Patterns of disease and microbial diversity in an amphibian (Pseudacris crucifer) from the eastern United States

Background/Question/Methods

Wildlife diseases represent a significant threat to biodiversity. For example, the emergence of the fungal pathogen, Batrachochytrium dendrobatidis (Bd), has been linked to drastic reductions in amphibian diversity on a global scale. Nonetheless, some species of amphibians appear to be resistant to this pathogen. The degree of resistance shown by different species and different populations is likely due to a combination of factors, including the species composition of the microbes living on amphibian skin. These symbiotic microbes may help amphibians resist infection by producing anti-fungal metabolites and by competing for space on the skin. In North America, spring peepers (Pseudacris crucifer) are among the earliest amphibians to breed. Although they may become infected with Bd, no die-offs from Bd have been documented. In the spring of 2012, we sampled spring peepers at 10 ponds across the state of Virginia to examine patterns of Bd infection and skin microbial diversity. Additionally, 12 spring peepers from a single pond were sampled to characterize the culturable bacterial communities on their skin and the ability of these bacteria to inhibit Bd growth.

Results/Conclusions

Bd prevalence ranged from 0–88% across study ponds. Infection prevalence was related to pond water temperature, suggesting that low temperatures at the beginning of the breeding season may be outside the thermal optimum for Bd growth. Across all ponds, individual infection intensities were low (≤ 375 zoospore equivalents). We found an average of 14 (range 8–29) unique bacterial isolates on individual peepers from the site where culturable diversity was examined. Preliminary analyses indicate that these microbial symbionts are diverse, with the culturable portion of the communities representing at least 16 bacterial families and 34 genera based on sequencing of the 16S rRNA gene. Thirteen percent of all tested isolates (20/159) had anti-Bd properties (≥ 90% inhibition in growth assays). Sixty-seven percent of individual peepers (8/12) harbored at least one anti-Bd isolate. We are currently using next generation sequencing to gain a more thorough understanding of microbial diversity on the skin of peepers across Virginia and across ponds where Bd was present or absent at the time of sampling. Ultimately, we aim to understand how factors like disease influence the species composition and function of these skin microbial communities.