Education: Stories from the Field

mountain yellow-legged frog

A World without Frogs?

Can you imagine it? Scientists around the world—including the ones here at the Zoological Society of San Diego—are hard at work trying to prevent it.

Since the 1980s, global amphibian declines have been noted and studied. And not just mild declines; scientists have documented dramatic drops and even mass localized extinctions of entire species. In fact, scientists believe that over a third of the world’s amphibian species are threatened; since the 1980s, more than 120 species have become extinct! Many of these have taken place in Australia, Central America, South America, and the U.S.

There are a number of reasons cited for these declines, including habitat destruction, the pet trade, climate change, introduced species, pollution, and disease. One of those diseases is chytridiomycosis, an infectious disease caused by a fungus Batrachochytrium dendrobatidis, which affects amphibians’ ability to respire through the skin.

The first known record of chytrid infection in frogs was in the African clawed frog, a frog commonly sold in pet stores and used in laboratories worldwide. Today we know that many of the recent extinctions of frogs in Australia and the Americas are linked to this fungus. Dr. Allan Pessier, a San Diego Zoo veterinary pathologist and researcher, has been working with other scientists to survey and document the impact of chytrid in central Panama.

Because amphibians usually have a life cycle that includes both an aquatic and a terrestrial phase, they are susceptible to environmental effects on land and in the water. In addition, their skin is highly permeable, so they may be more sensitive to toxins within these environments. As a result, some scientists look to amphibians as indicators of the environmental health of an area, and believe that declines in populations of amphibians indicate that other animals and plants in the area will eventually be at risk as well.

Right here at home, the San Diego Zoo is contributing to the health of frog populations by maintaining a successful breeding program of some rare and endangered frog species. You can see several of them—including the Panamanian golden frog, the golden mantella, and the Bornean eared frog—on exhibit at the Zoo. Our researchers also hope to begin a captive breeding program for local mountain yellow-legged frogs (the southern population is extremely endangered, found only in Southern California's San Jacinto, San Bernadino, and San Gabriel Mountains).