The Japanese natricine snake Rhabdophis tigrinus sequesters cardiotonic steroids, bufadienolides (BDs), from ingested toads in the nuchal glands as defensive toxins. A previous study showed that R. tigrinus in captivity converts dietary BDs when it sequesters them. However, it is unknown whether the dietary BDs are actually converted and the modified products accumulated under natural conditions. It is also unknown to what extent the BD profile of ingested toads is reflected in that of the snake. We collected 123 snakes from throughout Japan, analyzed their BD profiles by liquid chromatography/mass spectrometry, and identified 15 BDs from R. tigrinus by nuclear magnetic resonance analyses. We also compared their BD profiles using hierarchical cluster analysis (HCA). HCA exhibited two main clusters associated with their collection locations: eastern and western regions of the Japanese main islands. These results, coupled with previous findings on the BDs of Japanese toads, suggest that 1) R. tigrinus converts toad-derived BDs into other compounds under natural conditions; 2) there are both universal and regionally-specific conversions of dietary BDs by R. tigrinus; and 3) geographic variation in toad BD profiles is partially reflected in the variation of snake BD profiles.

日本毒蛇Rhabdophis tigrinus从摄入蟾蜍的颈部腺体中分离强心类固醇，蟾蜍二烯内酯 (BD) 作为防御性毒素。之前的一项研究表明，圈养的虎鲸在隔离饮食中的 BD 时会转化它们。然而，饮食中的BDs是否真的被转化，并且修饰的产物是否在自然条件下积累尚不清楚。也不清楚摄入的蟾蜍的 BD 特征在多大程度上反映在蛇的 BD 特征中。我们收集了来自日本各地的 123 条蛇，通过液相色谱/质谱法分析了它们的 BD 谱，并从R. tigrinus 中鉴定了 15 条 BD通过核磁共振分析。我们还使用层次聚类分析 (HCA) 比较了他们的 BD 配置文件。HCA 展示了两个与其收集地点相关的主要集群：日本主要岛屿的东部和西部地区。这些结果，加上之前对日本蟾蜍 BDs 的发现，表明 1) R. tigrinus在自然条件下将蟾蜍衍生的 BDs 转化为其他化合物；2) R. tigrinus对饮食 BD 进行了普遍和区域特定的转换；3）蟾蜍BD剖面的地理变异部分反映在蛇BD剖面的变异上。