COS 213-1 - Maintaining Resistance to Batrachochytrium salamandrivorans infection despite depletion of skin defense peptides

Background/Question/Methods

Amphibian mucosal secretions contains defense compounds that can contribute to host defenses against infections and disease mitigation. Interactions between these skin defenses, such as peptides and microbes, play a vital role in the host health, development and immunological adaptations. Disease-induced population declines in amphibians are thought to be modulated by physiological and immunological responses, since some species seem to show host-level resilience toward infections. Amphibian populations worldwide have been declining due to the devastating impacts of Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal). For this experiment, we tested the influence of peptide depletion on vulnerability towards Bsal in Northern leopard frogs (Lithobates pipiens). We examined skin microbiome and peptide composition resilience towards infection. Before the experiment, the frogs were exposed to Bd as tadpoles and for the experiment exposed to two different strains of Bsal. Their peptides were depleted immediately before exposure and collected again 4 weeks after exposure to compare changes in peptide quantity and composition using micro-BCA protein for peptide quantification and MALDI-MS for composition. Skin swabs were collected before and after exposure to extract DNA for diagnostic qPCR for Bd/Bsal detection. Data was analyzed using QIIME2 and R studio.

Results/Conclusions

Our results suggest that L. pipiens did not maintained Bd infection from the tadpole stage. Peptide depletion was predicted to increase Bsal susceptibility, but this was not demonstrated; frogs did not became infected with Bsal of either strain. Instead, my results suggest a statistical difference of the frog’s peptide composition before and after Bsal exposure. We detected the antimicrobial skin peptides Brevinin-1Pa and Brevinin-1Pb among the frog’s composition. These peptides are known to have antifungal properties and help with Bd inhibition. Microbial diversity was different between the Bsal exposed frogs and controls suggesting the peptides could be modulating the microbiota towards more antifungal bacteria composition. Our microbiome results correlate with the chytrid exposure since our operational taxonomic unit showed high alpha diversity and low beta dispersion. Discovering mechanisms of resilience to disease emergence in amphibian populations is critical to conservation and disease mitigation.