It was 25 years ago when the alarm bells sounded about the dangers of thinning ozone from aerosols and propellants, fueling fears of increasing incidence of human skin cancer. It took another decade for a link to be proposed between declining frog and salamander populations around the globe and increases in ultraviolet (UV) radiation. New research by SFU Biologist Wendy Palen published May 17 online in the Proceedings of the National Academy of Science finds that amphibian species thought to be harmed by UV radiation in the U.S. Pacific Northwest appear to be far less susceptible than previously thought. (Water clarity, maternal behavior, and physiology combine to eliminate UV radiation risk to amphibians in a montane landscape)

But Palen cautions that their findings should not be misinterpreted as contesting the hundreds of studies demonstrating the harmful effects of UV radiation for many organisms including humans. Instead she says, “By understanding where and when it is harmful we have a better chance of predicting the consequences of global changes for natural ecosystems. In the case of frog and salamander populations headed towards extinction around the globe, the need to understand which threats to natural ecosystems are most important has never been more urgent.”

While many species of amphibian have been tested for their sensitivity to UV radiation, tests were often conducted in highly controlled laboratory environments or in just one or two natural sites. In some cases, species were extremely sensitive to UV radiation, with especially high mortality in their aquatic stages (eggs and larvae).

Working with colleagues at the University of Washington in Seattle, Palen has found that these physiological tests of species sensitivity are poor indicators of overall vulnerability to UV radiation in the wild.

Palen is an ecologist and she holds a Canada Research Chair in Aquatic Conservation at SFU. Coauthor Daniel Schindler is H. Mason Keeler Professor at the School of Aquatic and Fishery Sciences at the University of Washington. They conducted experiments and surveys across the full range of environments used by two different amphibians that occur in the mountains of the Pacific Northwest.

The authors intentionally looked at both the most sensitive species that has been tested from this region (long-toed salamanders, Ambystoma macrodactylum) and the least sensitive (Cascades frogs, Rana cascadae) to understand the range of possible effects. Palen and Schindler found that fewer than 2% of the embryos of each species are exposed to lethal levels of UV radiation in mountain lakes and ponds of the Olympic National Park.

Key to their study is the observation that some species that are sensitive at a physiological level exhibit behaviors that limit their exposure to harmful UV radiation in their natural environment. They found that the combination of the clarity of the water at amphibian breeding sites and where female frogs and salamanders choose to lay their eggs has a large effect on their exposure to UV, neither of which is captured by simple laboratory experiments.

“When these simple tests of species physiology are interpreted outside of the animal’s natural environment, we can easily come to the wrong conclusion” says Palen.

“If we had taken the results from a single experiment conducted in the most UV exposed breeding site in our study and assumed that those conditions were present everywhere the species breeds, we would say that almost 100% of the embryos of one of these species are exposed to lethal levels of UV”, she says, emphasizing that variation in the environment is what matters in this case.

A key lesson says Palen, is that scientists have to constantly ask whether the conclusions they reach are dependent on the methods used. Rather than being counterproductive, scientists need to look backwards to refine the priorities for research and conservation.