Oregon State researchers say Daphnia magna may be able to control chytrid fungus levels
By Bob Berwyn
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SUMMIT COUNTY — Working in a laboratory setting, Oregon State researchers say they’ve discovered a freshwater organism that eats the free-swimming spores of a fungal pathogen that’s been devastating amphibian populations worldwide, including Colorado’s endangered boreal toad.
This tiny zooplankton, called Daphnia magna, could provide a desperately needed tool for biological control of this deadly fungus if field studies show that the same process works in a natural setting.
The research was was supported by the National Science Foundation and reported this week in the journal Biodiversity and Conservation. Co-authors and researchers included Lisa Truong and Andrew R. Blaustein.
“These are just your average Daphnia,” zoologist and lead author Julia Buck said Friday in a telephone interview before heading into the field for more research. The small organisms are sometimes described as aquatic fleas. They’re native northern and western North America and have been used for decades to test water for toxins.
“They’re filter feeders … so they’re just taking in these zoospores,” she said.
“There was evidence that zooplankton would eat some other types of fungi, so we wanted to find out if Daphnia would consume the chytrid fungus,” said Buck, an OSU doctoral student in zoology and lead author on the study. “Our laboratory experiments and DNA analysis confirmed that it would eat the zoospore, the free-swimming stage of the fungus.”
Buck said it’s going to take extensive field studies to determine if using the Daphnia will work as a biological control agent for the chytrid fungus.
“Certainly, we hope this information could be used to control it,” she said.
The fungus, B. dendrobatidis, is referred to as a “chytrid” fungus. When concentrations are high enough, the fungus infects amphibian hosts and can kill them by disrupting their electrolyte balance, leading to death from cardiac arrest
One researcher has called its impact on amphibians “the most spectacular loss of vertebrate biodiversity due to disease in recorded history.”
“We feel that biological control offers the best chance to control this fungal disease, and now we have a good candidate for that,” she said. “Efforts to eradicate this disease have been unsuccessful, but so far no one has attempted biocontrol of the chytrid fungus. That may be the way to go.”
The chytrid fungus, which was only identified in 1998, is not always deadly at low levels of infestation, Buck said. It may not be necessary to completely eliminate it, but rather just reduce its density in order to prevent mortality. Biological controls can work well in that type of situation.
Amphibians have been one of the great survival stories in Earth’s history, evolving about 400 million years ago and surviving to the present while many other life forms came and went, including the dinosaurs. But in recent decades the global decline of amphibians has reached crisis proportions, almost certainly from multiple causes that include habitat destruction, pollution, increases in ultraviolet light due to ozone depletion, invasive species and other issues.
High on the list, however, is the chytrid fungus that has been documented to be destroying amphibians around the world, through a disease called chytridiomycosis.
Its impact has been severe and defied various attempts to control it, even including use of fungicides on individual amphibians. Chytridiomycosis has been responsible for “unprecedented population declines and extinctions globally,” the researchers said in their report.
“About one third of the amphibians in the world are now threatened and many have gone extinct,” said Andrew Blaustein, a professor of zoology, co-author on this study and an international leader in the study of amphibian decline.
“It’s clear there are multiple threats to amphibians, but disease seems to be a dominant cause,” he said.
Although they have survived for hundreds of millions of years, amphibians may be especially vulnerable to rapid environmental changes and new challenges that are both natural and human-caused. They have a permeable skin, and exposure to both terrestrial and aquatic environments.
Because of this, OSU researchers said, other animals such as mammals, birds and fish have so far not experienced such dramatic population declines.