Department of Zoology, Institute of Biosciences, University of São Paulo, São Paulo, São Paulo, Brazil.
Department of Biology, Notre Dame College, South Euclid, Ohio, USA.
J Exp Zool A Ecol Integr Physiol. 2022 Jun;337(5):537-546. doi: 10.1002/jez.2587. Epub 2022 Feb 24.
Sequestration of chemical defenses from dietary sources is dependent on the availability of compounds in the environment and the mechanism of sequestration. Previous experiments have shown that sequestration efficiency varies among alkaloids in poison frogs, but little is known about the underlying mechanism. The aim of this study was to quantify the extent to which alkaloid sequestration and modification are dependent on alkaloid availability and/or sequestration mechanism. To do this, we administered different doses of histrionicotoxin (HTX) 235A and decahydroquinoline (DHQ) to captive-bred Adelphobates galactonotus and measured alkaloid quantity in muscle, kidney, liver, and feces. HTX 235A and DHQ were detected in all organs, whereas only DHQ was present in trace amounts in feces. For both liver and skin, the quantity of alkaloid accumulated increased at higher doses for both alkaloids. Accumulation efficiency in the skin increased at higher doses for HTX 235A but remained constant for DHQ. In contrast, the efficiency of HTX 235A accumulation in the liver was inversely related to dose and a similar, albeit statistically nonsignificant, pattern was observed for DHQ. We identified and quantified the N-methylation of DHQ in A. galactonotus, which represents a previously unknown example of alkaloid modification in poison frogs. Our study suggests that variation in alkaloid composition among individuals and species can result from differences in sequestration efficiency related to the type and amount of alkaloids available in the environment.
化学防御物质从饮食中被隔离取决于环境中化合物的可用性和隔离机制。以前的实验表明，毒蛙体内生物碱的隔离效率存在差异，但对于潜在的机制知之甚少。本研究的目的是量化生物碱隔离和修饰对生物碱可用性和/或隔离机制的依赖程度。为此，我们给圈养繁殖的 Adelphobates galactonotus 喂食了不同剂量的海蟾蜍毒素（HTX）235A 和去氢奎宁（DHQ），并测量了肌肉、肾脏、肝脏和粪便中的生物碱含量。HTX 235A 和 DHQ 都存在于所有器官中，而 DHQ 仅以痕量存在于粪便中。对于肝脏和皮肤，两种生物碱的积累量都随着剂量的增加而增加。对于 HTX 235A，皮肤中生物碱的积累效率随着剂量的增加而增加，但对于 DHQ，效率保持不变。相比之下，HTX 235A 在肝脏中的积累效率与剂量呈反比，DHQ 也出现了类似的但统计学上不显著的模式。我们在 A. galactonotus 中鉴定并量化了 DHQ 的 N-甲基化，这代表了毒蛙中生物碱修饰的一个以前未知的例子。我们的研究表明，个体和物种之间生物碱组成的差异可能是由于环境中可用的生物碱类型和数量导致的隔离效率差异所致。
