Species distribution models predict the geographic expansion of an enzootic amphibian pathogen

Abstract

Globally, numerous amphibian species have declined due to the introduction of the chytrid fungus Batrachochytrium dendrobatidis (Bd). However, the understanding of the spatiotemporal dynamics remains incomplete. Therefore, estimating the current geographic distribution of Bd is urgently needed, especially in countries like Costa Rica, where susceptible species are still recovering from Bd‐driven declines. We conducted model tuning and spatial analysis to compare the habitat suitability for epizootic and enzootic Bd in Costa Rica and to identify data‐deficient regions, opportunistic sampling, and Bd hotspots. Our dataset combined two methods of detection (histology and PCR methods) for a total of 451 Bd‐positive records from 34 localities. We found that the distribution of enzootic Bd in Costa Rica increased 60% since previous estimates in the early 2000s and extended to highlands and dry lowlands that were considered unsuitable for Bd. We also found that Bd is common across protected lands (80%) and within the herpetological provinces containing the highest amphibian richness and endemism in Costa Rica. Opportunistic sampling of Bd has focused on sites where epizootics occurred with the strongest intensity, leading to deficient or absent sampling across the Talamanca Range, the Nicoya Peninsula, and the northern lowlands. Our results showed that PCR increased the power of Bd detection in lowlands and favored the identification of Bd hotspots across the Caribbean side of Costa Rica. Our results add to the understanding of disease spread during enzootics and can be used to identify new hotspots for disease to mitigate future outbreaks of this pathogen. Abstract in Spanish is available with online material

Anticipating the potential impacts of Batrachochytrium salamandrivorans on Neotropical salamander diversity

“…The potential distribution for Bsal also corresponds with some areas of the predicted distribution of Bd at both the regional level (Ron, 2005) and the country level in Mexico (Bolom‐Huet et al, 2019) and Costa Rica (Zumbado‐Ulate et al, 2020). Many amphibian species within these countries have suffered catastrophic declines associated with Bd infection (Cheng et al, 2011; Lips, 1998; Zumbado‐Ulate et al, 2019), yet Bd suitability models were not generated until several decades after the introduction of the pathogen.…”

Bioclimatic and anthropogenic variables shape the occurrence of Batrachochytrium dendrobatidis over a large latitudinal gradient

“…Elevated risk of Bd infection in areas close to human activities and settlements has been described previously in both temperate and tropical regions 23 , 25 , 36 , 43 , 75 , 82 . Most studies based species distribution models of Bd in the Americas have found an association of Bd occurrence with several climatic variables, notably precipitation, temperature and seasonality 13 , 21 , 32 , 33 , 44 , although few incorporate explicitly the effect of human impact, such as urban centres, in the analyses 43 . Interestingly, Zumbado-Ulate et al 33 found a higher Bd occurrence in undisturbed ecosystems or protected areas, highlighting the fact that Bd occurrence is context specific as can be influenced by many factors including time of Bd introduction, species and population susceptibility, among others.…”

“…An alternative hypothesis is that instead of high-risk areas we might be capturing oversampled regions 86 . Therefore, we recommend considering other methods such as species distribution models 43 or kriging interpolation 33 to have a more accurate picture of the identified high-risk areas.…”

“…However, many aspects of the landscape epidemiology of Bd (i.e., studies comprising different ecoregions) remain unknown. These include pathogen distribution in under-surveyed areas (e.g., parts of Africa and South America), mechanisms for local or regional spread and identification of reservoir hosts (amphibian and non-amphibian) 8 , 14 , 31 – 33 . These can be relevant for Bd mitigation, for example helping to predict the potential impacts of chytridiomycosis in understudied areas or following Bd introduction into naïve amphibian populations.…”

Assessing Suitable Habitats for Treefrog Species after Previous Declines in Costa Rica

“…This mountain habitat, well-suited for the growth and proliferation of Bd [15], was home to many treefrog species, particularly those in the genera Isthmohyla, Duellmanohyla, and Agalychnis [26]. Although Bd is now endemic across Mesoamerica [27][28][29][30][31] and numerous species have shown resilience [32], many areas and amphibian species have failed to recover after the introduction of Bd [26]. Other amphibian species appear to have spread during epizootics and enzootics phases of Bd, potentially serving as a reservoir for the pathogen [33].…”