Abstract
The emerging amphibian disease, Batrachochytrium dendrobatidis (Bd), is driving population declines worldwide and even species extinctions in Australia, South and Central America. In order to mitigate effects of Bd on amphibian populations, high-exposed areas should be identified at the local scale and effective conservation measures should be planned at the national level. This assessment is actually lacking in the Mediterranean basin, and in particular in Italy, one of the most relevant amphibian diversity hotspots in the entire region. In this study, we reviewed the available information on Bd in Italy, and conducted a 5-year molecular screening on 1274 individual skin swabs belonging to 18 species. Overall, we found presence of Bd in 13 species and in a total of 56 known occurrence locations for peninsular Italy and Sardinia. We used these occurrence locations and climate data to model habitat suitability of Bd for current and future climatic scenarios. We then employed electric circuit theory to model landscape permeability to the diffusion of Bd, using a resistance map. With this procedure, we were able to model, for the first time, the diffusion pathways of Bd at the landscape scale, characterising the main future pathways towards areas with a high probability of Bd occurrence. Thus, we identified six national protected areas that will become pivotal for a nationally-based strategic plan in order to monitor, mitigate and possibly contrast Bd diffusion in Italy.
Highlights
As part of the recent "biodiversity crisis," many amphibian populations are declining worldwide (e.g., Blaustein et al 1994; Wake and Vredenburg 2008; Catenazzi 2015; Scheele et al 2019)
The present research does not focus on individual Batrachochytrium dendrobatidis (Bd) load, in general the Bd load obtained by qPCR ranged from 1 to 140 Bd genome equivalents (Bd GE) per swab, which may be considered as a relatively low infection load
We obtained 23 original occurrence locations in different parts of peninsular Italy to be added to bibliographic data, yielding to a total of 56 Bd occurrence location, that were employed for building habitat suitability model (Supplementary Material Appendix 1, Table 1)
Summary
As part of the recent "biodiversity crisis," many amphibian populations are declining worldwide (e.g., Blaustein et al 1994; Wake and Vredenburg 2008; Catenazzi 2015; Scheele et al 2019). The recently described chytrid fungus Batrachochytrium dendrobatidis (Longcore et al 1999) is considered the main cause of population declines in different continents, driving species to extinction in Australia, South and Central America (Fisher and Garner 2020; Scheele et al 2019). The global Bd occurrence and its effects on amphibian populations have been recently reviewed and mapped (Olson et al 2013; Lötters et al 2009; Scheele et al 2019). Six different Bd lineages have been identified by multilocus sequence typing, but only the global pandemic lineage (GPL) seems associated to widespread chytridiomycosis outbreaks that caused populations declines (Fisher and Garner 2020). The main factor spreading the pandemic Bd lineage in different parts of the world and in different time periods is the international trade of amphibians and other aquatic animals for food, research, collection or company (Olson et al 2013)
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