Can Exotic Toad Toxins Kill Native Ryukyu Snakes? Experimental and Field Observations on the Effects of Dinodon rufozonatum walli

Abstract

Bufo marinus is a large toxic toad that was recently introduced to Ishigakijima of the Yaeyama Islands, Southern Ryukyus, Japan. In a previous study, the native Southern Ryukyu snake, Dinodon rufozonatum walli, did not die after ingestion of a single juvenile toad. Considering the current high density of the toads on Ishigakijima, however, it is highly likely that an individual snake may have an opportunity in the field to swallow more than one toad in succession. Therefore, we experimentally investigated the occurrence of voluntary multiple ingestions of juvenile toads by this snake and their effects on the snake. In addition, we obtained from the inhabitants of Ishigakijima some field records of dead snakes that had apparently been killed by the cane toads (sometimes larger than the juveniles used in our experiment). The experiment showed that the snake may often voluntarily seize two or more juvenile toads at once, and may die while swallowing them. These results and the field records suggest that the D. r. walli population on Ishigakijima has been seriously affected by the feral toad population by ingesting this toxic prey.