DISSERTATION RESEARCH: Ecosystem Drivers of Disease Emergence: Linking Aquatic Eutrophication and Amphibian malformations

寄生虫和病原体是大多数生态系统中最常见的成员之一，影响着群落结构、食物网甚至进化。 然而，近几十年来，许多疾病出现或重新出现，往往是由于宿主及其寄生虫的环境发生变化。 在这项研究中，我探讨了这种疾病的直接和间接原因-在北美两栖动物种群中广泛观察到严重的肢体畸形。 许多这些畸形是由一种寄生虫（Ribeiroia ondattera）引起的，这种寄生虫会钻入两栖动物幼虫发育中的四肢。 然而，感染明显增加的原因仍不清楚。 我测试的假设，营养径流到水生系统与农业和养牛生产是负责促进寄生虫感染。 Ribeiroia有一个复杂的生命周期，涉及蜗牛，两栖动物和鸟类之间的通道。 过量的营养（富营养化）预计会增加支持寄生虫的蜗牛数量，导致两栖动物中更多的寄生虫，从而导致更多的畸形。 通过研究这些关系在现场，进行生态实验，并使用数学模型，我调查如何增加营养投入-一个全球性的问题，在湖泊，池塘和河流-影响寄生虫，其主机，和畸形的水平。 总之，这些方法可以为两栖动物畸形的驱动因素提供新的见解，同时有助于推进疾病研究的生态系统水平方法。

Parasites and pathogens are among the most common members of most ecosystems and influence community structure, food webs, and even evolution. In recent decades, however, numerous diseases have emerged or re-emerged, frequently owing to changes in the environment of hosts and their parasites. In this study, I explore the direct and indirect causes of one such disease - widespread observations of severe limb deformities in North American amphibian populations. Many of these malformations are caused by a parasite (Ribeiroia ondatrae) that burrows into the developing limbs of larval amphibians. However, reasons for the apparent increase in infection remain unclear. I test the hypothesis that nutrient runoff into aquatic systems associated with agriculture and cattle production is responsible for promoting parasite infection. Ribeiroia has a complex life cycle involving passage among snails, amphibians, and birds. Excess nutrients (eutrophication) are expected to increase the numbers of snails that support the parasite, leading to more parasites in amphibians and therefore more deformities. By studying these relationships in the field, conducting ecological experiments, and using mathematical models, I investigate how increased nutrient inputs - a global problem in lakes, ponds, and rivers - affect the parasite, its hosts, and the level of deformities. Taken together, these approaches may offer new insights into the drivers of amphibian malformations while helping to advance an ecosystem-level approach to the study of disease.