Amphibian Mucosal Defenses against an Emerging Fungal Disease: Testing for Selection in Recovering Populations

如今，两栖动物被认为是世界上最受威胁的脊椎动物类别。除了栖息地丧失之外，新出现的传染病(EID)是全球两栖动物数量下降的主要原因之一。最具灾难性的两栖动物宰牲节是由壶菌巴氏杆菌(Bd)引起的壶菌病。水生游动孢子穿透两栖动物皮肤，在表皮细胞内发育成孢子囊，释放出新的游动孢子。已经证明，这种真菌对热、冷和干旱都很敏感。因此，它在热带高原地区特别流行，气候持续凉爽潮湿，导致整个两栖动物群落大规模下降。在巴拿马，与壶菌病有关的发病率在1990年代初首次出现下降。此后，疫情沿着巴拿马中部山脉从西向东呈波浪状蔓延。有观点认为，疾病暴发后，与溪流相关的高原物种可能已经灭绝。然而，在最近的田野调查中，已经重新发现了与壶类相关的、有充分记录的下降的单身种群，其中一些甚至显示出个体数量的增加。然而，一些物种和种群恢复的原因仍然鲜为人知。初步研究表明，由特异性抗菌肽(AMPs)、抗体和微生物次级代谢物组成的两栖动物联合免疫防御系统对Bd的有效性可能因物种和种群而异。一般来说，具有水生蝌蚪阶段的山地物种在Bd流行期间更有可能衰落，无论它们的分类归属如何。相反，疾病相关种群减少后的种群恢复只在特定的类群中观察到。本研究的主要目的是测试自然选择是否导致持续存在的两栖动物种群对Bd的更高抵抗力，以及表型可塑性是否影响两栖动物黏膜对Bd的粘液体功能。因此，将在不同海拔和不同接触病原体时间的几个种群中测试粘液体对Bd的功能。此外，还将测试青蛙是否已经在蝌蚪阶段收到了它的益生菌皮肤微生物。此外，还将在迁地繁育计划中测试温度和光照等环境参数是否会影响人工饲养的两栖动物的粘液体功能。

Nowadays, amphibians are considered the most threatened vertebrate class worldwide. Besides habitat loss, Emerging Infectious Diseases (EIDs) are among the main causes for a worldwide decline in amphibian populations. The most disastrous amphibian EID is chytridiomycosis, caused by the Chytrid fungus Batrachochytrium dendrobatidis (Bd). The waterborne zoospore penetrates the amphibian skin and develops inside epidermal cells to sporangia that release new zoospores. It has been shown that the fungus is susceptible to heat, cold, and drought. Thus, it is especially epidemic in tropical highland situations with a constant cool and humid climate, where it has caused mass declines of whole amphibian communities. In Panama, chytridiomycosis related declines were first observed in the early 1990. Since then, the epidemic is spreading in a wave-like pattern from west to east along the Panamanian central mountain range. It has been proposed that stream associated highland species might have been extinct after disease outbreak. However, single populations that had suffered from chytrid related, well-documented declines have been rediscovered during recent field work, some of which even show an increase in numbers of individuals. However, the reasons why some species and populations recover are still poorly understood. Preliminary studies have shown that the effectiveness against Bd of the combined amphibian immune defense, consisting of specific antimicrobiotic peptides (AMPs), antibodies, and microbiotic secondary metabolites, may vary among species and populations. Generally, mountainous species with an aquatic tadpole stage are more likely to decline during Bd epidemics, irrespective of their taxonomic affiliation. On the contrary, population recovery following disease related population declines has been only observed in particular taxa.The main goals of this research project are to test if natural selection has led to a higher resistance of persisting amphibian populations against Bd and if phenotypic plasticity influences mucosome function of the amphibian mucosa against Bd respectively. Therefore, the mucosome function against Bd will be tested in several populations with different exposure time to the pathogen and at different altitudes. Further, it will be tested if the frog receives its probiotic skin microbiom already in the tadpole stage. In addition, it will be tested if environmental parameters like temperature and illumination have an effect on mucosome function of captive bred amphibians in ex-situ breeding programs.