Carotenoids and amphibians: effects on life history and susceptibility to the infectious pathogen, Batrachochytrium dendrobatidis

Carotenoids are considered beneficial nutrients because they provide increased immune capacity. Although carotenoid research has been conducted in many vertebrates, little research has been done in amphibians, a group that is experiencing global population declines from numerous causes, including disease. We raised two amphibian species through metamorphosis on three carotenoid diets to quantify the effects on life-history traits and post-metamorphic susceptibility to a fungal pathogen (Batrachochytrium dendrobatidis; Bd). Increased carotenoids had no effect on survival to metamorphosis in gray treefrogs (Hyla versicolor) but caused lower survival to metamorphosis in wood frogs [Lithobates sylvaticus (Rana sylvatica)]. Increased carotenoids caused both species to experience slower development and growth. When exposed to Bd after metamorphosis, wood frogs experienced high mortality, and the carotenoid diets had no mitigating effects. Gray treefrogs were less susceptible to Bd, which prevented an assessment of whether carotenoids could mitigate the effects of Bd. Moreover, carotenoids had no effect on pathogen load. As one of only a few studies examining the effects of carotenoids on amphibians and the first to examine potential interactions with Bd, our results suggest that carotenoids do not always serve amphibians in the many positive ways that have become the paradigm in other vertebrates.

类胡萝卜素（Carotenoids）被视为有益营养素，因其能够提升机体免疫能力。尽管已有诸多针对脊椎动物的类胡萝卜素相关研究，但针对两栖动物的相关探索仍较为匮乏——两栖动物种群正因包括疾病在内的诸多因素面临全球性衰退。我们通过三种类胡萝卜素日粮完成了两种两栖动物的变态发育饲养实验，以量化其对生活史性状以及变态后个体对真菌病原体蛙壶菌（Batrachochytrium dendrobatidis; Bd）的易感性的影响。在灰树蛙（Hyla versicolor）中，类胡萝卜素摄入增加对其变态前存活率无显著影响，但会降低林蛙[Lithobates sylvaticus (Rana sylvatica)]的变态前存活率。类胡萝卜素摄入增加会导致两种两栖动物的发育与生长速率均有所减缓。变态后暴露于蛙壶菌环境时，林蛙出现了高死亡率，而类胡萝卜素日粮未表现出缓解效应。灰树蛙对蛙壶菌的易感性较低，因此无法评估类胡萝卜素是否能够缓解蛙壶菌的危害。此外，类胡萝卜素对病原体负荷无显著影响。作为少数探讨类胡萝卜素对两栖动物影响的研究之一，且是首个考察其与蛙壶菌潜在交互作用的研究，我们的结果表明，类胡萝卜素并非总能如其他脊椎动物研究中所确立的范式那样，对两栖动物发挥诸多有益作用。