Effects of host species and environmental factors on the prevalence of Batrachochytrium dendrobatidis in northern Europe

Abstract

The fungal pathogen Batrachochytrium dendrobatidis (Bd) poses a major threat to amphibian populations. To assist efforts to address such threats, we examined differences in Bd host infection prevalence among amphibian species and its relations to both local environmental factors in breeding habitats and landscape variables measured at three scales (500, 2000 and 5000 m radii) around breeding sites in southernmost Sweden. We sampled 947 anurans of six species in 31 ponds and assessed their infection status. We then examined correlations of infection prevalence with canopy cover, pond perimeter and pH (treated as local-scale pond characteristics), and the number of ponds, area of arable land, area of mature forest, number of resident people and presence of sea within the three radii (treated as landscape variables). The Bd infection prevalence was very low, 0.5–1.0%, in two of the six anuran species (Bufo bufo and Rana temporaria), and substantially higher (13–64%) in the other four (Bombina bombina, Bufotes variabilis, Epidalea calamita, Rana arvalis). In the latter four species Bd infection prevalence was positively associated with ponds’ pH (site range: 5.3–8.1), and negatively associated with areas of mature forest and/or wetlands in the surroundings. Our results show that the infection dynamics of Bd are complex and associated with host species, local pond characteristics and several landscape variables at larger spatial scales. Knowledge of environmental factors associated with Bd infections and differences in species’ susceptibility may help to counter further spread of the disease and guide conservation action plans, especially for the most threatened species.

Spatiotemporal heterogeneity decouples infection parameters of amphibian chytridiomycosis

“…If river densities are low, Bd mean intensity increases slightly when precipitation levels are low with our observations of higher prevalence in populations expe- (Kriger, Pereoglou, & Hero, 2007;Ron, 2005), and field studies indicating that Bd outbreaks might be more likely under wet conditions (Bosch et al, 2007;Lips et al, 2006). Yet, no published study has linked infection intensity with a reduction in either (a) the size of water basin (hydroshed area) or (b) the density of river networks (however, see Kärvemo et al, 2018;Spitzen-van der Sluijs, Canessa, Martel, & Pasmans, 2017). We found that as hydroshed area increased, infection intensity decreased slightly, suggesting that R. pipiens populations concentrated within a small drainage basin may facilitate the proliferation and transmission of zoospores, as increasing host population density increases transmission rates (Briggs et al, 2010).…”

“…infectivity and virulence; O'Hanlon et al, 2018), and the surrounding abiotic and biotic environment (e.g. environmental heterogeneity and landscape structure; Kärvemo, Meurling, Berger, Höglung, & Laurila, 2018).…”

Thermal Performance Curves of Multiple Isolates of Batrachochytrium dendrobatidis, a Lethal Pathogen of Amphibians

“…Chytridiomycosis is a disease that has impacted amphibians in a wide range of environmental conditions (21,60). Past studies have attempted to link Bd phenotypic patterns with environmental factors in order to understand how abiotic factors might mitigate or exacerbate disease (5,30,43,61). For example, both Becker et al (30) and Greener et al (21) documented considerable phenotypic variation for isolates within the BdGPL that was associated with differential pathogenicity in common susceptible host species (Lithobates sylvaticus and Alytes obstetricans, respectively).…”

The first detection of the fungal pathogen batrachochytrium dendrobatidis in Norway with no evidence of population declines for great crested and smooth newts based on modeling on traditional trapping data

“…The Bd‐positive ponds are all located within one region of our study area, although they are dispersed in the landscape in‐between Bd‐negative ponds. We cannot exclude the presence of false negatives in our data (Erickson et al., 2019) as eDNA is known to show “patchy distributions” within environments, but a similar distribution pattern has also been found in other countries, such as Sweden (Kärvemo et al., 2018) and the UK (Smith, 2014), that both have hosted Bd for a longer time. Also, in Sweden, the number of ponds with Bd is increasing in line with increasing monitoring time, suggesting that a larger Norwegian sample size and/or sampling at more optimal sampling times would result in a higher number of positive ponds in the Bd‐positive area (Kärvemo et al., 2018).…”