Hutchinson Deborah A, Mori Akira, Savitzky Alan H, Burghardt Gordon M, Wu Xiaogang, Meinwald Jerrold, Schroeder Frank C
Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529, USA.
Proc Natl Acad Sci U S A. 2007 Feb 13;104(7):2265-70. doi: 10.1073/pnas.0610785104. Epub 2007 Feb 6.
The Asian snake Rhabdophis tigrinus possesses specialized defensive glands on its neck that contain steroidal toxins known as bufadienolides. We hypothesized that R. tigrinus does not synthesize these defensive steroids but instead sequesters the toxins from toads it consumes as prey. To test this hypothesis, we conducted chemical analyses on the glandular fluid from snakes collected in toad-free and toad-present localities. We also performed feeding experiments in which hatchling R. tigrinus were reared on controlled diets that either included or lacked toads. We demonstrate that the cardiotonic steroids in the nuchal glands of R. tigrinus are obtained from dietary toads. We further show that mothers containing high levels of bufadienolides can provision their offspring with toxins. Hatchlings had bufadienolides in their nuchal glands only if they were fed toads or were born to a dam with high concentrations of these compounds. Because geographic patterns in the availability of toxic prey are reflected in the chemical composition of the glandular fluid, snakes in toad-free regions are left undefended by steroidal toxins. Our findings confirm that the sequestration of dietary toxins underlies geographic variation in antipredatory behavior in this species and provide a unique example of sequestered defensive compounds in a specialized vertebrate structure.
亚洲蛇虎斑颈槽蛇在其颈部拥有特殊的防御腺体，其中含有被称为蟾蜍二烯羟酸内酯的甾体毒素。我们推测，虎斑颈槽蛇并不合成这些防御性甾体，而是从其作为猎物捕食的蟾蜍中获取毒素。为了验证这一假设，我们对从无蟾蜍地区和有蟾蜍地区采集的蛇的腺液进行了化学分析。我们还进行了饲养实验，用含有或不含蟾蜍的受控饮食饲养虎斑颈槽蛇幼体。我们证明，虎斑颈槽蛇颈部腺体中的强心甾体是从食用的蟾蜍中获取的。我们进一步表明，含有高浓度蟾蜍二烯羟酸内酯的母蛇能够将毒素传递给后代。只有当幼体被喂食蟾蜍或出生于体内含有高浓度这些化合物的母蛇时，它们的颈部腺体中才会含有蟾蜍二烯羟酸内酯。由于有毒猎物可获取性的地理模式反映在腺液的化学成分中，无蟾蜍地区的蛇没有甾体毒素的保护。我们的研究结果证实，摄取饮食中的毒素是该物种反捕食行为地理变异的基础，并提供了一个在特殊脊椎动物结构中摄取防御性化合物的独特例子。
