From
North Forty News
By Gary Raham
Spring has to be the best of seasons: The fresh smells of
rain-wet juniper; blue pasque flowers backlit with morning
sunlight along mountain trails; frog choruses at moonrise...
Although, frog choruses are becoming rare these days. Ponds
where I collected tiger salamander larvae 15 years ago have
dried up or been developed over. Amphibians, an ancient
line of vertebrates that have survived several mass extinctions
over the last 350 million years, continue to decline worldwide.
Victims include golden toads in Costa Rica, yellow-legged
frogs in the Sierra Nevadas, spotted frogs in the northwestern
United States and many others. Often, surviving populations
contain many malformed individuals --up to 80 percent in
some areas. Since 1995, 60 species in 46 states in the United
States typically contain individuals with missing limbs
or extra ones, making them more prone to predation.
We like to find single causes for such things. Single causes
can be fixed. Too much radiation because CFCs are zapping
the ozone layer? Eliminate freon from refrigerators. Poisoning
from agricultural runoff? Develop safer fertilizers and
pesticides. Rogue diseases? Find a new "magic bullet."
In fact, amphibian malformations and die-offs illustrate
what first became a truism in the '60s and '70s: We're all
caught in one big sticky and elaborate web of life. Pluck
one strand and everything shivers.
Scientists continue to piece together the decline and transformation
of Kermit and his relatives, and it's a tale worthy of a
CSI episode. Radiation became suspect number one, largely
because scientists, aware that ozone in the upper atmosphere
had been declining since the '70s, knew that the increased
ultraviolet radiation reaching Earth's surface could cause
genetic mutations and immune system damage in animals. Studies
performed in the mid- to late '90s showed that UV radiation
could indeed kill amphibian embryos and larvae, cause serious
eye damage in adults and induce certain kinds of deformities
in frogs and salamanders--although not the kinds of multiple
or missing limbs most often found in nature.
Other researchers turned to suspect number two: toxic chemicals
like methoprene. Methoprene, first approved for commercial
use in 1975, replaced DDT, the pesticide indicted in Rachel
Carson's 1962 book, "Silent Spring." Methoprene,
unlike DDT, breaks down fairly quickly in the environment,
but chemically it is similar to retinoic acid, a compound
important in vertebrate development. Too little or too much
can cause deformities. Pregnant women are advised not to
use acne medicines, which contain a retinoic acid derivative,
because they are linked with miscarriages and birth defects.
Methoprene may, in fact, break down fast enough that it
is not a likely suspect in amphibian decline, but it is
one of over 61 other agricultural chemicals, most untested.
Suspect number three, a parasitic flatworm, came to light
in California with the discovery of large numbers of Pacific
tree frogs and long-toed salamanders with missing legs,
extra legs and other deformities. Scientists discovered
that the cysts of these worms, implanted near limb bud regions
of the amphibians, caused the deformities. Glass beads implanted
in the same regions caused the same kinds of deformities
with the same frequency.
But the California studies also highlighted how all the
suspects collaborated in a tangled web of intrigue--and
life. They (and we) are all guilty. Here's how it works:
Human industrial activity produces CFCs which deplete atmospheric
ozone, allowing increased UV radiation to kill or weaken
amphibian populations. Agricultural activity produces runoff
rich in nitrogen, which promotes algal growth in ponds and
lakes. The algal growth stimulates snail growth, and snails
are the intermediate hosts of the worms that cause limb
deformities. Amphibians with deformed limbs are more apt
to be eaten by predators. Human land development also isolates
amphibians into small populations more easily destroyed
by random disasters and normal population fluctuations.
In the 19th century miners took canaries with them into
the tunnels--not for companionship or their perky song,
but as living barometers of oxygen and toxic gas levels,
to which they were more sensitive. Today, those frogs that
tormented you in biology class--or charmed you on warm spring
evenings --may serve the same purpose. Because they breathe
through their skins and depend on water for out-of-body
reproduction, they tend to be more sensitive to both chemicals
and radiation. But we are injured, too, even if the effects
are less apparent or easily measured.
At
the very least, we should pay special attention to the fate
of those frogs and salamanders shivering our web. Those
politicians, who did much better in poli-sci class or economics
than in biology, may not realize when the strands are in
danger of falling apart.
