A development of a new form of fungus could explain the mystery of amphibian die-offs throughout the world, a large group of scientists now believes. Amphibians on six continents - Africa, South America, Central America, North America, Europe, and Australia and Oceania - have been reported as infected by the amphibian chytrid fungus.
Amphibians, such as frogs, toads, salamanders, and newts, act as sentinels for global environmental degradation, and over the past 30 years, amphibian population declines have been reported around the world.
This is the first wildlife disease to emerge on a global scale that affects an entire class of vertebrates and is associated with mass mortalities, population declines, and species extinctions, according to Peter Daszak of the Institute of Ecology, University of Georgia.
An international effort is now underway to determine how extensive and virulent the chytrid fungus is.
The fungal disease chytridiomycosis was first described in 1998 from the study of adult amphibians collected at sites of mass deaths in Australia and Panama from 1993 to 1998.
Meanwhile, to protect remaining amphibians, countries and zones within countries should be classified as free of or infected with chytridiomycosis, an international group of amphibian experts recommended last August after a workshop in Australia.
A case detection and recovery is unfolding in Colorado as state wildlife biologists use tiny high-tech transmitter locators to help boreal toads fight the deadly fungus.
Colorado amphibian researchers have found that the chytrid fungus is responsible for the decline of boreal toads usually found around the state's beaver dams and meadows.
For decades, their disappearance mystified Colorado biologists. The devastating losses appear to have started in the late 1970s and continued through the early 1980s. During that period, Colorado Division of Wildlife biologists estimated that as much as 85 percent of the state's boreal toad population was wiped out. Unlike many species whose decline could be related to the loss of habitat, there were no obvious changes in many of the places boreal toads inhabited. Yet from 1986 to 1988, the number of known boreal toad breeding sites fell from 59 to 10.
Then in 1999, while working with Dr. David Green at the National Wildlife Health Center, Colorado Division of Wildlife researcher Mark Jones discovered the existence of a chytrid in Colorado and linked it to the toads.
"Normally these chytrid fungi just live off of dead plant material and are fairly common," Jones said. "But apparently they have evolved into a new species of fungus that attacks living amphibian flesh. By the mid-80s it appeared that (the toads) were well on their way to extinction, but now we're finding a couple of new sites every year," Jones said. "Part of the reason is our intensified surveying efforts, so whether or not they will survive in the wild is still in question."
While the toads have not made much of a comeback, at least the populations may have stabilized, according to Jones. This spring and early summer, Jones was able to find toads at 56 sites, leading him to believe that their chances of long-term survival are improving.
In the meantime, Colorado biologists have established a breeding population of more than 1,000 toads at the John Mumma Endangered Species Hatchery in the San Luis Valley that will be used to repopulate areas that once supported boreal toad populations.
"We have captured toads from 18 different sites to guarantee genetic diversity," said Craig Fetkavich, a Colorado biologist who is overseeing the effort. Boreal toads don't reach sexual maturity for four-to-six years, Fetkavich said, so he is now in the process of artificially manipulating the hours of sunlight the toads receive to see if it is possible to speed up the age at which they can start producing young.
Once that happens, potential sites will first be tested for the presence of chytrid fungus. Those sites that are clean will be used to reintroduce the toads, who will be monitored to evaluate their recovery.
At this point it appears the fungus is not wiping out amphibian populations but only suppressing them. The ability of the toads to develop a natural defensive mechanism to combat the fungus remains to be seen.