Arnold contributes to understanding a worldwide amphibian fungal disease

  • Published
  • By Stevia Morawski, Arnold AFB Ecologist/Biologist
Arnold Air Force Base is taking part in a Department of Defense study to provide research information that could lessen the impact of a world-wide amphibian fungal disease called Chytridiomycosis, or Chytrid. The fungus affects amphibians and causes sporadic death in some species and widespread mortality in others.

Beginning in the 1970s, biologists in Australia noticed unexplained amphibian die-offs and eventually the fungus Chytrid was determined as the culprit. Chytrid is thought to have originated in Asia and spread due to human activity, especially the pet trade.

Chytrid has since been discovered on all continents and is causing one of the largest biodiversity losses in recorded history, already causing the extinction of at least 90 species. A study published in Science Magazine estimates the fungi has caused startling declines in 501 amphibian species worldwide.

In the United States, the first major amphibian die-offs occurred in the 1980s, though infected specimens were found dating back to the 1960s. Surveys have found the fungus in almost every state, and it was found in Tennessee in the early 2000s. The Department of Defense has funded multiple surveys and research projects through its DOD Legacy Program and Strategic Environmental Research and Development Program.

One of those funded SERDP projects chose Arnold AFB as a study site. The study is part of a national collaboration between several universities, and in addition to Arnold AFB, Camp Ethan Allen Training Site, Fort Polk Army Base, and White Sands Missile Range are being surveyed.

Dr. Emily Hall, a postdoctoral researcher at Vanderbilt University School of Medicine’s Rollins-Smith Laboratory, is in her third year of studying this disease at Arnold.

“The fungus was found at all five of our study sites,” said Hall. “It’s everywhere.”

Members of the lab visit five ponds across Arnold three to four times per season and catch everything they encounter for one hour.

“Usually we turn logs to catch salamanders and use nets for frogs,” Hall said.

Size measurements are taken for all animals that are caught, and their skin is swabbed with cotton, which collects the DNA of the fungus. All animals are released after they are caught. Later, the DNA is run in the lab so researchers can quantify how much Chytrid is present on their skin.

“Arnold has an amazing diversity of amphibians with 14 species of frogs and toads and 12 species of salamanders,” said John Lamb, an AEDC biologist who is helping facilitate the study on the base.

Out of the 23 species found in surveys, Chytrid fungus was found on 17 species in varying amounts.

Though amphibians are an often overlooked animal group, their importance should not be underestimated.

“They are a keystone part of ecosystems, making up a large part of the biomass, food for other animals, and they are a transfer link between aquatic and terrestrial nutrient flow,” Hall said, “and they eat pests!”

Lamb also emphasized the importance of amphibians in aquatic and terrestrial ecosystems and their inherent cultural value.

“Our frogs and toads create a beautiful soundscape at night, each species having its own unique breeding call,” he said.

Though disease caused by Chytrid fungus is a worldwide problem, there is much to be done to understand the impacts at a local scale. At the end of the five-year study, the data collected will be analyzed with epidemiology models to test different mitigation strategies for the disease.

One mitigation strategy includes habitat modification, where the water level in each pond is lowered or raised. However, Hall says, “It’s important to understand if you can manage for Chytrid in the first place.”

The study also seeks to understand the ways in which climate change complicates the trajectory of the disease. Tennessee has been experiencing more extreme variations in temperature and rainfall, which is projected to worsen as climate change progresses. This will cause mounting environmental pressure on amphibian populations and their immune development, while the disease that plagues them will be much less affected.

“The fungus can adjust much quicker (to climate change) because its generation time is days,” Hall said. “Frogs and salamanders have years between generations. So adapting to those kinds of changes is going to be troublesome.”

While mitigation strategies are being evaluated, researchers take precautions so that they do not contribute to the spread of the disease. Amphibians are handled with disposable gloves and sterile equipment. Between research sites, equipment and footwear are cleaned and dried. Amphibians are not moved from one site to another.

“Different strains vary in how lethal they are,” Hall said. “If you want to protect your species diversity, you need to stop disease introduction.”