Weathering the storm: legacies of extreme meteorological events and daily weather variability shape the skin microbiota of the endangered golden Alpine salamander Salamandra atra aurorae (Trevisan, 1982)

Ecosystems worldwide are undergoing unprecedented changes, and as a result amphibians are experiencing devastating population declines driven by subsequent habitat loss and emerging pathogens. The skin microbiota is an important first line of defence for amphibians against pathogens. Here, for the first time, we characterised the bacteria and fungi comprising the skin microbiota of 56 individual golden Alpine salamanders (Salamandra atra aurorae, Trevisan, 1982), a highly endemic and endangered amphibian subspecies. In addition, we investigated the impact of the 2018 Vaia windstorm on skin microbiota of salamanders in plots classified as impacted or non-impacted based on windthrows. Salamander sex, weather during sampling, and dominant tree species in plots were also investigated as influencers of microbiota. Beta diversity estimates revealed greater variation in bacterial microbiota composition among individuals from non-impacted plots compared to plots impacted by Vaia. Notably, we found differential abundances of five genera of bacteria and eight genera of fungi in the skin microbiota of salamanders from impacted compared with non-impacted plots. Further analyses revealed that median relative abundances of Aeromonas hydrophila, the causative agent of the potentially fatal red-leg syndrome, were significantly higher in microbiota of salamanders from impacted plots. Weather conditions during sampling significantly influenced both alpha and beta diversity of the skin microbiota, and explained up to 9% of bacterial and 6% of fungal variation. Bacterial richness and phylogenetic diversity were lower during rainfall, whereas fungal beta diversity increased, suggesting contrasting moisture preferences. These findings suggest that extreme weather events, as well as moderate daily weather fluctuations, may be associated with the microbial communities of amphibian skin, potentially affecting their resilience to pathogens. This study underscores the importance of considering both natural and human-mediated disturbances in conservation strategies for vulnerable species like the golden Alpine salamander.