Endangered frogs refrigerated to spur breeding

In an effort to encourage breeding in a critically endangered frog, scientists at the San Diego Zoo’s Institute for Conservation Research have placed 24 mountain yellow-legged frogs into refrigerators.

“The cold temperatures mimic high-elevation winter conditions that cause the frogs to hibernate. Typically, mountain yellow-legged frogs display mating behaviors after emerging from hibernation,” the zoo explained in a news statement yesterday.


U.S. Geological Survey scientists found this adult mountain yellow-legged frog last year in a rediscovered population of the endangered frog in the San Jacinto Wilderness, San Bernardino National Forest, California. This re-discovery–along with the San Diego Zoo’s first successful breeding of the frog in captivity, and successful efforts by California Department of Fish and Game to restore frog habitat–renews hope of survival for this Southern California amphibian, USGS said.

Photo by Adam Backlin, U.S. Geological Survey

This is the first time the mountain yellow-legged frog has been put into a refrigerated unit to induce breeding. In 2009 the San Diego Zoo was the first to successfully breed the mountain yellow-legged frog in captivity after a slight chilling of their water, the zoo said.

“We hope that by simulating the cold of the mountains where this critically endangered frog has been found, the San Diego Zoo will be able to increase the mountain yellow-legged frog population,” said Jeff Lemm, a research coordinator for the San Diego Zoo. “The tadpoles we raise will be reintroduced into remote mountainous areas of Southern California where these frogs were found historically.”

In their native habitat, the female mountain yellow-legged frog lays eggs as soon as the snow begins to melt. A female mountain yellow-legged frog can lay up to 200 eggs that hatch into tadpoles three weeks later, the zoo said.


Jeff Lemm, a research coordinator with the San Diego Zoo’s Institute for Conservation Research, takes a sample of the mountain yellow-legged frog’s chilled water. The critically endangered frogs were put into a special refrigeration unit so they would hibernate. When the frogs emerge from the cold in April, scientists hope they will produce thousands of fertilized eggs. This is the first time scientists have chilled the mountain yellow-legged frog in an effort to induce breeding.

Photo by Ken Bohn, San Diego Zoo

“The frogs at the San Diego Zoo’s Institute for Conservation Research were put into the refrigerated units, which are beverage coolers being used as hibernacula, on January 1, 2010. After the frogs have hibernated for a few months in 40-degree temperature, San Diego Zoo scientists will begin to raise the temperature a degree a day to slowly warm them back up. Scientists expect to move the frogs to an area of the lab for breeding at the beginning of April,” the zoo said.

There are about 200 of the federally endangered mountain yellow-legged adult frogs remaining in the San Gabriel, San Bernardino and the San Jacinto mountains of Southern California, said Adam Backlin, an ecologist for the U.S. Geological Survey (USGS). Sixty-one more live at the San Diego Zoos Institute for Conservation Research. The goal of the breeding program at the Institute for Conservation Research is to return frogs to their native habitat.


While assessing suitable sites in southern California for reintroducing endangered southern mountain yellow-legged frogs, USGS scientists rediscovered a population in the San Jacinto Wilderness, 50 years since this frog was last seen there.

Photo by Liz Gallegos, U.S. Geological Survey

“Globally, amphibians are on the decline because of habitat loss, nonnative predators, effects of climate change and the spread of a deadly pathogen called the chytrid fungus. The mountain yellow-legged frog is one of three frogs or toads on the federal Endangered Species List in Southern California,” San Diego Zoo said.

The breeding at the San Diego Zoo’s Institute for Conservation Research is a part of a collaborative effort to save the species by organizations including USGS, California Department of Transportation, U.S. Fish and Wildlife Service, U.S. Forest Service, University of California, California Department of Fish and Game, and the Fresno Chaffee Zoo.

The Zoo’s breeding program, in conjunction with its partners, began in 2006 after a forest service biologist with the San Jacinto Ranger District discovered pools where the frogs had been living that were drying up. A USGS team rescued 82 tadpoles, which were taken to the San Diego Zoo’s Institute for Conservation Research, the zoo said.


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