Disease prevalence within natural populations is increasing and some research suggests that this may be due to the influence of human activities. Amphibian populations are particularly susceptible to disease and anthropogenic influence (i.e. chemical use), with such stressors acting as two major contributors to amphibian declines across the globe. Importantly, the amphibian skin harbors diverse communities of microbes that are highly interactive with the environment, providing the initial defense against external stressors. Utilizing holistic approaches that characterize responses of both hosts and their microbial symbionts to environmental shifts are imperative to understand the effects of stressors on overall host health. Using the northern leopard frog (Lithobates pipiens) as our model, we investigated the effects of a common trematode (family Echinostomatidae), a common agricultural antimicrobial (Sulfadimethoxine; SDM), and their interaction on amphibian skin microbiota (i.e. alpha and beta diversity) and amphibian health (i.e. growth metrics and susceptibility to parasites).
Results/Conclusions
In the trematode-exposed individuals, we noted an increase in alpha diversity and a shift in microbial communities. In the SDM treated individuals, we found a change in the composition of the skin microbiota similar to those induced by the trematode treatment. Groups treated with SDM, echinostomes, or a combination of SDM and echinostomes, had higher relative abundances of OTUs assigned to Flavobacterium and Acinetobacter. Both of these genera have been associated with infectious disease in amphibians and the production of anti-pathogen metabolites. Similar changes in microbial community composition between SDM and trematode exposure individuals may have resulted from stress-related disruption of host immunity. Despite changes in the microbiota, we found no effect of echinostomes and SDM on host health. We have shown that a parasite and contaminant may impose changes on the microbiota despite an absence of influence on host health. Given the current disease- and pollution-related threats facing amphibians, holistically characterizing the response of hosts and their microbial symbionts to common stressors will allow further understanding of microbial ecology in our changing world.