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CORVALLIS -
Zoologists at Oregon State University presented the first major
field study which concludes that the levels of ultraviolet, or UV-B,
radiation now found in sunlight can cause physical deformities in
amphibians, a problem that has alarmed researchers around the world.
The findings
were announced in the journal Proceedings of the National Academy of
Sciences.
They confirm
prior lab studies done on this topic, scientists say, and may serve as
an ominous early warning of some of the real impacts of global climate
change.
In this
experiment, which was done with long-toed salamanders in lakes of the
central Oregon Cascade Range, more than 90 percent of the salamander
embryos that were not shielded from UV-B radiation either died or
hatched with deformities.
By comparison,
almost all of the embryos protected by special filters from the UV-B
radiation levels that are currently present in sunlight survived and
were perfectly normal.
"The
findings were astounding to us," said Andrew Blaustein, an OSU
professor of zoology and expert on amphibian declines around the world.
"The point to remember is that these were not artificially-elevated
levels of UV-B light or results from a laboratory. These salamanders
were exposed to nothing more than ambient, natural levels of sunlight
while living in their normal habitat.
"The
salamander embryos that were not protected from natural sunlight mostly
died," Blaustein added. "The few that managed to survive were
almost always deformed."
Other possible
causes of amphibian deformities which have been proposed, such as
attacks by certain parasites or exposure to pesticides, were not present
in this field experiment, Blaustein said. This suggests that UV-B
exposure, by itself, is adequate to cause high levels of death or
deformity in some species. But it does not preclude the possibility that
other forces, including parasites or pesticides, may be relevant in
other areas, or that combinations of the various causes may sometimes be
at work.
The global
decline in amphibian populations, and more recently the disturbing
number of deformed amphibians, have caused many researchers to believe
they may be an early indicator of serious environmental problems. At
various locations, acid rain, habitat destruction, pollution, predation
and other factors have all been implicated in amphibian declines, and
disappearing species have been found from Europe to North America,
Australia, Asia, Africa and elsewhere.
One of the more
disturbing concerns, especially on a global scale, may be the role of
rising levels of ultraviolet light which are linked to depletion of
Earth's protective ozone layer. Such increases in UV-B radiation have
been demonstrated both in polar and temperate regions, Blaustein said -
including one Canadian study which found increased UV-B levels over a
five-year period at the same latitude as the recent experiments done in
Oregon.
In previous
studies, Blaustein and his colleagues demonstrated that natural levels
of UV-B radiation were causing high levels of embryo mortality in
several species of frogs, toads and salamanders.
The latest
research examined long-toed salamanders, partly because they were known
to have low levels of the enzyme photolyase, which plays a key role in
repairing DNA damaged by UV-B. This salamander in particular, and many
other amphibians in general, are vulnerable species because they have no
hair or feather protection, lay unshelled eggs and at various stages of
development may be exposed to a wide range of environmental insults.
But they also
have thrived since before the age of the dinosaurs.
In the OSU
study, some eggs in a Cascade Range pond were protected from UV-B
radiation, while others were not. Of those not protected, 85 percent
died and 92 percent of the survivors had some type of developmental
deformity, affecting their bodies, heads, eyes, tail, growth rate or
other area. Of those shielded from natural UV-B levels, only 5 percent
died and less than 1 percent had any deformities.
Dr.
Andrew Blaustein at a field site in the Cascade Mountains
Collaborating
on this study were scientists from Yale University, the University of
Maine, and the Oregon Cooperative Wildlife Research Unit of the U.S.
Geological Survey.
It's difficult
to project the findings of studies such as this to potential impacts on
other plant and animal species, Blaustein said. Many plants, insects,
mammals, birds and fish are sensitive to UV-B radiation. Among those
known to be the most sensitive are algae, some aquatic insects and fish,
coral, and ocean plankton, which forms the basis of the marine food
chain.
High levels of
ultraviolet light exposure in humans has been linked to cataracts,
immune suppression and skin cancer.
But beyond the
larger concerns for other species, Blaustein said, the declining
populations and disappearance of amphibians are a serious problem in
their own right. These frogs, toads, salamanders and other species have
survived for hundreds of millions of years - until now - and play key
roles in numerous ecosystems, often serving as both prey and predator to
other species.
"What
you're seeing here are profound deformities and death being caused in a
wild species by nothing more than the UV-B radiation levels now being
found in sunlight," he said. "In my opinion, studies such as
this suggest people should be taking concerns about climate change very
seriously. It's increasingly clear a lot of ecosystems are already
suffering significant impacts."
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