Do predators prefer toxic animals? A case of chemical discrimination by an Asian snake that sequesters firefly toxins.

Several Asian natricine snakes of the genus feed on toads and sequester steroidal cardiac toxins known as bufadienolides (BDs) from them. A recent study revealed that species of the Group ingest lampyrine fireflies to sequester BDs. Although several species of fireflies are distributed in the habitat of the Group, only lampyrine fireflies, which have BDs, are included in the diet of these snakes. Thus, we hypothesized that the Group chemically distinguishes fireflies that have BDs from those that do not have BDs. We also predicted that the Group detects BDs as the chemical cue of toxin source. To test these predictions, we conducted 3 behavioral experiments using , which belongs to the Group. In the first experiment, showed a moderate tongue flicking response to cinobufagin, a compound of BDs. On the other hand, the snake showed a higher response to the chemical stimuli of lampyrine fireflies (BD fireflies) than those of lucioline fireflies (non-BD fireflies). In the second experiment, in which we provided live BD and non-BD fireflies, the snake voluntarily consumed only the former. In the third, a Y-maze experiment, the snake tended to select the chemical trail of BD fireflies more frequently than that of non-BD fireflies. These results demonstrated that discriminates BD fireflies from non-BD fireflies, but the prediction that BDs are involved in this discrimination was not fully supported. To identify the proximate mechanisms of the recognition of novel toxic prey in the Group, further investigation is necessary.