Frogs were an important focus for the Alps Bioscan survey in Victoria's Alpine National Park in November last year. The deadly amphibian chytrid fungus, Batrachochytrium dendrobatidis, thrives in cool environments, meaning high-altitude frog populations are particularly susceptible.
Dr Katie Smith, Collection Manager of Vertebrates, led the frog-hunting team at the Alps and explained why this fungus is so insidious. "It's a major contributor to global amphibian decline. Lots of frogs worldwide are affected," she said. "It penetrates their skin and leads to death in some species and individuals, while some are able to survive it and act as carriers."
View this video with a transcript
The museum's frog team searched for frogs in several sites in the Alps and collected skin swabs from every frog found. The swabs will be tested for the presence of chytrid (pronounced 'kit-trid') as part of ongoing monitoring by researchers from the Arthur Rylah Institute for Environmental Research. "We need to know what populations have it and whether this leads to changes in those populations, such as whether there's lower species diversity in areas where chytrid fungus is present."
The chytrid fungus has a free-living stage called a zoospore and a reproductive stage called a zoosporangium. Zoospores can live several weeks in the water until they find a host frog to infect. Once settled, the zoosporangia cause the frog's skin to thicken and slough away. There are a few hypotheses as to how the chytrid fungus kills frogs. One hypothesis proposes that a frog with a heavy chytrid infestation can't maintain its salt balance. Sodium and potassium levels, essential for normal muscle and nerve function, drop significantly and the frog dies from cardiac arrest.
A froglet found during the Alps Bioscan. Froglet species seem to have some resistance to chytrid fungus, and may act as carriers between water bodies.
Image: David Paul
Source: Museum Victoria
Researchers believe that the fungus arrived in Australia in the 1970s, and is linked to the sudden decline (and in some cases, extinction,) of several local species, including the Southern Gastric Brooding Frog and the Southern Corroborree Frog. There are a few theories about how it got here, but the most likely culprit is the international trade in African Clawed Frogs for use in pregnancy tests. In the 1930s it was discovered that injecting one of these frogs with the urine of a pregnant woman caused the animal to produce eggs. Hundreds of thousands of frogs were brought into Australia from Africa for this purpose and probably, with them, the chytrid fungus. While the fungus was first identified in 1998, retrospective examination of historical specimens found the earliest known chytrid infestation on an animal collected in 1938. This African Clawed Frog specimen, held by the South African Museum, supports the theory of African origin.
Once loose in a new environment, chytrid fungus can spread rapidly. "It can be spread by frogs – anything that moves through those water bodies, even other animals that visit those areas and researchers themselves," explained Katie. "You might walk into one site, jump in the car and accidentally transfer it to a healthy population."
You can help prevent the spread of chytrid fungus in a couple of ways. Firstly, says Katie, "never move a frog, tadpoles or eggs that you find in one area to another area, because you don't know which populations may have the chytrid fungus." Frogs are protected in Australia which means that you cannot legally catch, remove or relocate them; the threat of chytrid fungus is another good reason to leave them where they are. Frogs often hitchhike from Queensland in bunches of bananas, so if you find a stowaway in your supermarket, follow the instructions of the Victorian Frog Group and never release the frog into the wild.
Katie continued, "secondly, if you're moving between water bodies, wash your shoes really well and anything else you put in water." The Alps Bioscan teams bleached and scrubbed shoes and equipment between each aquatic field site, and Katie's frog team wore fresh surgical gloves when handling each frog.
The results from the survey and chytrid tests will be available later this year once the researchers have completed their analysis.
Ché Weldon, Louis H. du Preez, Alex D. Hyatt, Reinhold Muller,and Rick Speare. Origin of the Amphibian Chytrid Fungus, Emerg Infect Dis. 2004 December; 10(12): 2100–2105.