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

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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.