Evolution of the nuchal glands in snakes: Synthesis from morphology, ethology and physiology

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Nucho-dorsal glands are unique organs that have been reported in only 15 species of snakes. Rhabdophis tigrinus, one of the species that have the glands, eats toads, which have toxic skin secretions, and sequesteres the toxins to store in its glands. This species also shows peculiar defensive displays that enhance the effectiveness of the toxins for predator avoidance.I clarified phylogenetic relationships among species that have the nucho-dorsal glands and related species, and inferred the evolutionary process of the defensive system depending on the glands, which involves a suite of correlated features of morphology, physiology, behavior, and ecology. In addition, the obtained phylogenetic tree suggested that the evolutionary loss of the glands have independently occurred twice, for which I proposed a hypothesis of the evolutionary factors that have caused the loss of the glands.