Introduction
Amphibians worldwide face considerable threats, including habitat loss, climate change, and disease, which contribute to severe population declines and biodiversity loss (Amphibiaweb, 2023). Chytridiomycosis, a disease caused by the chytrid fungi Batrachochytrium dendrobatidis (Bd ) and B. salamandrivorans (Bsal ), is a major driver of these declines (Longcore et al., 1999; Martel et al., 2013; Scheele et al., 2019). Both Bd and Bsal are thought to have originated in Asia, with Bd portraying multiple lineages in the region (Martel et al., 2014; O’hanlon et al., 2018).Bd affects all three amphibian orders and has caused widespread declines, particularly in anuran species across all amphibian-inhabited continents (Scheele et al., 2019). In contrast, although present in Asia, Bsal has led to severe declines of native salamanders only in Europe so far (Fisher & Garner, 2020), however, the impending threat for the highly diverse Northern American and Neotropical urodelans is significant (Carter et al., 2020; Crawshaw et al., 2022; García-Rodríguez et al., 2022; Moubarak et al., 2022; North AmericanBsal Task Force, 2022; Yap et al., 2015).
Although Bsal primarily infects urodelans, recent studies show that anurans can act as reservoir hosts or as transmitters (Lötters et al., 2020; Nguyen et al., 2017; Schulz et al., 2020; Stegen et al., 2017; Towe et al., 2021). This role increases disease risk to sensitive salamander species and populations. Therefore, identifying reservoir hosts is crucial for understanding infection dynamics and potential occurrences as Bsal continues to expand its range and threaten biodiversity (Martel et al., 2020; Spitzen-Van Der Sluijs et al., 2016).
Bsal has restricted distributional areas, co-occurring withBd in several microhabitats (Laking et al., 2017; Lötters et al., 2020). Bd -Bsal occurrences can potentially generate new genotypes with heightened pathogenicity (Farrer et al., 2011; Fisher & Garner, 2020; Wacker et al., 2023). Bsal has stronger pathogenicity compared to Bd within a shared host species, leading to more severe infection outcomes (Farrer et al., 2017). Out of documented 67 susceptible host species for Bsal , nearly 32 species also can be infected by Bd (Castro Monzon et al., 2023; Olson et al., 2021), these shared species could serve as the hyper-reservoirs or gain greater impacts from both pathogens. Importantly, Bd -Bsal coinfections have been reported in three urodelean species in natural habitats (Lötters et al., 2020; Lötters et al., 2018), and such coinfections are known to increase infection severity and disease risk under the laboratory experimental conditions (Longo et al., 2019; Ribas et al., 2022). These emphasize the importance of Bsal screening in natural habitats where Bdoccurs.
In Southeast Asia (Vietnam), Bsal co-occurs together with the globalized genotype Bd GPL (Laking et al., 2017). However, knowledge on Bsal infection is scarce in other Asian amphibian hotspots where different Bd lineages are found. South China, for example, harbors the unique Asian genotype Bd Asia3 alongsideBd GPL (Byrne et al., 2019).
Here, we hypothesize that Bsal co-occurs together with Bdpopulations in South China. To investigate this, we screened forBsal in salamanders and potential anuran reservoir hosts within regional amphibian hotspot in South China, which is recognized for its diverse Bd genotypes spanning various natural habitats. We also assessed the influence of climatic factors on Bsal distribution by estimating its potential range under the current climatic conditions. Analyzing the presence of Bsal in areas with high Bddiversity will enhance our comprehension of Bsal niche dynamics and pathogenicity. This has significant implications for amphibian conservation in the context of pathogen virulence evolution.