Data from: Multiple stressors and the cause of amphibian abnormalities

The repeated occurrence of abnormal amphibians in nature points to ecological imbalance, yet identifying causes of these abnormalities has proved complex. Multiple studies have linked amphibian abnormalities to chemically contaminated areas, but inference about causal mechanisms is lacking. Here we use a high incidence of abnormalities in Alaskan wood frogs to strengthen inference about the mechanism for these abnormalities. We suggest that limb abnormalities are caused by a combination of multiple stressors. Specifically, toxicants lead to increased predation, resulting in more injuries to developing limbs and subsequent developmental malformations. We evaluated a variety of putative causes of frog abnormalities at 21 wetlands on the Kenai National Wildlife Refuge, south-central Alaska, USA, between 2004 and 2006. Variables investigated were organic and inorganic contaminants, parasite infection, abundance of predatory invertebrates, UVB, and temperature. Logistic regression and model comparison using the Akaike information criterion (AIC) identified dragonflies and both organic and inorganic contaminants as predictors of the frequency of skeletal abnormalities. We suggest that both predators and contaminants alter ecosystem dynamics to increase the frequency of amphibian abnormalities in contaminated habitat. Future experiments should test the causal mechanisms by which toxicants and predators may interact to cause amphibian limb abnormalities.自然界中异常两栖动物的反复出现，预示着生态失衡，但探明这些异常的成因却极为复杂。多项研究已将两栖动物异常与化学污染区域相关联，但关于其致病机制的推论仍较为匮乏。本研究以阿拉斯加林蛙（Alaskan wood frogs）的高异常发生率为研究对象，以强化对这类异常致病机制的推论。我们认为，肢体异常是多种胁迫因子共同作用的结果。具体而言，有毒物质会加剧捕食行为，进而导致发育中的肢体受到更多损伤，最终引发发育畸形。2004年至2006年间，我们在美国阿拉斯加中南部基奈国家野生动物保护区（Kenai National Wildlife Refuge）的21处湿地中，针对蛙类异常的多种假定成因开展了评估。本次评估的变量包括有机与无机污染物、寄生虫感染、捕食性无脊椎动物丰度、紫外线B（UVB）以及温度。逻辑回归与采用赤池信息准则（Akaike information criterion, AIC）的模型比较分析显示，蜻蜓以及有机、无机污染物均为骨骼异常发生频率的预测因子。我们认为，捕食者与污染物均可改变生态系统动态，进而提升污染生境中两栖动物异常的发生频率。未来的实验应验证有毒物质与捕食者如何相互作用，进而引发两栖动物肢体异常的致病机制。