science

On June 3 at the Smithsonian, a larger-than-usual crowd showed up at the Tuesday noontime free science lecture to hear University of Georgia botanist David Porter talk about emerging diseases that take their tolls on nature.

Most of the people who attend these presentations consider humanity to be a part of nature, and thus would readily understand the implication that the grain blights, seaweed die-offs, golf course plagues and so forth that Porter studies under electron microscopes have their analogues in emerging human diseases like SARS and AIDS. But Porter is not an ecologist or even an epidemiologist and though he acknowledged the wider questions he concentrated on the "micro" parts of the larger pictures of several diseases that are sweeping through wild populations of fauna and flora.

Of the greatest ecological, cultural and economic importance to Panama was that part of Porter's discourse on the disease that's wiping out the golden frogs in their highland habitats.

For several years now there have been big declines in regional highland frog populations, beginning in Guatemala and moving down the Meso-American isthmus to Panama. Ecologists have expressed concern that frogs might be "indicator species" like the proverbial mineshaft canaries, and that the population declines might have something to do with global warming or some widesrpread human offense against the natural realm.

A major break in the investigation happened at the National Zoo in Washington, DC, when an arrow poison frog was found to be infected with a fungus. It was Betrachochitrium dendrobatidis, one of the chytri d fungi that are known as parasites or saprophytes on algae and microinvertebrates. Further investigation showed that the fungus, once thought to be rare, is associated with declining frog populations around the world. (But not all such die-offs -- - another emergent amphibian malady, ranaviral disease, is also at large among many of the world's frog populations.) In Panama, the fungus has been linked to the golden frogs' decline. Despite these correlations that have been found, scientists do not yet know how the fungus affects the frogs.

According to DNA analyses cited by Porter, the various strains of Betrachochitrium dendrobatidis found in places as scattered as Maine, Australia and Panama don't particularly correspond to any geographical pattern. He does note, however, the highland frog species are far more affected than their lowland cousins. He says that the DNA evidence suggests that the chytrid plague has spread among the world's frogs relatively recently, but because very little is known about the life cycle of the fungus --- for example, how it survives and reproduces when its frog hosts have been wiped out --- "it's basically just arm-waving at this point."

Two hypotheses that Porter noted are that commercial bullfrog farming has spread parasites around the world, or that the fungi had been living harmlessly in the environment until some environmental stress factor made the frogs vulnerable to infections.

The botanist made it clear that he just doesn't know, and offered a case of champagne to any biologist in the audience who discovers how Betrachochitrium dendrobatidis survives when in a natural environment and unattached to frogs. Part of the problem, he said, is that little research has been done on chytrid fungi. However, the bright side of that is that some of the people who came to the lecture might find grant money readily available to do the research that can fill in the gaps in our knowledge of the decline in Panama's golden frogs.

Also in this section:
Solving the mystery of the golden frogs' decline
Traditional medicine

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