New Haven, Conn. D Many frog and other amphibian species throughout the world appear to be experiencing declining populations, with several species already extinct and others showing alarming rates of deformities. No single cause has been identified. Some scientists believe habitat disturbances are to blame, although declines have occurred in relatively undisturbed areas.
Now, field experiments in the Oregon Cascade Mountains have confirmed what many scientists had suspected -- ambient levels of ultraviolet-B (UV-B) radiation from the sun can cause high rates of mortality and deformity in some species of frogs and other amphibians. The earth is shielded from UV radiation by the ozone layer, which is believed to be thinning because of the increased use of chlorofluorocarbons as refrigerants, solvents and cleaning agents.
"There has been a great deal of recent attention to the suspected increase in amphibian deformities. However, most reports have been anecdotal, and no experiment in the field under natural conditions had been performed previously," said Joseph M. Kiesecker of Yale University, who presented his findings Feb. 17 at the annual meeting of the American Association for the Advancement of Science in Philadelphia.
Kiesecker, along with Andrew R. Blaustein of Oregon State University, compared the embryos of long-toed salamanders shielded from UV-B radiation by mylar filters to unshielded embryos. They found that 95 percent of the shielded embryos hatched, compared to only 14.5 percent of the unshielded embryos. Even more striking, only 0.5 percent of the surviving shielded salamanders had deformities while 91.9 percent of the unshielded salamanders had deformities. Malformed tails, blisters and edema were the most frequent deformities.
"The recent thinning of the protective ozone layer in the upper
atmosphere has been linked to increased risks of skin cancer and cataracts
in humans as well as t
Contact: Cynthia Atwood