daphnia magna (credit: Photo courtesy of Oregon State University)
Researchers at Oregon State University may have made a breakthrough in the current battle against a fungus that is devastating amphibians across the world. It appears that a species of daphnia will feed on the spores of the fungus offering hope of a realistic biological control in the wild.
Fungus devastating amphibian populations.
Batrachochytrium dendrobatidis is a chytrid fungus that was first discovered in 1998. Since it’s discovery it has swept around the world and devastated many amphibian populations including frogs. The way it is distributed across habitats or why it is so devastating is not fully understood. There does seem to be some evidence that populations exposed to cabaryl pesticides are more susceptible to the impacts of the fungus.
Zoologists across the world have been trying to find a way of tackling the epidemic. Using fungicides and bacteria to fight the fungus have worked in the lab but trying to get the system to work effectively in the field is much more difficult.
Zooplankton feeds on the spores of the fungus.
The latest work by zoologists at Oregon State University has discovered the the zooplankton Daphina magna will feed on the B. dendrobatidis fungus while the fungus is in the free swimming stage of a zoospore. This offers a realistic hope of a control method if seeding infected sites in the wild with D. magna proves beneficial.
Low levels of B. dendrobatidis does not appear to be fatal to amphibians so if the concentrations of the fungus can be controlled through predation then the risk of infection can be reduced.
“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 Julia 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 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.“
Fungus causes chytridiomycosis.
In amphibians the zoospores of B. dendrobatidis are at their most infective when the spores are between 3–5 ?m in diameter. The way of infection could be through the permeable skin of the amphibian rather than through ingestion. The infection leads to the disease called chytridiomycosis. This disease seems to change the electrolyte levels in amphibians and kills them through cardiac arrest.
“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.
The Big Swab UK.
In the UK it is known from a 2008 survey that chytridiomycosis is widespread throughout the country and it affects all our native species of amphibians. The Zoological Society of London is working with the Department of Environment, Farming and Rural Affairs (DEFRA) and volunteers from many of the amphibian and reptile groups to get a bigger picture of the current effects of the disease.
The Big Swab as it is commonly known took place during the Spring and Summer of 2011. It revisited the sampling sites of the original 2008 survey to survey the current state. Some additional sites of breeding populations of newts have also been added to the sampling sites where there was limited data available in the first survey.
External sites:
Predation by zooplankton on Batrachochytrium dendrobatidis: biological control of the deadly amphibian chytrid fungus?
The 2011 UK Chytrid Survey by ZSL.
The Big Swab.
