Texas Parks and Wildlife Department, Austin, TX, USA.
US Fish and Wildlife Service, Honolulu, HI, USA.
Glob Chang Biol. 2018 Jan;24(1):e275-e288. doi: 10.1111/gcb.13908. Epub 2017 Oct 19.
Widespread observations of malformed amphibians across North America have generated both concern and controversy. Debates over the causes of such malformations-which can affect >50% of animals in a population-have continued, likely due to involvement of multiple causal factors. Here, we used a 13-year dataset encompassing 53,880 frogs and toads from 422 wetlands and 42 states in the conterminous USA to test hypotheses relating abnormalities and four categories of potential drivers: (i) chemical contaminants, (ii) land use practices, (iii) parasite infection, and (iv) targeted interactions between parasites and pesticides. Using a hierarchically nested, competing-model approach, we further examined how these associations varied spatially among geographic regions. Although malformations were rare overall (average = 1.6%), we identified 96 hotspot sites with 5%-25% abnormal individuals. Using the full dataset of 934 collections (without data on parasite infection), malformation frequency was best predicted by the presence of oil and gas wells within the watershed. Among collections also examined for parasite infection (n = 154), average parasite load and its interaction with pesticide application positively predicted malformations: wetlands with a greater abundance of the trematode Ribeiroia ondatrae were more likely to have malformed amphibians, but these effects were strongest when pesticide application was also high, consistent with prior experimental research. Importantly, however, the influence of these factors also varied regionally, helping explain divergent results from previous studies at local scales; parasite infection was more influential in the West and Northeast, whereas pesticide application and oil/gas wells correlated with abnormalities in the Northeast, Southeast, and western regions of the USA. These results, based on the largest systematic sampling of amphibian malformations, suggest that increased observations of abnormal amphibians are associated with both parasite infection and chemical contaminants, but that their relative importance and interaction strength varied with the spatial extent of the analysis.
北美洲广泛观察到畸形两栖动物，这引起了人们的关注和争议。关于这种畸形的原因的争论一直在持续，这些畸形可能会影响到一个种群中超过 50%的动物，这可能是由于涉及多个因果因素。在这里，我们使用了一个包含 13 年数据的数据集，该数据集涵盖了来自美国大陆 42 个州的 422 个湿地的 53880 只青蛙和蟾蜍，以检验与异常相关的四个假设和四个潜在驱动因素类别：(i) 化学污染物，(ii) 土地利用实践，(iii) 寄生虫感染，以及 (iv) 寄生虫和农药之间的靶向相互作用。使用层次嵌套的竞争模型方法，我们进一步研究了这些关联在地理区域之间的空间变化。尽管整体畸形率较低（平均值为 1.6%），但我们发现了 96 个热点地区，其中有 5%-25%的异常个体。在使用包含 934 个采集样本（无寄生虫感染数据）的完整数据集时，畸形频率最好由流域内的石油和天然气井的存在来预测。在也检查了寄生虫感染的采集样本中（n=154），平均寄生虫负荷及其与农药应用的相互作用正向预测了畸形：具有更多圆口螺属吸虫 Ribeiroia ondatrae 的湿地更有可能有畸形的两栖动物，但当农药应用也很高时，这些影响最强，这与先前的实验研究一致。然而，重要的是，这些因素的影响也因地区而异，有助于解释以前在局部尺度上的研究的分歧结果；寄生虫感染在西部和东北部更为重要，而农药应用和石油/天然气井与美国东北部、东南部和西部的异常相关。这些基于对最大规模的两栖动物畸形系统抽样的结果表明，观察到异常两栖动物的增加与寄生虫感染和化学污染物都有关，但它们的相对重要性和相互作用强度因分析的空间范围而异。
