New findings may help ecologists understand the spread of a deadly fungus decimating amphibian populations worldwide.

A group of fungi called chytrids, which includes a frog-killing pathogen, dominates soil communities in otherwise relatively lifeless habitats atop mountains in the Rockies and in Nepal, where water and multi-cellular life is often scarce, researchers report. Though these assemblages did not include the infamous Batrachochytrium dendrobatidis (BD), which has hammered global amphibian populations for at least a decade, researchers say that learning about the enigmatic chytrids may shed light on why the pathogen seems to be so widespread.

University of Colorado, Boulder, microbial ecologist Steve Schmidt sampling chytrid-rich soil in Nepal Image: Debendra Karki

"This gives us a better picture of what chytrids do and where they are," said University of Maryland ecologist Karen Lips, who studies amphibian and reptile declines in Central and South America but was not involved in the current study.

"When I first read this paper, I thought, 'If all these chytrids are up there, maybe the one that's attacking frogs is up there too,'" she said. "I'm almost surprised that they didn't find it." Lips told The Scientist that researchers should now search for BD in similar high-elevation environs to get a better handle on how the deadly fungus spreads from habitat to habitat. "These environments seem to be a good place for chytrids in general," she said. "Maybe this does shed some light on where BD came from."

"We were not expecting to see chytrids as the dominant eukaryotic life forms in those soils," Steve Schmidt, the University of Colorado, Boulder, microbial ecologist who led the study, told The Scientist. "These kinds of chytrids seem to be easily dispersed, probably by the wind." That would account for the fact that Schmidt and his colleagues found similar assemblages of chytrid species in places as far separated as Colorado and Kathmandu. They present their findings in this week's issue of the Proceedings of the National Academy of Science.

Joyce Longcore, a University of Maine mycologist and a coauthor on the study, agreed that finding a community dominated by chytrids was surprising, but cautioned against jumping to conclusions about BD based on these data. "Because there was so little obvious organic matter up there, it was surprising" to find chytrid fungi dominating, she said. Longcore explained that chytrid RNA sequences dominating eukaryote communities more than 3,500 meters up on remote mountaintops probably came from asexual "resting structures," or spores, common to many fungi. These spores can typically withstand extreme desiccation and are often dispersed by the wind.

"Just because most [chytrids] have resistant spores doesn't mean they all do," Longcare said. But, she added, "I'm still not willing to rule out the possibility that there are resting structures [in BD], but we just have not seen them yet."

Finding eukaryote communities dominated by chytrids at higher elevations does mesh with some of Lips's observations in Central and South America, where chytridiomycosis (the disease caused by BD) is rampant. She said that at her study sites in Panama and Costa Rica, a few hundred meters in elevation can make a huge difference on how rapacious chytridiomycosis is. She noted that some 1900 meter peaks are essentially devoid of frogs, their populations decimated by the fungus, while just 1000 meters down the mountain, some chytrid-free frogs can still be found. "The higher elevation sites are much more affected than the mid or low elevation sites."


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