March 25, 2008
Zoologists unlock new secrets about frog deaths
CARBONDALE, Ill. — New research from zoologists at Southern Illinois University Carbondale opens a bigger window to understanding a deadly fungus that is killing off frogs throughout Central and South America, and that could threaten amphibian populations in North America as well.
The research, led by SIUC zoologist Karen R. Lips, and SIUC zoologist Michael W. Sears, underscores the dire circumstances facing up to 43 percent of known amphibian species in the world and points up the need for more regulations, conservation efforts and quarantines to prevent the fungus' spread.
A paper outlining their findings appeared today (March 25) in the journal PLOSBiology.
An associate professor of zoology in the College of Science at SIUC, Lips is at the forefront of in research in catastrophic decline of frog species brought on by the Batrachochytrium dendrobatidis fungus. The fungus, known to researchers as "Bd," wipes out frog populations essentially by completely blocking their skin. Amphibians such as frogs depend on their skin to provide oxygen and moisture. Bd infections cause electrolyte imbalance, which can lead to cardiac arrest.
Lips has studied the issue since the early 1990s, becoming a recognized expert on the subject. She, along with her graduate and doctoral students, regularly visit the high jungles of Central America, roughing it in the wild while collecting data on the ecological systems before, during and after the fungus arrives.
This latest study, conducted with Sears, an assistant professor of zoology at SIUC, and two other colleagues at the Illinois Natural History Survey and Zoo Atlanta, expands upon that work by seeking better understanding of the spread of the fungus, its triggers and how it might be spread.
Specifically, the researchers examined data from South American amphibian declines to see whether the wave-like spread seen in Central America, typical of an emerging infectious disease, was evident.
One previous theory, for instance, blamed the fungus on global climate change. Lips and Sears, however, found climate change doesn't appear to trigger outbreaks of the fungus, but that it instead spreads in wave-like patterns often seen in exotic species and emerging infectious diseases. They call their theory the "spreading pathogen hypothesis."
Using modeling, the researchers found evidence of four different introductions of Bd into South America. They found that the fungus spread through the population at a rate similar to that seen in Central America and in a manner that best explains amphibian population declines in Central and South America.
"What makes the study really relevant is we can now generalize how the fungus is spread," Lips said. "We know from our research, that if we start looking in the right time and place in an area where the fungus is, we're probably going to see it affecting frog populations. This helps us understand what's going on, and it can potentially help us get out in front of it."
The study could help governments and environmental agencies focus on ways to prevent the fungus' spread through more regulation of potential infection routes, such as the ornamental plant and aquarium wildlife trade. The fungus can easily hitch a ride to other regions through such trade, Lips said.
"If you go and buy an ornamental plant from one of these regions and plant it in your yard, or you buy a frog at a pet shop, think about it. If the fungus is there and still alive, it's now introduced into the environment. Then it can get into your pond or streams."
Lips said simple testing of such products and organisms before importing them could reveal the fungus' presence. Once discovered, simple anti-fungal drugs will kill the fungus before it can contaminate an area.
"Our research has shown that once the fungus gets somewhere new it spreads like wildfire," Lips said. "So the key is preventing it from spreading."
The fungus is present in North America, including Illinois, but little is known so far about its impact here. With funding from the Illinois Department Natural Resources, Lips in the coming months will survey the extent of the fungus and its impact in Illinois.
Among the study's key points:
• Climate change, while having some negative impacts on amphibian biodiversity, does not appear to have triggered the disease in Central America and the Andes of South America, as suggested by previous studies.
• The fungus appears to have spread in a wave-like manner, in a typical pattern of disease spread.
• The fungus was introduced in South America in the late 1970s or early 1980s. After introduction, the disease spread along the Andes, infecting native amphibians and often causing the extinction of entire populations and species.
• There is robust evidence supporting the "spreading pathogen hypothesis," which holds the disease was and continues to be spread in a wave-like pattern seen in Central America. It is likely this same pattern will emerge in other places where Bd has been detected, including North America and Europe.
Lips said the study increases understanding of the disease, which should allow humans to take steps to limit its spread.
"We need to get into areas ahead of the spreading wave — such as eastern Panama and the southern Andes — to conduct intensive surveys and monitoring for both native amphibians and the … fungus," Lips said. Environmental agencies also should immediately begin conservation programs aimed at conserving rare and endangered amphibian species that might be wiped out by the fungus.
"At this time, the fungus cannot be controlled or managed in wild amphibians nor their habitats," Sears added.
The island of Madagascar, which is home to a large number of plants and animals found nowhere else in the world, so far appears free of the deadly fungus. The researchers said governments should take steps to maintain that status.
In the future, Lips believes that researchers should study treatment options for wild amphibians and possibly their habitats to prevent or minimize the fungus while establishing a global network of disease surveillance. They should increase communication and monitoring of global trade and increase outreach communication with researchers and policy makers to raise awareness on its potential impacts in other geographic locations.
Researchers also should survey museum specimens to better determine the location, timing and possible sources of the fungus and its introduction into the environment in various locations. They also should study fungus samples for genetic clues as to its origins and the different strains involved.
Solving a mystery – Karen R. Lips, right, an associate professor of zoology at Southern Illinois University Carbondale, and Micheal W. Sears, assistant professor of zoology at SIUC, examine a live frog specimen in a laboratory at the Life Science II building on the SIUC campus. The two researchers recently helped complete a study that opens a wider understanding on how a fungus that is wiping out frog populations is spread.
Photo by Jeff Garner