Wetland characteristics influence disease risk for a threatened amphibian

Abstract

Identifying determinants of the probability and intensity of infections is important for understanding the epidemiology of wildlife diseases, and for managing their impact on threatened species. Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis, has decimated populations of some amphibians. However, recent studies have identified important environmental constraints on the disease, related to the pathogen's physiological tolerances. In this study, we identified several intrinsic and extrinsic determinants of the probability and intensity of chytrid infections for the threatened growling grass frog (Litoria raniformis) in southeastern Australia, and used mark-recapture to estimate the effect of chytrid infections on the probability of survival of these frogs. Water temperature and salinity had negative effects on both the probability and intensity of chytrid infections. We coupled models of the infection process with a model of the effect of chytrid infections on the probability of survival to assess variation in the impact of chytridiomycosis between wetlands with differing temperature and salinity profiles. Our results suggest that warm, saline wetlands may be refuges from chytridiomycosis for L. raniformis, and should be priorities for protection. Our results also suggest that management actions that increase water temperature (e.g., reducing canopy shading) and salinity (e.g., complementing inflows with groundwater) could be trialed to reduce the impacts of chytridiomycosis on this species. This and other recent studies highlight the value of research on environmental risk factors for chytridiomycosis.

Elevated salinity blocks pathogen transmission and improves host survival from the global amphibian chytrid pandemic: Implications for translocations

“…Few studies have dealt with the manipulation of environmental salinity as a management approach for mitigating Bd load and impact in habitats, although it has been suggested (Scheele, Hunter, et al., ; Stockwell, Clulow, et al., ; Stockwell et al., ; Stockwell, Storrie, et al, 2015). The susceptibility of Bd to increasing salinity has been demonstrated in culture through reduced growth rates and motility/viability (Johnson et al., ; Stockwell et al., ) and there is evidence in support of benefits of salinity to frogs and tadpoles in some studies (Heard et al., ; Stockwell, Clulow, et al., ; Stockwell et al., ; Stockwell, Storrie, et al, 2015) in addition to the current study. It is worth noting that there are probably scenarios where manipulating salinity on a scale that would be detectable in systems where salinity is naturally low could be difficult.…”

“…It is worth noting that attempts to manipulate water temperature in this study did not produce a large enough thermal shift to directly confirm this as an experimental treatment, despite attempts by several methods that might have been able to be applied in a field setting. This is important because active and passive strategies have been proposed in the literature to raise air and water temperatures, such as using dark substrates in ponds and removal of aquatic and overhanging terrestrial vegetation to reduce shading and increase exposure to solar radiance (Becker, Rodriguez, Longo, Talaba, & Zamudio, ; Becker & Zamudio, ; Heard et al., ; Raffel, Michel, Sites, & Rohr, ; Scheele, Hunter, et al., ). Our experience suggests that directly managing temperature in external water bodies by passive or active management of temperature will be a challenging environmental management strategy to implement, even if a potentially important one (Scheele, Hunter, et al., ).…”

Resistance, tolerance and environmental transmission dynamics determine host extinction risk in a load‐dependent amphibian disease

“…; Heard et al . ; Schmeller et al . ), then we might expect a reduction, though not an elimination, of Bd invasion probability and amphibian extinction risk.…”

Canopy cover and drought influence the landscape epidemiology of an amphibian chytrid fungus

“…Instead, we found the effect of canopy cover on Bd prevalence is complex and contingent on weather conditions. Other studies examining the influence of temperature profiles on Bd infections have recommended the clearing of canopy to raise the temperature of wetlands in an effort to reduce the impacts of Bd on amphibian populations (Woodhams et al 2011, Heard et al 2014. Based on our results, such a manipulation could be effective only for particular species under certain weather conditions.…”