December 13, 2010

A Frog Revival

Filed under: Adaptation, Animals

About 15 to 20 years ago, folks began to notice problems in amphibian communities around the world. At first, physical deformities were being noticed and then large population declines were being documented.

The finger was initially pointed at the coal industry, with an idea that perhaps mercury was leading to the deformities. But this didn’t pan out. Next, farm practices came under fire, as excess fertilizer running off into farm ponds became the leading suspect. But that theory didn’t hold water either. Then, attention turned to the ozone hole, with the idea that increased ultraviolet radiation was killing the frogs. No luck there either.

Then came the Eureka moment—aha, it must be global warming!

This played to widespread audiences, received beaucoup media attention and, of course, found its way into Al Gore’s An Inconvenient Truth.

But, alas, this theory, too, wilted under the harsh glare of science, as new research has now pretty definitively linked an infection of the chytrid fungus to declines, and even local extinctions, of frog and toad species around the world.

Perhaps the biggest irony in all of this, is that while researchers fell all over themselves to link anthropogenic environmental impacts to the frog declines, turns out that as they traipsed through the woods and rainforests to study the frogs, the researchers themselves quite possibly helped spread the chytrid fungus to locations and populations where it had previously been absent.

Now a bit good—although hardly unexpected—news is coming out of the frog research studies. Some frog populations in various parts of the world are not only recovering, but also showing signs of increased resistance—gained through adaptation and/or evolution—to the chytrid fungus.

Thus opens a new chapter in the ongoing Disappearing Frog saga, and one that likely foretells of a hoppy ending.

The magazine New Scientist has an interesting article titled “Fungus out! The frog resistance is here” that ties together a growing number of research findings indicating that frog populations that once faced local extinction have been making a come back—even in the continued presence of the chytrid fungus.

New Scientist reports that Australian researchers are reporting that a variety of frog species from across the Land Down Under that were once devastated by chytrid infection are now re-establishing themselves in areas that they were wiped out and in some cases have even returned to numbers as large as they were prior to the chytrid outbreak.

Other researchers are finding, as reported in the Proceedings of the National Academy of Sciences (Briggs et al., 2010), that frogs in the mountains of California that were once “driven virtually to extinction” are also making a recovery even though the chytrid fungus is still present. Some populations there have apparently developed the ability to survive in the presence of low-levels of the fungus.

Evidence of a developing resistance to the chytrid fungus has also been reported in a species of Australian frogs. A study published in the journal Diversity and Distributions (Woodhams et al., 2010) looked at populations of frogs which have recovered from a chytrid infection and found indications that natural selection may have led to more resistant populations and facilitated the recovery.

All this is not to say that amphibian populations across the world have made a full and complete recovery, but it is to say that there are encouraging signs that some populations are clawing their way back through adaptation and natural selection—precisely the way things are supposed to work.

And even though global warming is no longer considered to be the guilty party (of course, exonerated with much less fanfare than it was accused), the amphibian story does show the resiliency of nature—a resiliency that is grossly underplayed or even ignored in virtually all doom and gloom presentations of the impacts of environmental change.

Something that is worth keeping in mind.

References:
Briggs, C. J., et al., 2010. Enzootic and epizootic dynamics of chytrid fungal pathogen of amphibians. Proceedings of the National Academy of Sciences, 107, 9695-9700.

Woodhams, D.C., et al., 2010. Adaptations of skin peptide defenses and possible response to the amphibian chytrid fungus in populations of Australian green-eyed treefrogs, Litoria genimaculata. Diversity and Distributions, 16, 703-712.




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