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，由于宿主及其寄生虫环境的变化，出现或重新出现了许多疾病。在这项研究中，我探索了一种此类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的严重肢体畸形。其中许多畸形是由一种寄生虫(Ribeiroia Ondatrae)引起的，这种寄生虫钻进两栖幼虫发育中的四肢。然而，感染人数明显增加的原因仍不清楚。我测试了一种假设，即流入与农业和畜牧业相关的水生系统的营养物质径流是促进寄生虫感染的原因。Ribeiroia有一个复杂的生命周期，包括在蜗牛、两栖动物和鸟类之间穿梭。营养过剩(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。通过在野外研究这些关系，进行生态学实验，并使用数学模型，我调查了增加的养分输入--这是湖泊、池塘和河流的一个全球性问题--如何影响寄生虫、其宿主和畸形程度。综上所述，这些方法可能为两栖动物畸形的驱动因素提供新的见解，同时有助于推动生态系统层面的疾病研究。

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.