Department of Biology, Stanford University, Stanford, California, United States of America.
Center for Systems Biology, Harvard University, Cambridge, Massachusetts, United States of America.
PLoS One. 2018 Dec 26;13(12):e0207940. doi: 10.1371/journal.pone.0207940. eCollection 2018.
Poison frogs acquire chemical defenses from the environment for protection against potential predators. These defensive chemicals are lipophilic alkaloids that are sequestered by poison frogs from dietary arthropods and stored in skin glands. Despite decades of research focusing on identifying poison frog alkaloids, we know relatively little about how environmental variation and subsequent arthropod availability impacts alkaloid loads in poison frogs. We investigated how seasonal environmental variation influences poison frog chemical profiles through changes in the diet of the Climbing Mantella (Mantella laevigata). We collected M. laevigata females on the Nosy Mangabe island reserve in Madagascar during the wet and dry seasons and tested the hypothesis that seasonal differences in rainfall is associated with changes in diet composition and skin alkaloid profiles of M. laevigata. The arthropod diet of each frog was characterized into five groups (i.e. ants, termites, mites, insect larvae, or 'other') using visual identification and cytochrome oxidase 1 DNA barcoding. We found that frog diet differed between the wet and dry seasons, where frogs had a more diverse diet in the wet season and consumed a higher percentage of ants in the dry season. To determine if seasonality was associated with variation in frog defensive chemical composition, we used gas chromatography / mass spectrometry to quantify alkaloids from individual skin samples. Although the assortment of identified alkaloids was similar across seasons, we detected significant differences in the abundance of certain alkaloids, which we hypothesize reflects seasonal variation in the diet of M. laevigata. We suggest that these variations could originate from seasonal changes in either arthropod leaf litter composition or changes in frog behavioral patterns. Although additional studies are needed to understand the consequences of long-term environmental shifts, this work suggests that alkaloid profiles are relatively robust against short-term environmental perturbations.
毒蛙从环境中获得化学防御来保护自己免受潜在捕食者的侵害。这些防御性化学物质是亲脂性生物碱，毒蛙从饮食中的节肢动物中摄取并储存在皮肤腺中。尽管几十年来的研究一直致力于确定毒蛙生物碱，但我们对环境变化和随后的节肢动物可利用性如何影响毒蛙生物碱负荷知之甚少。我们通过研究攀爬曼塔雷（Mantella laevigata）的饮食变化来研究季节性环境变化如何影响毒蛙的化学特征。我们在马达加斯加的 Nosy Mangabe 岛保护区收集了潮湿和干燥季节的雌性 M. laevigata，并测试了一个假设，即降雨量的季节性差异与 Mantella laevigata 的饮食组成和皮肤生物碱特征的变化有关。使用视觉鉴定和细胞色素氧化酶 1 DNA 条形码，将每只青蛙的节肢动物饮食分为五个组（即蚂蚁、白蚁、螨虫、昆虫幼虫或“其他”）。我们发现，青蛙的饮食在潮湿和干燥季节之间存在差异，在潮湿季节，青蛙的饮食更为多样化，而在干燥季节，它们消耗的蚂蚁比例更高。为了确定季节性是否与青蛙防御性化学成分的变化有关，我们使用气相色谱/质谱法从个体皮肤样本中定量生物碱。尽管识别出的生物碱种类在季节之间相似，但我们检测到某些生物碱的丰度存在显著差异，我们假设这反映了 M. laevigata 饮食的季节性变化。我们认为这些变化可能源于节肢动物落叶组成的季节性变化或青蛙行为模式的变化。尽管需要进一步的研究来了解长期环境变化的后果，但这项工作表明，生物碱特征对短期环境干扰相对稳健。
