Reorganization of bacterial community network structure in the eastern redback salamander (Plethodon cinereus) and its soil reservoir across a gradient of land use.

The eastern redback salamander Plethodon cinereus is prevalent in the urbanized northeastern USA and exhibits low susceptibility to the fungal pathogen Batrachochytrium dendrobatidis (Bd). Disease resistance is partially attributed to Bd-inhibitory microbes in the P. cinereus cutaneous microbiome, but less is known regarding the associations that structure these bacterial communities. This is an essential area of study as shifts in microbial associations may influence community stability and function, driving differences in disease tolerance. Here, we analyzed the networks of the soil and salamander skin core bacterial communities along a 65-km urbanization gradient originating in New York City. We leveraged network analysis tools that help account for the biases inherent in 16S rRNA amplicon datasets, finding that soil networks were the most complex and stable, but complexity and stability increased with urbanization intensity in salamander networks. The network of Bd-positive salamanders was also more complex and stable than that of Bd-negative salamanders. While stress and complexity are thought to be destabilizing, our results suggest that prolonged exposure to environmental degradation may promote larger, stable co-occurring populations of microbes on hosts. This network analysis work generated hypotheses with experimental applicability, ultimately having the potential to enhance conservation management efforts.