An Investigation of Chemical Prey Discrimination by Rhabdophis subminiatus Hints the Source of Nuchal Gland Toxins

The nuchal glands are organs of chemical defense embedded under the skin of several species of Rhabdophis and contain toxins sequestered from consumed prey. Rhabdophis subminiatus possesses nuchal glands, but not much information is available on its toxin source and prey preference, particularly based on its chemosensory response. We hypothesized that the response of R. subminiatus toward toads would be higher than other potential prey because the snake needs to sequester toxins contained in toad skin. We also examined the snake preference toward several bufonid species to test a hypothesis that the preference toward Duttaphrynus melanostictus is higher than other toad species due to its high availability in the habitat of the snake. To test the hypotheses, we conducted chemical response tests and compared the tongue-flick attack score (TFAS) of the snake toward prey chemical stimuli. The first experiment used only one toad species (D. melanostictus) and various potential prey animals for the source of chemical stimuli. The second experiment used chemical stimuli from several species of frogs and toads. In the first experiment, snakes showed the highest response toward D. melanostictus. However, in the second experiment, snakes showed the highest response toward a toad, Ingerophrynus biporcatus, followed by D. melanostictus, and a lower response toward another toad, Phrynoidis asper. These results indicate that the snake has a high preference toward toads, but its preference varies among toad species. Taken together, this study suggests that R. subminiatus discriminates different potential prey chemical cues and probably consumes toads to sequester their toxins.