The poisonous snake, Rhabdophis tigrinus, protects itself from predators with a deadly poison in the subcutaneous organ "cervical gland" on the back of the neck.The main component of the venom is the cardiotonic steroid bufadienolide, which is derived from the toad that feeds on it.There are 17 species of Rhabdophis tigrinus in the world that have such cervical glands.One of them is the worm, Rhabdophis tigrinus, which preys on earthworms in southwestern China, and is said to have changed its staple food from frogs to earthworms in the process of evolution.

　However, bufadienolide was not detected in the staple food earthworms.This time, analysis of the toxic component of the cervical gland of Rhabdophis tigrinus revealed that it was a type of bufadienolide, and further analysis of its molecular structure revealed that it was derived from the firefly of the subfamily Pyrocoelia, which inhabits North America, not the frog. It matched.

　Therefore, we analyzed five species of fireflies of the subfamily Pyrocoelia that inhabit Asia (China, Taiwan, Japan).As a result, bufadienolide was detected in all the extracts, and the structure was similar to that of bufadienolide derived from Rhabdophis tigrinus.Furthermore, it was confirmed that the Itsurokoyamakagashi actually prey on fireflies.

　This indicates that in the process of evolution to Rhabdophis tigrinus within the genus Rhabdophis tigrinus, the eating habits changed from a frog diet to an earthworm diet, and along with this, fireflies were used as the source of bufadienolide instead of toads.There is no other example of the transfer of toxic sources to such systematically and ecologically distant foods, and this is a result that provides a new perspective for research on the ecology of snakes and changes in the eating habits of animals.

Paper information:[PNAS] Dramatic Dietary Shift Maintains Sequestered Toxins in Chemically Defended Snakes