Date of Award

2018

Document Type

Thesis

Degree Name

Bachelor of Science

Department

Biology

Abstract

Research on the amphibian pathogen Batrachochytrium dendrobatidis (Bd), the causative agent of the lethal disease chytridiomycosis, has advanced from assessments of pathogenicity and species susceptibility to more specialized questions concerning the complex interactions between the pathogen, species-specific immune responses, and the environment. Our work examines the potential for interactions between the two most important innate immune defenses of frogs against Bd: secretions of antimicrobial peptides and communities of commensal cutaneous bacteria. While both defenses have been studied individually, little data are available to examine interactions between these defenses. We conducted our study with field captured Panamanian glass frogs (Espadarana prosoblepon) and used a norepinephrine injection to induce a stress response and the release of peptides in skin secretions. We quantified the peptides from these secretions using an altered BCA assay. We also collected samples of cutaneous bacteria before and after injection to determine if the bacterial community changed after exposure to skin secretions. We used the bacteria samples to isolate and purify unique bacterial types based on colony morphology, then used challenge assays to understand the effect of isolated bacterial types on Bd growth in vitro. We also exposed several of the isolated bacteria to the skin peptides to analyze their susceptibility to inhibition to the peptide. We found that the overall amount of culturable cutaneous bacterial morphotypes decreased after the frogs were injected, although we did not observe a statistical difference in the amount of peptides secreted from saline and norepinephrine injected frogs. Every bacterial species we collected inhibited Bd growth to some degree, which is a higher proportion than typically found in previous studies. Growth in the presence of the frog skin peptides for three bacteria was dependent on the morphotype, which is indicative of different individual molecular interactions. Overall, these data provide useful information for the developing conceptualization of the Bd-host system, which can assist conservationists in preparing the most effective course of action in preventing disease-induced amphibian declines.

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