Landscape and water characteristics correlate with immune defense traits across Blanchard's cricket frog (Acris blanchardi) populations

Due to ease of global transportation, disease threats to amphibians are expected to increase. Therefore it is crucial that we improve our understanding of factors which may depress disease resistance so that we can incorporate this information into long-term conservation planning. Amphibians are protected from disease-causing pathogens by two skin-associated immune defense traits: the skin microbiome and the antimicrobial peptides found within natural peptide secretions (NPS) produced by the skin. Particular environmental characteristics may alter these amphibian immune defense traits and potentially affect disease resistance. We surveyed the skin-associated microbial communities (microbiome) and natural peptide secretions (NPS) of Blanchard's cricket frogs (Acris blanchardi), at each of eleven sites across the species' declining range. We utilized an AICc model selection and model averaging approach to test for potential environmental influence on these traits. We found that populations differed in microbiomes and NPS production, but not NPS bioactivity against Bd (Batrachochytrium dendrobatidis). The microbiome was associated with water conductivity, ratio of natural to managed land, and latitude. Additionally the microbiome was affected by interactions between frog sex and latitude, between frog sex and water surface area, and between the ratio of natural to managed land and water surface area. NPS production was influenced by an interaction between water surface area and conductivity. We found no evidence that NPS influence the microbiome; however, Bd growth rate in culture was positively associated with NPS production. This study indicates that environmental characteristics influence amphibian immune defense traits and may explain population differences in pathogen resistance.