Linking Ecology, Physiology and Human Land Use: The Impact of Environmental Stress on Disease Susceptibility in Larval Amphibians

了解传染病在自然群落中的作用是群落生态学中的一个关键问题。寄主-病原体的相互作用可能比其他类型的相互作用(例如捕食者-猎物和竞争)更重要，在很大程度上由宿主的生理条件决定。为了预测感染对宿主种群动态的影响，需要对宿主生理学和免疫学有详细的了解。淡水湿地是蜗牛的主要栖息地，是包括双基因吸虫在内的各种蠕虫寄生虫的中间宿主。吸虫每年导致数十万例人类疾病(例如血吸虫病)，并与两栖动物的发育异常有关。两栖动物畸形，特别是与肢体发育有关的畸形，现在已在整个北美被报道。畸形的广泛性质和流行程度的明显增加引起了科学家和公众的极大兴趣。虽然初步的实验室实验表明，吸虫感染会导致一些畸形，但研究人员指出，需要更多的实地工作来评估这种联系在自然界中的相关性。此外，一些研究表明，湿地土地利用的变化，如富营养化加剧和水文变化，可能会通过增加中间宿主(蜗牛)的数量而导致畸形的爆发。我们建议研究寄主对土地利用变化(环境压力)的激素反应在调节疾病易感性方面的作用。拟议的项目将补充正在进行的一项研究，该研究旨在研究土地利用变化如何影响蜗牛(中间宿主)的数量，从而影响两栖动物感染率。这一建议将大大增加我们对自由生活的动物如何对人为土地利用变化做出生理反应的知识，而产生的关于宿主易感性的数据将显著增加对这个宿主/寄生虫系统中疾病爆发的预测模型的发展。

Understanding the role that infectious diseases play in natural communities is a key question in community ecology. Host-pathogen interactions, perhaps more so than other types of interactions (e.g. predator-prey & competition), are largely determined by the physiological condition of the host. To gain a predictive understanding of the impact that infection may have on host population dynamics requires a detailed understanding of host physiology and immunology. Freshwater wetlands are primary habitat for snails serving as intermediate hosts for a variety of helminthic parasites including digenetic trematodes. Trematodes are responsible for hundreds of thousands of cases of human disease each year (e.g., schistosomiasis) and have been linked with developmental abnormalities in amphibians. Amphibian deformities, in particular those related to limb development, have now been reported throughout North America. The widespread nature and apparent increase in the prevalence of deformities has lead to substantial interest from scientists and the general public. While preliminary laboratory experiments suggest that infection by trematodes can cause some deformities, researchers have pointed out that there is a need for more fieldwork to evaluate the association in nature. In addition, some research has suggested that land use changes in wetlands, such as increased eutrophication and altered hydrology, may precipitate outbreaks of deformities by increasing abundance of intermediate hosts (snails). We propose to examine the role of the host's hormonal response to land use changes (environmental stress) in terms of how it can regulate disease susceptibility. The proposed project will complement an ongoing study examining how land use changes affect snail (intermediate host) abundance and therefore influence amphibian infection rates. This proposal will add significantly to our knowledge of how free-living animals respond physiologically to anthropogenic land use changes, and the data generated on host susceptibility will add significantly to the development of a predictive model for disease outbreak in this host/parasite system.