Global Amphibian Declines: Researchers complete first major survey of amphibian fungus in Asia

From 2001 to 2009, the team surveyed more than 3,000 amphibians -- mostly frogs -- from 15 Asian countries, searching for any trace of the disease infecting the skin of the amphibians. The survey could help scientists to answer the question why the Chytrid fungus has been unusually devastating in many parts of the globe -- and why rapid population declines and extinctions are apparently absent in Asian amphibians.

The globally emerging disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis or Bd, is next to habitat destruction one of the major driving forces in amphibian extinctions in Central, South and North America, Australia and Europe. The new Asian survey of the fungus, which was published Aug. 16 in the journal PLoS One by Andrea Swei, Cary Institute of Ecosystem Studies, NY, USA, and colleagues, shows that Bd is prevalent at very low levels in the region.

“The study shows that ongoing research of the Zoologisches Forschungsmuseum Alexander Koenig - Leibniz Institute for Animal Biodiversity is very important for the conservation and inventorying of the global amphibian fauna” says Prof. Dr. Wolfgang Wägele, scientific director of the Forschungsmuseum Koenig.

“Amphibian diversity in Asia is very high and many of the frogs, toads and salamanders could potentially be vulnerable to Bd” Dennis Rödder, Curator for Herpetology at the Zoologisches Forschungsmuseum Alexander Koenig, Bonn, Germany, explains. “Unfortunately, we know very little about the fungus and its impact on the Asian biodiversity.”

"That's why we're excited about this first really big survey," says Vance Vredenburg, assistent professor at the University of California, Berkeley and leader of the research team. "If you look at chytrid worldwide, Asia's been the black hole in our data."

“Previous attempts to assess the potential distribution of the chytrid on a global scale already highlighted the high possibility that it might occur in huge parts of Asia” Rödder said. “The new data now allow s to assess the predictive abilities of our previously developed global extinction risk assessment for more than 6,000 species, which was published in 2009 in the Journal Diversity” .

From 2001 to 2009, the team surveyed more than 3,000 amphibians -- mostly frogs -- from 15 Asian countries, searching for any trace of the disease infecting the skin of the amphibians.

Thei results suggest that the prevalence of Bd was very low throughout the study sites, appearing in only 2.35 percent of the frogs. The Philippines, Kyrgyzstan, Laos, Indonesia, Malaysia and South Korea were the only countries with any Bd infection.

“The distribution pattern of the chytrid in Asia is very patchy and therefore somewhat strange compared to its wave like emergence in other parts of the world” Rödder explains. “The new findings may indicate that Bd is either just emerging in Asia, or may have been in Asia at low levels for a long time” Alternatively, some other factor is preventing Bd from “fully invading Asian amphibians" the researchers write.

Due to the huge geographic coverage of the study, each site was only surveyed once and long-term observations are almost completely lacking, the researchers explained, so it's difficult to determine whether Bd infections in the countries are newly expanding. “It will be critical”, Vredenburg said, "to see how Bd prevalence is changing through time, because this is key to understanding the ultimate outcome of the disease."

If Bd has been in Asia for a long time, researchers would like to know why amphibians there have managed to co-exist with a fungus that has proved so destructive elsewhere. It is possible, for instance, that Asian amphibians might bear some sort of bacterial protection against Bd in their skins.

Other scientists are analyzing the genes of the Bd fungus collected globally, Vredenburg said, "to find out whether strains from different parts of the world also differ in their virulence."

And if Asia is on the brink of a chytrid epidemic, Swei and colleagues think it might start in the Philippines. "The prevalence and intensity of Bd infection is much higher here than anywhere else in Asia," she said. "Bd in the Philippines today looks similar to Bd in early outbreaks in California and South and Central America."

“This study is the first important step to understanding Bd in Asia," Vredenburg said. "It provides a solid foundation that future studies can build upon."

“The study has strong implications for the coordination of future conservation efforts”, Rödder said. “The possibility of another wave of extinctions as already observed in Central and South America highlights the need to follow the Asian survey with further monitoring programs. These are pivotal for emergency responses, such as captive breeding programs, which could save some species from extinction.”

Swei A, Rowley JJL, Rödder D, Diesmos MLL, Diesmos AC, et al. (2011) Is Chytridiomycosis an Emerging Infectious Disease in Asia?

PLoS ONE 6(8): e23179. doi:10.1371/journal.pone.0023179