HUTCHINSON, Deborah A.*; SCHROEDER, Frank C.; SAVITZKY, Alan H.; MORI, Akira; MEINWALD, Jerrold; BURGHARDT, Gordon M.; Old Dominion Univ.; Cornell Univ.; Old Dominion Univ.; Kyoto Univ.; Cornell Univ.; Univ. of Tennessee: Dietary Toxin Sequestration in Two Populations of a Toad-Eating Snake, Rhabdophis tigrinus

Rhabdophis tigrinus (Colubridae: Natricinae) is a bufophagous (toad-eating) snake from Asia that possesses unusual defensive glands under the skin on the dorsal surface of the neck. These nuchal glands have been reported to contain bufadienolide steroids similar to those that toads produce from cholesterol precursors. However, morphological and behavioral evidence has suggested that Rhabdophis does not synthesize defensive bufadienolides but rather sequesters them from ingested toads. In support of this hypothesis, we recently demonstrated that Rhabdophis must be born to a chemically-defended dam or consume a diet of toads in order to express bufadienolides in the nuchal glands. In this study we compared the composition of nuchal gland fluid in animals from toad-rich and toad-free islands. Nuchal gland fluid was collected from hatchlings from these two localities after they had been fed diets either containing or lacking toads. These samples plus extracts of the bufonid prey were analyzed with ¹H-NMR and HPLC. Rhabdophis from the toad-free island lacked bufadienolides in their nuchal glands and accumulated the toxins only when fed toads. In contrast, all hatchlings from the toad-rich island contained bufadienolides in their nuchal glands regardless of diet. These data provide further evidence of dietary toxin sequestration and maternal provisioning of bufadienolides by Rhabdophis.