Green Blog: Mapping a Plague of Frogs

One of the first things that epidemiologists do when studying a new outbreak of disease is to map its occurrence. From there, they try to tease out patterns related to the malady?s cause and prevalence, and begin working on solutions to quell it.

For tracking sick frogs, toads and salamanders, it turns out that the same principle applies. Researchers have assembled an interactive map documenting the global emergence of Batrachochytrium dendrobatidis, the amphibian chytrid fungal disease that is blazing through populations of water-dwelling animals around the world.

Scientists are still struggling to understand this plague, regarding it as a major threat to the survival of many amphibian species. The research team hopes that the map will bring together fragmented research efforts and present an overarching picture of the problem.

Deanna Olson, a research ecologist at the Forest Service?s Pacific Northwest Research Station in Oregon, and her colleagues are ebullient over their success in assembling a world network of scientists and managers that are interested in conducting real-time surveillance. ?This is allowing us to track what we know about this disease, which has been implicated in mass mortality events as well as some extinctions at the global scale,? she said.

Along with colleagues from Imperial College in London and Oregon State University, Dr. Olson and her lab have developed an online database that currently holds more than 36,000 records of individual animals sampled in over 4,000 sites around the world. Plotting that data geographically allows the team ? or any other interested party ? to see where the fungus is and is not present, and where it has or has not been tested for yet.

Anyone can upload their data to the site, and Dr. Olson?s team updates it annually to make sure it reflects the latest findings in the field. The project, called Bd-Maps, got under way in 2008 and is described this week in the journal PLoS One.

The maps visualize data on both a global and individual country scale. Sampling sites are marked with pins that are color-coded to indicate whether the amphibians tested there turned out to be positive or negative for the disease. This allows scientists and wildlife managers to glean a quick understanding of how their area?s amphibians fare as a whole.

From this data, researchers can also extrapolate the odds of the disease occurring in any given location, and the level of threat that species in those locations may face. (The fungus does not affect all amphibians equally.) ?In some places chytrid fungus is a huge problem, but in other places it doesn?t appear to be such a problem,? Dr. Olson said. ?For example, in the U.S. there has only been a handful of mortality events, but places like Central America and Australia are experiencing a lot of mass mortality and even extinctions.?

The map does have a few potential shortcomings. At this point, the team accepts any data submitted; there is no formal process of standardization or validating that the the data comes from reputable experts. That means that some places could turn up with false positives or false negatives for the disease.

Because the map does include so much data, however, the researchers think it still paints a fairly robust picture of the situation on the ground. The team is also applying lessons learned from this project to create a new, more stringently screened map of the occurrence of ranavirus, another disease that affects amphibians.

Dr. Olson and her colleagues designed the chytrid fungus map as a community tool for others to explore and work with, but the team has uncovered some initial findings on its own. According to their data, 42 percent of 1,240 species sampled worldwide turned up positive for the fungus. There are more than 6,000 species of amphibians, so this means that just 20 percent have been sampled for the disease to date. From the 82 countries sampled so far, 68 percent came back with positive results.

Temperature range stood out as a driver of fungus presence, with places that experience less fluctuation between their hot and cold seasons being more likely to be heavily afflicted by the disease. Dr. Olson hopes that other researchers will investigate whether this large-scale pattern also fits at the local scale.

Already, Bd-Maps is generating interesting collaborations in the field. Dr. Olson said that the map has inspired some researchers to sample new locations in the central United States, for example.

?People have looked at our maps and seen that nobody?s reported on chytrid fungus here or there, then they?ve gone out to do a study to fill in the map,? she said. ?It?s like we?re playing a game of Risk ? we?re always excited to get a new place filled in, especially if it?s in a remote area.?

In other cases, researchers have used the map as a matchmaking service for chytrid fungus aficionados. An Armenian researcher recently used Bd-Maps to reach out for on-the-ground support, for example, and a scientist visiting Papua New Guinea obtained the necessary training to test for chytrid through contacts found though the the site.

?We don?t often see this type of collaboration in the research world, which is classically very much an ivory tower,? Dr. Olson said. ?We?re really excited that our project is being used at the global scale to investigate new hypotheses and patterns emerging from the data by a variety of biologists and managers.?

Source: http://green.blogs.nytimes.com/2013/02/27/mapping-a-plague-of-frogs/?partner=rss&emc=rss

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