Several Asian natricine snakes are known to possess special organs called nuchal glands. Extensive studies on the nuchal glands of Rhabdophis tigrinus have shown that the glands contain cardiac steroidal toxins known as bufadienolides, which are sequestered from its toad prey and are stored in the nuchal glands as defensive substances. In addition, several species of snakes with nuchal glands exhibit unique behaviors to enhance the effects of the glands (nuchal gland-related behaviors). Macropisthodon rudis is the only species that does not have the nuchal glands in the genus. We investigated its antipredator displays and chemical preference for toads to gain insight into the evolution of the nuchal glands. The results showed that M. rudis does not exhibit the nuchal gland-related behaviors such as neck arching, neck butting, and dorsal-facing posture. Additionally, this species showed high preference for toad chemicals. These results support a previous hypothesis that preference for toads predates the evolution of the nuchal glands and that the unique antipredator behaviors have evolved to enhance the defensive efficiency of the glands.
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Vol. 31 • No. 1