Collaborative Research: After the Crash: Factors Allowing Host Persistence Following Outbreaks of a Highly Virulent Disease

壶菌病是由真菌病原体水蛭壶菌（“Bd”）引起的一种新兴的两栖动物传染病，已被认为是导致世界各地两栖动物种群数量下降和灭绝的主要原因。以目前全球Bd的快速传播速度，许多两栖动物种群将在未来十年内受到感染，这可能会导致这一已经处于危险中的生物群体中大量物种灭绝。在加州内华达山脉，Bd正在以前未感染的两栖动物种群中迅速传播。山黄腿蛙（Rana muscosa）对壶菌病非常敏感，最近因感染壶菌病而导致数百个种群灭绝。有趣的是，尽管大多数寄主种群在Bd到来后灭绝，但仍有一小部分种群携带病原体持续存在，这些持续存在的种群中的疾病动态与种群崩溃期间的疾病动态根本不同。加州大学的研究人员进行这项研究的目的是了解导致这些不同疾病结果的机制。研究人员假设种群灭绝与持续存在是种群间差异的结果(1)密度依赖的疾病动力学，(2)Bd毒性，(3)青蛙易感性，或(4)环境条件。将参数化和测试一个包括宿主内Bd动态和宿主阶段结构的鼠鼠- Bd相互作用模型。此外，将使用现场和实验室实验对可能解释不同疾病结果的四种不相互排斥的假设进行检验。利用完整的Bd和青蛙基因组序列的功能基因组学方法将用于描述任何观察到的Bd毒力和/或青蛙易感性差异的遗传基础。拟议的研究将大大有助于预测未来疾病对野生动物和人类的影响。就更广泛的影响而言，研究结果将直接关系到世界范围内受疾病威胁的两栖动物的保护，并可能广泛用于为保护战略和政策举措提供信息。为了确保将结果迅速纳入这些努力，结果将通过以下方式传达给政策制定者：(i)项目研究人员继续参与红颊鼠恢复工作组，（ii）与负责红颊鼠保护的联邦和州机构（例如国家公园管理局、美国鱼类和野生动物管理局、加州渔猎部）举行年度会议，（三）与世界范围内发展两栖动物保护项目的非政府组织进行磋商。该项目将通过学生和博士后研究人员直接参与研究，促进建模、基因组学、分子遗传学、统计学、实验室和现场方法等方面的教学和培训。为了向更广泛的受众提供针对bd的培训，在该项目期间，将与两栖类专家小组（IUCN，世界自然保护联盟）合作，举办针对联邦和州机构生物学家和私人顾问的三个讲习班。抽样协议（文本和视频格式）也将以英文和西班牙文在线提供。

Chytridiomycosis is an emerging infectious disease of amphibians caused by the fungal pathogen, Batrachochytrium dendrobatidis ("Bd") that has been implicated as a major cause of amphibian population declines and extinctions around the world. At the current rapid rate of global Bd spread, many amphibian populations will become infected within the next decade, and this will likely result in substantial numbers of species extinctions in this already-imperiled group of organisms. In California's Sierra Nevada mountains, Bd is rapidly spreading through previously uninfected amphibian populations. The mountain yellow-legged frog (Rana muscosa) is highly susceptible to chytridiomycosis, and has experienced hundreds of recent population extinctions due to Bd infection. Interestingly, although the majority of host populations are driven extinct following the arrival of Bd, a small fraction of populations persist with the pathogen, and disease dynamics in these persistent populations are fundamentally different from those during population crashes. The goal of this research by researchers from University of California is to understand the mechanisms leading to these contrasting disease outcomes. The investigators hypothesize that population extinction versus persistence is the result of between-population differences in (1) density-dependent disease dynamics, (2) Bd virulence, (3) frog susceptibility, or (4) environmental conditions. A model of the R. muscosa- Bd interaction that includes within-host Bd dynamics and host stage-structure will be parameterized and tested. In addition, four non-mutually exclusive hypotheses that could account for different disease outcomes will be tested using field and laboratory experiments. A functional genomics approach that utilizes complete Bd and frog genome sequences will be used to describe the genetic basis of any observed differences in Bd virulence and/or frog susceptibility. The proposed research will contribute significantly to the ability to predict outcomes of future diseases on wildlife and human populations. In terms of broader impacts, results from the research will be directly relevant to the conservation of amphibians worldwide that are threatened by disease, and will likely be broadly used to inform conservation strategies and policy initiatives. To ensure the rapid incorporation of results into such efforts, results will be communicated to policy makers via (i) continued participation by project researchers in an R. muscosa recovery working group, (ii) annual meetings with federal and state agencies charged with R. muscosa conservation (e.g., National Park Service, U. S. Fish and Wildlife Service, California Department of Fish and Game), and (iii) consultation with non-governmental organizations developing amphibian conservation programs worldwide. The project will promote teaching and training of a diverse group of students and postdoctoral researchers in modeling, genomics, molecular genetics, statistics, and laboratory and field methods through their direct involvement in the research. To provide Bd-specific training to a wider audience, three workshops targeted at federal and state agency biologists and private consultants will be hosted during the project in collaboration with the Amphibian Specialist Group (IUCN, World Conservation Union). Sampling protocols (in text and video formats) will also be provided online in both English and Spanish.