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

核背腺是一种独特的器官，只在15种蛇中被报道过。虎纹夜蛾是一种有腺体的物种，它吃具有有毒皮肤分泌物的蟾蜍，并将毒素隔离起来储存在它的腺体中。该物种还表现出独特的防御表现，增强了毒素对捕食者躲避的有效性。我澄清了具有核背腺的物种与近缘物种之间的系统发育关系，并推断了依赖核背腺的防御系统的进化过程，涉及一系列相互关联的形态、生理、行为和生态特征。此外，获得的系统发育树表明，腺体的进化丢失已经独立发生了两次，为此，我提出了导致腺体丧失的进化因素的假说。

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.