Why Does Amphibian Chytrid (Batrachochytrium dendrobatidis) Not Occur Everywhere? An Exploratory Study in Missouri Ponds

Abstract

The amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), is a globally emerging pathogen that has caused widespread amphibian population declines, extirpations, and extinctions. However, Bd does not occur in all apparently suitable amphibian populations, even within regions where it is widespread, and it is often unclear why Bd occurs in some habitats but not others. In this study, we rigorously surveyed the amphibian and invertebrate biodiversity of 29 ponds in Missouri, screened resident amphibian larvae (Rana (Lithobates) sp.) for Bd infection, and characterized the aquatic physiochemical environment of each pond (temperature pH, conductivity, nitrogen, phosphorus, and chlorophyll-a). Our goal was to generate hypotheses toward answering the question, “Why does Bd not occur in all apparently suitable habitats?” Bd occurred in assayed amphibians in 11 of the 29 ponds in our study area (38% of ponds). We found no significant relationship between any single biotic or abiotic variable and presence of Bd. However, multivariate analyses (nonmetric multidimensional scaling and permutational tests of dispersion) revealed that ponds in which Bd occurred were a restricted subset of all ponds in terms of amphibian community structure, macroinvertebrate community structure, and pond physiochemistry. In other words, Bd ponds from 6 different conservation areas were more similar to each other than would be expected based on chance. The results of a structural equation model suggest that patterns in the occurrence of Bd among ponds are primarily attributable to variation in macroinvertebrate community structure. When combined with recent results showing that Bd can infect invertebrates as well as amphibians, we suggest that additional research should focus on the role played by non-amphibian biota in determining the presence, prevalence, and pathogenicity of Bd in amphibian populations.

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

“…). If abiotic or biotic factors such as temperature, stream flow, water chemistry, and/or zoospore consumption by aquatic organisms are able to substantially increase zoospore death rate beyond the values seen in the lab (Tunstall ; Strauss & Smith ; Venesky et al . ; Heard et al .…”

Amphibian Alliance for Zero Extinction Sites in Chiapas and Oaxaca

“…Strauss and Smith (2013) have shown that the composition of zooplankton in ponds without Bd are more alike than expected by chance and that they differ in this respect from otherwise similar ponds testing positive for Bd. Thus, by extension, a population of susceptible amphibians might be spared given the right combination of zooplankton at a localized scale.…”

“…Increasingly, however, there is evidence of populations of highly susceptible species that are now increasing in size and/or expanding in range (Tobler et al 2012;Newell et al 2013;Scheele et al 2014). Coupled with these encouraging findings is the recognition that while Bd becomes ubiquitous when it enters a region for the first time, some areas where it has existed for long periods show seemingly inexplicable gaps in presence (Strauss & Smith 2013).…”

“…• A combination of subtle environmental variables - Strauss and Smith (2013) put forward this idea to explain the presence or absence of Bd in ponds in Missouri, USA, but found little support for it.…”

Disease dynamics of red-spotted newts and their anuran prey in a montane pond community

“…One species that may serve as a reservoir for both Bd and Rv is the eastern newt Notophthalmus viridescens (Raffel et al 2010, Strauss & Smith 2013. This species is long-lived and exhibits variable life histories throughout its range (Petranka 1998).…”