DiRenzo, G.V., Longo, A.V., Muletz-Wolz, C.R. et al. 2021. Plethodontid salamanders show variable disease dynamics in response to Batrachochytrium salamandrivorans chytridiomycosis. Biological Invasions 23: 2797-2815.. https://doi.org/10.1007/s10530-021-02536-1
Abstract
Emerging infectious diseases are among the leading drivers of the sixth mass extinction. The recent invasion of a highly pathogenic chytrid fungus, Batrachochytrium salamandrivorans (Bsal), across Europe has led to salamander mass mortality. To date, it remains unclear whether Bsal will cause salamander mass mortalities in North America. Here, we tested the Bsal susceptibility of eight wild-caught salamander species (Plethodon cinereus, P. glutinosus, P. montanus, P. cylindraceus, Desmognathus fuscus, D. wrighti, Eurycea wilderae, and Notophthalmus viridescens) by inoculating individuals sequentially with a low (10,000 zoospores) and high (500,000 zoospores) Bsal dose. Overall, we found rapid and complete mortality of N. viridescens accompanied with high-Bsal infections (> 200,000 Bsal zoospores) and severe Bsal lesions distributed across the body and deep within the skin. In contrast, we found low mortality of plethodontid salamanders, where only 5 of 60 (8%) Bsal-exposed individuals died over the course of the experiment. In general, plethodontid salamanders experienced moderate Bsal infections (~ 4000 Bsal zoospores) with small numbers of Bsal-type lesions limited to the head and lateral body. Following the first Bsal inoculation, we found that Bd co-infections negatively affected Bsal infections, suggesting cross reactivity of the immune system or competitive exclusion, but this pattern did not persist following the second inoculation. We also found that Bsal infection intensity decreased over time following the second higher Bsal inoculation, suggesting evidence of immune priming. Throughout the experiment, all species and treatments experienced stable or increasing body condition over time. Lastly, ancestral state reconstruction of Bsal susceptibility indicated that although the most recent common ancestor (MRCA) of the family Plethodontidae is resistant to Bsal, the MRCA of the genus Plethodon is tolerant of Bsal. This highlights the variation in Bsal-infection outcomes across Plethodontidae. Collectively, our results suggest that Plethodontidae salamanders differ in their Bsal susceptibility, with some species less impacted than others, which will likely have consequences for their conservation and management.