Amphibian Bacterial Communities Assemble Variably Among Host Species, Across Development, and Between Similar Habitats.

Symbiotic host-associated microbial communities are nearly ubiquitous and are often essential to host growth and development. The assembly of these communities on hosts is the result of a combination of the processes of selection, dispersal, and drift. For some species, essential symbionts are quickly acquired from the environment during embryonic development, while others may vertically acquire symbionts from parents. For amphibians with complex life cycles that undergo metamorphosis, an additional physiological transition from larval to adult forms may represent another distinct developmental window for bacterial colonization. Prior research has demonstrated that metamorphosis impacts the composition of amphibian-associated bacterial communities; however, we do not know whether similar shifts occur during metamorphosis across different amphibian species. To more clearly understand patterns in microbiome development across host species within a given area, we assessed the bacterial communities associated with eggs from five locally occurring amphibian species and tadpoles and juveniles from four of the species. Additionally, to determine if stochasticity result in varied microbiome composition among conspecifics, we raised one species, spring peepers (Pseudacris crucifer), in outdoor 1000 L mesocosms. Through 16S rRNA gene amplicon sequencing, we detected distinct bacterial communities across amphibian species and development. Additionally, we found that tadpoles harbored different communities of bacteria in the different mesocosms, suggesting that stochasticity may play a large role in bacterial assembly on tadpoles. Our results serve to deepen our understanding of natural shifts in amphibian-associated bacterial communities and how these shifts are host-species dependent. Additionally, this study provides support for the idea that stochasticity in the form of drift or priority effects can drive individual variation in microbiome composition among hosts.