Print PageAll species of plants and animals harbor microbial symbionts but we know very little about the specificity of microbial communities to their hosts. Few studies have compared the symbiotic microbial communities that live in or on different species of animals, and fewer still have examined animals in the wild. One potentially confounding problem is that wild species rarely directly overlap in their habitat usage and therefore it can be difficult to separate variation in microbial communities that are due to differences in environmental exposure versus innate species-specific factors. We identified pond-dwelling larval amphibian communities as a unique system to address host-specificity of skin microbial communities. Larval amphibians originate in known pond habitats and multiple species can share the same habitat spatially and temporally over the course of their development during a season, therefore they should share the same microbial inocula from the shared environment. We located four different pond habitats in unique watersheds in Colorado where multiple amphibian species were present. We sampled skin microbes from 2-4 individuals per species per pond using sterile, cotton tipped swabs. In total, 32 amphibian individuals were sampled from three different species: northern leopard frogs (Lithobates pipiens), western chorus frogs (Pseudacris triseriata), and tiger salamanders (Ambystoma tigrinum). To examine bacterial communities, we surveyed the 16S small subunit ribosomal gene using universal bacterial primers, followed by bar-coded pyrosequencing. Using bioinformatic tools including the UniFrac algorithm and QIIME, we analyzed sequence data across samples to compare the composition and relative abundance of different bacterial phylotypes. Analysis of similarity was performed to test whether host species and/or pond location were significant predictors of bacterial community variation.
Results/Conclusions
Results of the pyrosequencing allowed us to compare 745 sequences from each sample. We found that the three amphibian species differed with respect to the diversity of bacterial phylotypes present; L. pipiens had the highest diversity of bacteria and A. tigrinum the lowest. Host species was a highly significant predictor of bacterial community similarity while pond location was not significant. These results indicate that innate species differences drive the composition and abundance of skin bacterial communities on amphibians, even when different species co-habitate in the same water body. In light of recent discoveries that some bacteria on amphibian skin have demonstrated antifungal activity, these findings regarding host specificity of bacterial communities may play a role in the species-specific resistance to fungal pathogens.
