Columbia spotted frogs (Rana luteiventris) have characteristic skin microbiota that may be shaped by cutaneous skin peptides and the environment

ABSTRACT Global amphibian declines due to the fungal pathogen Batrachochytrium dendrobatidis (Bd) have led to questions about how amphibians defend themselves against skin diseases. A total of two amphibian defense mechanisms are antimicrobial peptides (AMPs), a component of amphibian innate immune defense and symbiotic skin bacteria, which can act in synergy. We characterized components of these factors in four populations of Columbia spotted frogs (Rana luteiventris) to investigate their role in disease defense. We surveyed the ability of their AMPs to inhibit Bd, skin bacterial community composition, skin metabolite profiles and presence and intensity of Bd infection. We found that AMPs from R. luteiventris inhibited Bd in bioassays, but inhibition did not correlate with Bd intensity on frogs. R. luteiventris had two prevalent and abundant core bacteria: Rhizobacter and Chryseobacterium. Rhizobacter relative abundance was negatively correlated with AMP's ability to inhibit Bd, but was not associated with Bd status itself. There was no relationship between metabolites and Bd. Bacterial communities and Bd differ by location, which suggests a strong environmental influence. R. luteiventris are dominated by consistent core bacteria, but also house transient bacteria that are site specific. Our emergent hypothesis is that host control and environmental factors shape the microbiota on R. luteiventris.

Ribeiroia ondatrae causes limb abnormalities in a Canadian amphibian community

A parasitic flatworm ( Ribeiroia ondatrae Price, 1931) is known to cause severe limb abnormalities and high mortality levels in American amphibian populations. The distributional pattern of this parasite—its main dispersal agent being birds—correlates with the boundaries of migratory flyways in the USA. Yet thus far, R. ondatrae have not been found in Canadian amphibians, which is surprising, considering that said flyways extend well into northern Canada. In this study, we report on a lake in British Columbia that is known to support amphibians with abnormalities similar to those induced by R. ondatrae. To determine if the parasite was present and if it was the cause of the abnormalities, we collected and necropsied metamorphs of the Columbia Spotted Frog ( Rana luteiventris Thompson, 1913) and the Pacific Chorus Frog ( Pseudacris regilla (Baird and Girard, 1852)), and we set up field enclosures to protect larvae from R. ondatrae. Abnormality levels were high in both species (>20%), with the vast majority being found in close proximity to the metacercariae of R. ondatrae. Moreover, the types of abnormalities closely matched those previously recorded in field and laboratory exposures of amphibians to R. ondatrae. Finally, larvae that developed in the same lake, but were protected from R. ondatrae by an enclosure, did not develop abnormalities. Collectively, these results demonstrate that R. ondatrae are both present in an amphibian community in Canada and responsible for causing limb abnormalities.