Amphibians decline in peninsular Italy: is the chytrid pathogen Batrachochytrium dendrobatidis playng a role?
Author(s)
Zampiglia, Mauro
Date Issued
June 12, 2013
Type
Doctoral Thesis
Abstract
In the last decades, severe declines of amphibian populations have been observed worldwide and the extinction of many species has been reported. Among the possible causes leading to these declines, an emerging infectious disease, chytridiomycosis, is considered a main driver. In peninsular Italy, population declines of several species have been reported, especially the endemic yellow-bellied toad Bombina pachypus. Nonetheless, no studies have to date investigated the distribution and abundance of the chytrid fungus Batrachochytrium dendrobatidis, the aetiological agent of chytridiomycosis, along the Italian peninsula, as well as its role in the observed declines. Here we analysed the geographic distribution and prevalence of B. dendrobatidis among populations of 4 Apennine endemic amphibians, including the highly endangered B. pachypus. B. dendrobatidis appeared widespread among B. pachypus populations throughout its range. Moreover we found evidence that it was already common in this area since at least the end of 1970s, i.e. long before the earliest evidence of decline for this species. Thus, while a link between B. dendrobatidis infections and B. pachypus population declines appeared plausible, we suggests that it did not acted as a ‘lone killer’, but in conjunction with other factors. By analyzing the spatial and temporal patterns of B. dendrobatidis abundance, of B. pachypus demographic trend, and of several putative co-factors, we identified the recent climate change and the genetic diversity of host populations as the most likely conspirators. We forecasted the potential impact of the predicted climate change (to 2080) on B.pachypus populations, under a range of emission scenarios. A drastic reduction of habitat suitability was predicted in the southern area, that is the area hosting the hotspot of intraspecific genetic variability for this species and the only area where demographically stable populations have been reported. Accordingly, B. pachypus was predicted to lose most of its potential to respond adaptively to future environmental changes and other threats, such as diseases. On the other hand, northern areas ware predicted to increase their suitability for the species. Thus, as a urgent conservation action, we proposed restocking programs aimed at increasing the genetic variability - and possibly diseases tolerance - of northern populations using the (currently available) southern resources. To assess the consistence of the observed patterns across multiple species, we analysed the pattern of chytrid occurrence among populations of the montane species Salamandra salamandra gigliolii, Rana italica and Mesotriton alpestris apuanus. While B. dendrobatidis was widespread among these species as well, overall prevalence was significantly lower than that observed in B. pachypus, and we found no firm evidence for chytrid-related declines in these
species, suggesting that mechanisms of resistance or tolerance are warding populations of these species from pathogenic activity. On the whole, our results showed differential responses of host species and populations to the chytrid pathogen, highlighting the importance of considering the
host x pathogen x environment interactions in the study of disease dynamics.
Additional information
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche
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