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No global warming link to dying frogs?

No global warming link to dying frogs?

No global warming link to dying frogs?
March 25, 2008

Scientists have fired another salvo in the heated debate over the role of climate change in the global decline of amphibians.

Writing in the March 25 issue of PLoS Biology, a team of researchers led by Karen Lips of Southern Illinois University-Carbondale report finding “no evidence to support the hypothesis that climate change has been driving outbreaks of amphibian chytridiomycosis” — a disease blamed for large-scale die-offs of amphibians. Other researchers have argued that climate shifts are worsening the outbreak of the fungal disease.

Instead Lips and colleagues say that multiple introductions of the invasive pathogen are responsible for outbreaks in South America. Their work is based on modeling of the geographic decline of colorful harlequin frogs (genus Atelopus) in Central and South America and showed that fungus-linked declines are spreading in a wave-like pattern typical of highly virulent epidemics and unaffected by climate variables.

Chytrid fungus (Batrachochytrium dendrobatidis)

Scientists don’t yet know the origin of the fungus, though they suspect that it might be the African clawed frog, a species that has been shipped around the world for research purposes. The fungus is highly transmissible and some have accused scientists of inadvertently introducing spores of the pathogen into ecosystems in the tread of their boots. In any case the fungus is now found on at least four continents and is spreading fast. Last April, Japan confirmed the first local frog deaths from the fungus, while in Panama, the fungus appears to be migrating at a steady rate across the isthmus.

“Our findings further strengthen the spreading-pathogen hypothesis proposed for Central America, and identify new evidence for similar patterns of decline in South American amphibians,” the authors write.

Other studies have found a similar pattern of decline in Eastern Australia.

Implications for conservation

Lips says the new study provides clues that could help limit the spread of the killer fungus.

“What makes the study really relevant is we can now generalize how the fungus is spread,” Lips said. “We know from our research, that if we start looking in the right time and place in an area where the fungus is, we’re probably going to see it affecting frog populations. This helps us understand what’s going on, and it can potentially help us get out in front of it.”

Lips says that since the fungus can be spread via the ornamental plant and aquarium wildlife trade, governments and environmental agencies should test on imports for the presence of the pathogen. Once discovered, anti-fungal drugs can destroy the fungus before it can contaminate an area.

Panama’s golden frog (Atelopus zetecki). Unlike other frogs, the Panama golden frog lacks eardrums and communicates by waving its hands. In many parts of Panama this frog is considered a good luck charm and people collect it from the wild to put in their homes. This custom further threatens a species already suffering from the killer chytrid fungus (Batrachochytrium dendrobatidis), an infectious skin disease now found in frog populations around the world.

The study reveals that the fungus is spreading in “a wave-like manner, in a typical pattern of disease spread.” First introduced in South America in the late 1970s or early 1980s, “the disease spread along the Andes, infecting native amphibians and often causing the extinction of entire populations and species.”

“Our research has shown that once the fungus gets somewhere new it spreads like wildfire,” Lips said. “So the key is preventing it from spreading.”

“At this time, the fungus cannot be controlled or managed in wild amphibians nor their habitats,” added co-author Michael W. Sears, also a zoologist at Southern Illinois University Carbondale.

The bigger picture

There are 6,000 known species of amphibians — cold-blooded animals that include frogs, toads, salamanders, newts and caecilians — worldwide.

Globally, 43 percent of amphibian populations are in decline according to the Global Amphibian Assessment. Other studies have cited habitat loss, pollution, pesticide-use, increased UV-B radiation, and the introduction of alien invasive species as possible factors in the decline.

In recognition of their plight, the “Amphibian Ark” — a coalition of zoos, botanical gardens and aquariums — has designated 2008 as “The Year of the Frog”. Amphibian Ark is seeking to raise $50-60 million as part of a 5-year $400 million Amphibian Conservation Action Plan to establish captive breeding programs for the 500 most threatened species.

Lips, K.R. et al (2008). Riding the Wave: Reconciling the Roles of Disease and Climate Change in Amphibian Declines. PLoS Biology Vol. 6, No. 3, e72 doi:10.1371/journal.pbio.0060072

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