Tracking Deadly Fungus

USF researchers have found that a deadly amphibian pathogen can also infect crayfish.

 

USF biologist Jason Rohr works in the field.

 

By Vickie Chachere

USF News

 

TAMPA, Fla. (Dec. 18, 2012) – New research from University of South Florida biologists has found the deadly chytrid fungus, which is implicated in the decline of frog populations worldwide and was thought to only infect amphibians, can also infect crayfish.

 

The research from USF biologists Taegan McMahon and Jason Rohr was published Monday in the Proceedings of the National Academies of Sciences.

 

In collaboration with the laboratories of Pieter Johnson and Valerie McKenzie at the University of Colorado and the laboratory of Corrine Richards-Zawacki at the University of Tulane, the authors collected crayfish and amphibians from Colorado and Louisiana and screened them for the presence of the fungus (Batrachochytrium dendrobatidis) using light microscopy, histology, and DNA testing. They discovered that fungal prevalence in the crayfish was up to 29 percent and that crayfish presence was a positive predictor of chytrid infections in co-occurring amphibians.

 

”We also exposed uninfected mosquito fish and crayfish to water containing the fungus,” McMahon said.  “The mosquito fish did not get infected, but 91 percent of the crayfish were positive for the fungus seven weeks after the initial exposure.”

 

The scientists grew the chytrid fungus on crayfish exoskeletons and gastrointestinal tracts under sterile laboratory conditions and then tested whether the crayfish might be suitable hosts for the fungus, McMahon said. The fungus embedded in the crayfish gastrointestinal tracts was associated with both reduced growth rates and elevated mortality.

 

“Fungal-contaminated water that had been filtered to remove the fungus caused crayfish mortality and gill damage”, proclaimed Rohr.  “This provided evidence that the chytrid fungus releases a chemical factor that can cause pathology even in the absence of infection.”

 

Interestingly, some crayfish cleared their chytrid infections in the laboratory whereas others maintained their infections for 12 weeks. 

 

“The most important discovery was a 70 percent transmission rate of the fungus from crayfish to tadpoles,” Rohr stated.  “This provided evidence that crayfish can be a source of infection for declining amphibians.”

 

McMahon and Rohr suggest that these findings might help explain how the fungus can persist in the environment in the absence of amphibian hosts, how it can be so deadly to amphibians without causing its own demise (because it can survive in other hosts), and why there appears to be such a patchy fungal distribution and such variable rates of fungal spread (because the distribution and spread might be partly a function of other host taxa).

 

“We are particularly excited by these findings because managing non-amphibian hosts for the chytrid fungus and identifying the fungal chemical that can cause pathology in the absence of infection might provide new hope for imperiled amphibians,” McMahon concluded.

 

The full text of the paper by McMahon, a PhD candidate, and Rohr, an Associate Professor of Biology, can be read here.

 

Vickie Chachere can be reached at 813-974-6251.