predation. The specific chemical cues detected by each tadpole species are likely to have characteristics that optimize effective predator detection and encounter avoidance of the shared dragonfly predator.