These Captive-Bred Frogs Are Facing Predators and the Chytrid Fungus to Make It in the Wild

Scientists in Panama release 500 harlequin frogs, some wearing transmitters, in a first attempt to reintroduce the endangered species

Once common along highland streams in Costa Rica and western Panama, the variable harlequin frog, Atelopus varius, is now endangered throughout its range, thanks in large part to a disease caused by the amphibian chytrid fungus. (Brian Gratwicke, Smithsonian Conservation Biology Institute)
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Exploring the dense montane forest of western Panama, you’re likely to spy swooping harpy eagles, long-tailed quetzals, sleepy sloths, ululating howler monkeys and dozens of brilliant butterflies. With all the action above the forest floor, you might never consider the tinier wildlife scuttling about your feet. Some of the most remarkable organisms in the forest are frogs and toads (anurans), 170 separate species of which call Panama their home. One of the most striking types of anuran, the variable harlequin frog, is on the brink of extinction. Smithsonian conservationists are looking to prevent that.

In 2006, the Smithsonian Conservation Biology Institute, based in Washington, D.C., joined forces with the Smithsonian Tropical Research Institute in Panama and three major U.S. zoos—Cheyenne Mountain Zoo, Houston Zoo and Zoo New England—to confront head-on the decline of amphibian populations in Panama. Ever since then, the Panama Amphibian Research and Conservation (PARC) Project has been working to keep the forests hopping with as many exotic frogs and toads as can be saved.

The critically endangered variable harlequin frog, also known as the clown frog, is a top priority for PARC. Harlequin frogs are “specialized members of the toad family,” says Smithsonian conservation biologist Brian Gratwicke, that “have more colorful skin than most frogs, which is where they get their name.” Arresting color combinations like hot pink on jet black suggest to predators that these frogs are not to be trifled with—their skin is infused with a deadly neurotoxin.

But while poison might be able to deter would-be predators, Gratwicke says these frogs have a more pressing issue to worry about. “They are very sensitive to the amphibian chytrid fungus,” he says, referring to an aggressive infectious disease that’s been decimating frog and toad populations all over the world in recent years. Some scientists theorize that global climate change could be facilitating the spread of the disease; as cloud cover from excess evaporation makes days in the forest cooler and nights warmer, the pathogen has a more stable environment in which to thrive and propagate.

Given the danger presented by this disease in the wild, the safest strategy for conservationists has been to breed variable harlequin frogs in captivity. Before too long, though, the creatures will need to be reintroduced to their natural habitat if they’re to maintain their place in the forest ecosystem. On January 17, PARC researchers took a key first step towards achieving this goal, releasing a test group of 500 specimens into the Panamanian forest. They will be tracking the group as best they can in the coming weeks.

Prior to release, each of this large batch of frogs was tagged as an aid to human observers looking to monitor their progress. “They have unique markings,” says Gratwicke. “We implanted a colored fluorescent dye beneath the skin in one of the hands or feet.” This dye will reveal itself when scientists shine UV light on it, allowing them to keep track of which frogs are theirs and which are wild.

One of 30 radio transmitter-equipped frogs included in the larger group of 500. (Brian Gratwicke, SCBI)

The monitoring of the newly released frogs will also involve a completely different type of technology: radio. “We’re doing a radio tracking study with about 30 of the 500 frogs,” Gratwicke says, “to understand how widely they disperse in the area.” Methodologically, this is simple enough: “We tie a 0.3-gram radio transmitter to the frog.” But, he adds, these transmitters are “very expensive”—hence the modest size of the radio-equipped subgroup—and their battery life is 21 days, setting constraints on the project. This portion of the team’s field work will be coming to an end in one week’s time.

At the start of the trial re-release, Gratwicke wasn’t sure exactly what to expect. Introducing captive animals to the wild is always a dicey proposition, even without the lingering threat of disease to worry about. These frogs, he says, are used to “24-hour room service”—crickets hand-delivered every day by their human caretakers. But even if this initial experiment isn’t a total triumph, Gratwicke is sure that the results will be of value to the PARC conservation team as they plan their next steps on the road to full reintroduction.

“Release trials may or may not succeed,” Gratwicke says, “but the lessons we learn will help us to understand the challenges faced by a frog as it transitions from captivity into the wild.”

About Ryan P. Smith
Ryan P. Smith

Ryan recently graduated from Stanford University with a degree in Science, Technology and Society. His avocations include moviegoing and crossword puzzle construction.

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