Many organisms synthesize secondary metabolites against natural enemies. However, to which environmental factors the production of these metabolites is adjusted to is poorly investigated in animals, especially so in vertebrates. Bufadienolides are steroidal compounds that are present in a wide range of plants and animals and, if present in large quantities, can provide protection against natural enemies, such as pathogens. In a correlative study involving 16 natural populations we investigated how variation in bufadienolide content of larval common toads (Bufo bufo) is associated with the bacterial community structure of their aquatic environment. We also evaluated pond size, macrovegetation cover, and the abundance of predators, conspecifics and other larval amphibians. We measured toxin content of tadpoles using HPLC-MS and determined the number of bufadienolide compounds (NBC) and the total quantity of bufadienolides (TBQ). AICc-based model selection revealed strong relationships of NBC and TBQ with bacterial community structure of the aquatic habitat as well as with the presence of conspecific tadpoles. The observed relationships may have arisen due to adaptation to local bacterial communities, phenotypic plasticity, differential biotransformation of toxin compounds by different bacterial communities, or a combination of these processes. Bacterial groups that contribute to among-population variation in toxin content remain to be pinpointed, but our study suggesting that toxin production may be influenced by the bacterial community of the environment represents an important step towards understanding the ecological and evolutionary processes leading to microbiota-mediated variation in skin toxin profiles of aquatic vertebrates.

中文翻译：

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普通蟾蜍（Bufo bufo）蝌蚪的化学防御与其自然水生栖息地的细菌群落结构之间的关系。


许多生物体合成次生代谢物来对抗天敌。然而，在动物中，特别是在脊椎动物中，对这些代谢物的产生会根据哪些环境因素进行调整的研究很少。蟾蜍二烯内酯是存在于多种植物和动物中的甾体化合物，如果大量存在，可以提供针对天敌（例如病原体）的保护。在一项涉及 16 个自然种群的相关研究中，我们研究了常见蟾蜍 ( Bufo bufo ) 幼虫的蟾蜍二烯内酯含量变化与其水生环境的细菌群落结构之间的关系。我们还评估了池塘大小、大型植被覆盖度以及捕食者、同种动物和其他两栖动物幼体的丰度。采用HPLC-MS测定蝌蚪的毒素含量，并测定蟾蜍二烯内酯化合物的数量（NBC）和蟾蜍二烯内酯的总量（TBQ）。基于 AICc 的模型选择揭示了 NBC 和 TBQ 与水生栖息地的细菌群落结构以及同种蝌蚪的存在之间的密切关系。观察到的关系可能是由于对当地细菌群落的适应、表型可塑性、不同细菌群落对毒素化合物的差异生物转化或这些过程的组合而产生的。导致种群间毒素含量变化的细菌群仍有待查明，但我们的研究表明，毒素的产生可能受到环境细菌群落的影响，这代表着理解导致微生物群介导的生态和进化过程的重要一步。水生脊椎动物皮肤毒素特征的变化。