A study explores how some species of venomous snakes sequester prey-derived toxins following an evolutionary shift in diet. The Japanese colubrid snake Rhabdophis tigrinus, which typically feeds on frogs and poisonous toads, accumulates potent toxins called bufadienolides in its neck glands. The toxins are derived from the toads and can perturb heart function in the snake's predators. One group of Rhabdophis snakes, called the R. nuchalis Group, however, has evolved to feed primarily on nontoxic earthworms, rather than frogs and toads; the snakes nonetheless harbor bufadienolide toxins. To uncover the source of the snakes' toxins, Akira Mori and colleagues performed a series of laboratory feeding preference tests and analyzed bufadienolides in gland fluids from R. nuchalis group members. Analysis revealed that the snakes' bufadienolides closely resembled those produced by fireflies of the family Lampyridae. Feeding tests confirmed the snakes' predilection not only for earthworms but also for the fireflies, whose larvae were also detected in the snakes' guts. The findings suggest that an evolutionary shift in the snakes' primary diet--from frogs to earthworms--was accompanied by an expansion of dietary range and a compensatory shift in the source of the snakes' sequestered toxins. According to the authors, the study demonstrates the species' ability to retain a prey-derived defense mechanism despite a drastic shift in diet from vertebrate to invertebrate prey.
Article # 19-19065: "Dramatic dietary shift maintains sequestered toxins in chemically defended snakes," by Tatsuya Yoshida, Rinako Ujiie, et al.
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Proceedings of the National Academy of Sciences