The two chytrid pathogens of amphibians in Eurasia—climatic niches and future expansion

Abstract

Background Climate affects the thermal adaptation and distribution of hosts, and drives the spread of Chytridiomycosis—a keratin-associated infectious disease of amphibians caused by the sister pathogens Batrachochytrium dendrobatidi (Bd) and B. salamandrivorans (Bsal). We focus on their climate-pathogen relationships in Eurasia, the only region where their geographical distributions overlap. Eurasia harbours invaded and native areas of both pathogens and the natural habitats where they co-exist, making it an ideal region to examine their environmental niche correlations. Our understanding of how climate change will affect their distribution is broadened by the differences in climate correlates and niche characteristics between Bd and Bsal in Asia and Europe. This knowledge has potential conservation implications, informing future spread of the disease in different regions. Results We quantified the environmental niche overlap between Bd and Bsal in Eurasia using niche analyses. Results revealed partial overlap in the niche with a unique 4% of non-overlapping values for Bsal, suggesting segregation along certain climate axes. Bd tolerates higher temperature fluctuations, while Bsal requires more stable, lower temperature and wetter conditions. Projections of their Realized Climatic Niches (RCNs) to future conditions show a larger expansion of suitable ranges (SRs) for Bd compared to Bsal in both Asia and Europe, with their centroids shifting in different directions. Notably, both pathogens' highly suitable areas in Asia are expected to shrink significantly, especially under the extreme climate scenarios. In Europe, they are expected to expand significantly. Conclusions Climate change will impact or increase disease risk to amphibian hosts, particularly in Europe. Given the shared niche space of the two pathogens across available climate gradients, as has already been witnessed in Eurasia with an increased range expansion and niche overlap due to climate change, we expect that regions where Bsal is currently absent but salamanders are present, and where Bd is already prevalent, may be conducive for the spread of Bsal.

Alpine salamanders at risk? The current status of an emerging fungal pathogen

“…Moreover, Bsal suitability, as shown by three thresholds of our SDM, underlines our call for pre-invasion measures as it overlaps with our sampling sites, the distribution of Alpine salamanders and other syntopic Bsal hosts (Fig 1). However, our predictions are slightly different to those from [47] which show solely suitability along the edges of the alpine region but not in the centre. This may be due to methodological differences as we used an extended dataset of Bsal-records and a finer resolution [10,47].…”

“…However, our predictions are slightly different to those from [47] which show solely suitability along the edges of the alpine region but not in the centre. This may be due to methodological differences as we used an extended dataset of Bsal-records and a finer resolution [10,47]. Still our model likely underestimates the habitat suitability for the pathogen, as Bsal is continuously spreading and is not in equilibrium with the environment in its invasive range […”

Ecological Barriers for an Amphibian Pathogen: A Narrow Ecological Niche for Batrachochytrium salamandrivorans in an Asian Chytrid Hotspot

“…Finally, our study suggests a complex interplay of ecological and biological factors in dictating the distribution of amphibian chytrid fungal pathogens. As climate change continues to alter key ecological factors, the risk of Bsal is expected to persist in coastal areas and higher elevations, even though habitats with medium-to-high climatic suitability for Bsal are likely to decrease [ 37 , 84 ]. The international and regional trade in amphibians has been identified as a significant driver for the translocation of both Bd and Bsal pathogens [ 5 , 29 ].…”

“…In addition, in terms of the niche space and geographic distribution of Bsal , ecological niche models can be useful in predicting the potential suitable habitats of pathogens and evaluating the different influences of variables on pathogen occurrences [ 36 ]. Prior work has predicted the potential distribution of Bsal in Asia, with diurnal temperature range identified as the most important factor [ 15 , 37 ], but they failed to consider biotic interactions that might alter the range estimate. For example, alterations in biodiversity significantly impact pathogen dynamics through mechanisms such as dilution and amplification effects [ 38 , 39 ].…”

Impact of Climate Change on the Distribution of Three Rare Salamanders (Liua shihi, Pseudohynobius jinfo, and Tylototriton wenxianensis) in Chongqing, China, and Their Conservation Implications

“…Habitat loss represents the most prevalent threat to amphibian species, leading to the destruction or fragmentation of the environments upon which these species depend for their survival [ 16 ]. Pathogenic diseases such as the lethal chytrid fungi Batrachochytrium dendrobatidis ( Bd ) and Batrachochytrium salamandrivorans ( Bsal ) [ 17 , 18 ], exacerbated by climate change and habitat alteration, are responsible for rapid and widespread declines in amphibian populations, often driving species to the brink of extinction. The spread of pathogens such as the chytrid fungus has been linked to global amphibian declines, facilitated by environmental changes and human movement [ 19 , 20 , 21 ].…”