Geographic distribution of the chytrid pathogen Batrachochytrium dendrobatidis among mountain amphibians along the Italian peninsula

The amphibian chytrid pathogen Batrachochytrium dendrobatidis (Bd) is considered a major cause of amphibian population declines, particularly in montane areas. Here, we investigated the presence and distribution of Bd among populations of 3 mid- to high-altitude species spanning the entire Italian peninsula (486 individuals from 39 sites overall): the stream frog Rana italica, the fire salamander Salamandra salamandra gigliolii, and the alpine newt Mesotriton alpestris apuanus. We found Bd in all of the analyzed species. Despite the widespread distribution of the pathogen, its overall prevalence (6, 9 and 19%, respectively) was lower than previously reported for the endangered Apennine yellow-bellied toad Bombina pachypus (62.5%). Moreover, several populations of the species studied here were not infected, even at sites where Bd has been detected in other host species. When coupled with the lack of evidence for Bd-related mortalities in these species in peninsular Italy, these results suggest that mechanisms of resistance and/or tolerance are protecting populations of these species from the pathogenic activity of Bd. Nevertheless, in light of the dynamic pattern of Bd-host interactions reported in other studies, of Bd-related mortalities in at least 1 study species (S. s. salamandra) in other areas, and the ongoing climate changes in montane environments, we suggest that the occurrence of Bd should be considered a potential threat to the long-term persistence of these species, and urge the implementation of monitoring and conservation plans.