New research suggests that amphibians -- already the most threatened vertebrate group in the world -- are even more likely to contract a disease because of stress.

Researchers at Duquesne University found that frogs, salamanders and their kin, which are seen as indicators of environmental conditions, are experiencing extreme population declines linked to an often-deadly fungal infection from Bactrachochytrium dendrobatidis. The recent findings bring bad news for amphibians -- and any fan of biodiversity -- and challenge humans to find ways to lower their stress levels.

The research supports the hypothesis that environmental stressors increase salamanders' susceptibility to infection, based on chronic exposure to corticosterone, a stress hormone.

For the study, researcher Shelby Boord and her colleagues treated red-legged salamanders with either the hormone or oil for nine days before exposing them to the fungal pathogen. Using molecular techniques, she measured infection at baseline, day 10 and day 17. Boord monitored the subjects for disease symptoms for 30 days after exposure.

All of the exposed animals became infected. However, those treated with the hormone had a greater abundance of harmful pathogens than the control group.

Because of this new evidence relating stress hormones with infection rates, the research provides a call to minimize amphibians' exposure to environmental stressors to bolster their disease resistance and allow them to survive in a rapidly changing world.

The U.S. Fish & Wildlife Service notes the decline in amphibians may be more severe and widespread than previously realized. With more than 41 percent of all amphibians at risk of extinction, the International Union for the Conservation of Nature calls them the most threatened vertebrate group.

The findings were presented at the March 3 Undergraduate Research at the Capitol-Pennsylvania event.