A new fungal disease appears to be responsible for mass deaths in frog populations in Australia and Panama.
Australian researchers from CSIRO Australian Animal Heath Laboratory in Geelong and James Cook University in Townsville were first to find the new fungus in 10 frog species and have shown that the fungus kills frogs in laboratory trials.
A similar fungus was found on amphibians in Panama last year.
In the last two decades there have been many reports of frog population crashes around the world. Some are clearly due to pollution and other environmental changes. The idea has emerged that frog disappearances are an early indication of environmental degradation.
The areas where this fungus was found include areas that are "pristine". Population crashes have been observed here in relatively pristine areas of tropical Queensland rainforest. Similar sudden declines have occurred in protected mountainous rainforest areas in Central and South America.
An international team of scientists has been collaborating to solve this problem. The Australians have been working with researchers in the UK and USA. They've found evidence that a new fungal disease is causing mass mortalities in amphibian populations in both Australia and Panama. In 1993 the suspect was first found in Australia at the Melbourne Zoo and in the wild in forests near Cooktown in Northern Queensland.
Dr Lee Berger and Dr Alex Hyatt, from CSIRO AAHL in Geelong began investigating the issue in 1995 with Dr Rick Speare, from James Cook University, Townsville.
"We found that this fungus invades the superficial layers of the skin, causing damage to the keratin layer on the skin surface," says Dr Berger. "As frogs drink and breathe through their skin, the fungus may kill the frogs by disrupting these mechanisms"
"The fungus is a new species of aquatic chytrid fungi, which is yet to be named. Chytrid fungi have not previously been found to parasitise vertebrates before. Other types of chytrid fungi can live freely in the water or soil, and there are some that are parasites of plants and insects," says Dr Berger.
Dr Peter Daszak, Kingston University Surrey in the UK and Dr Louise Goggin, CSIRO Marine Research, Hobart identified the fungus using electron microscopy and molecular biology. Berger and Hyatt then demonstrated that it could infect and kill frogs. Strangely, tadpoles do not succumb to this disease. This fits with field reports where tadpoles have been seen in areas after the adults have disappeared. About 2- 3 weeks after metamorphosing, young frogs have been found dying.
Their US colleagues have found the same fungus in frogs in many zoos and have retrospectively shown it was present in one zoo as early as 1988.
Investigations are continuing - to confirm the hypothesis, and work out how this disease has emerged to become significant. It is possible that it has been introduced to these areas, or that environmental changes have made the frogs susceptible. Further studies are also needed to determine how closely related are the fungi from different areas and whether they are all the same species.
The success of this investigation has been due to the collaboration of scientists with different areas of expertise, and from different countries. The team includes:
- Dr Lee Berger, CSIRO
- Dr Alex Hyatt, CSIRO
- Dr Rick Speare, James Cook University, Townsville
- Dr Peter Dasak, Kingston University Surrey UK
- Dr Andrew Cunningham, Institute of Zoology, London UK
- Dr David Green, NIH Maryland USA
- Dr Karen Lips, University of South Illinois USA
- Keith McDonald, Queensland Department of Environment
- Harry Hines, Queensland Department of Environment
A scientific account of the investigation will be published next month in the prestigious US scientific journal, Proceedings of the National Academy of Sciences.
Background information including photographs of the frogs is available at www.ah.csiro.au
Journal
Proceedings of the National Academy of Sciences