Evaluating the Prevalence of the Amphibian Chytrid Fungus, Batrachochytrium dendrobatidis, in the Southeastern U.S.: Any Evidence of Disease-Related Population Declines?

Science Center Objects

Pathogens and infectious disease play a role in some recent species extinctions and are likely to impact biodiversity in the future. Environmental DNA - eDNA - is coupled with traditional amphibian sampling methods to determine the distribution and prevalence of the amphibian chytrid fungus, also known as Bd, in the southeastern US. 

Evaluating the Prevalence of the Amphibian Chytrid Fungus, Batrachochytrium dendrobatidis, in the Southeastern U.S.: Any Evidenc

Environmental DNA - eDNA - can be used with traditional sampling methods to determine the distribution/prevalence of pathogens. 

PROJECT COMPLETED

The Science Issue and Relevance: Pathogens and infectious diseases are of significant concern in biological conservation because of increasing evidence that they have played a role in some recent species extinctions, and are likely to impact biological diversity in the future as well. Pathogens can impede the recovery of rare species and may be one of the biggest threats to species that are already endangered, especially when disease acts in concert with other drivers of extinction such as habitat loss and alteration. Population declines and extinctions of at least 200 species of amphibians worldwide have been attributed to the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis. Although this pathogen can be widespread in some regions, it does not necessarily culminate in disease outbreaks and subsequent catastrophic die-offs, population declines and extinctions in all geographic areas (e.g. the southeastern USA).

We collaborated with USGS hydrologists to employ a relatively new technique to sample water inhabited by amphibians for the presence of Bd (referred to as “environmental DNA), coupled with traditional methods for sampling live amphibians for Bd. This two-pronged approach provides a stronger, more comprehensive assay for the potential exposure of amphibians to Bd. Our results indicate that a lack of detection of Bd on amphibians does not imply an absence of this pathogen in the environment. Discordance between water and biological samples underscores the need to conduct both environmental and biological sampling to elucidate the distribution of this pathogen in the environment and its potential to infect amphibians. Contrary to the pattern of declines and extinctions observed in Mesoamerica and Australia, Bd is quite ubiquitous in the southeastern US without noticeable changes to amphibian populations. However, mortality events associated with other known amphibian pathogens (e.g. ranavirus and the perkinsus like organism) were observed during the course of this study and are causes for concern, as global climate change, habitat loss and other stressors can interact with agents of disease to induce, or even amplify, their effects on amphibian populations.

Evaluating the Prevalence of the Amphibian Chytrid Fungus, Batrachochytrium dendrobatidis, in the Southeastern U.S.: Any Evidenc

USGS researchers detected Bd in every state sampled and in seven of the nine US Department of Interior lands sampled. 

Methodology for Addressing the Issue: We sampled more than 1,500 amphibians and water from a variety of wetlands, streams, and caves from 71 sites that represent nine national parks and wildlife refuges extending from the (Southern) Appalachian Mountains to the Florida Keys. A total of 40 different species of amphibians (20 species each for salamanders and anurans) were sampled. To date, our sampling represents the most comprehensive effort to determine the distribution and prevalence of this pathogen in the southeastern U.S. We have detected Bd in each state and in seven of nine US Department of Interior lands sampled. In most cases these were the first records of Bd on the properties sampled and are only the second and third records for Florida and Alabama, respectively.

Future Steps: None planned. Project finished and presently preparing a manuscript.