THE WORLDWIDE crash in amphibians probably doesn鈥檛 have a single cause.
Increased UV radiation, pollutants, and infections from pathogens could all have
a role in the animals鈥� demise, say scientists.鈥滻 don鈥檛 think there鈥檚 going to be
a simple answer,鈥� says zoologist Andrew Blaustein of Oregon State
University.
Increased UV radiation is killing off the Cascade frog (Rana
cascadae) and the Western toad (Bufo boreas) in the Pacific
Northwest of the US. But the Pacific tree frog (Hyla regilla) seems
immune to UV, probably because it has higher levels of photolyase, an enzyme
that repairs damaged DNA. It may be that UV makes amphibians vulnerable to other
attacks, Blaustein says. For instance, amphibians hatched in UV light and
exposed to the fungus Sapholocnia die much more quickly than those
exposed to only one or the other.
Another possible cause of the crash is infection with the Chytrid
fungus. Since its discovery only four years ago, the fungus has turned up in
frogs all over the world, says Elizabeth Davidson, a biologist at Arizona State
University. Other fungi and viruses have also been associated with massive
die-offs. But Davidson says it鈥檚 not clear if the diseases are new, or if it鈥檚
that amphibians now have weakened immune systems, making them more susceptible
to disease.
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If global climate change is to blame, it鈥檚 not yet obvious how, says Cynthia
Carey, a biologist at the University of Colorado. Amphibians have adapted to
extreme climate change in the past, but it could intensify other problems, such
as creating a perfect environment for fungi.