Wild Frogs' Special Delivery

July 08, 1995|By Frank D. Roylance | Frank D. Roylance,Sun Staff Writer

It's not Niagara Falls, but the honeymoon accommodations at the National Aquarium in Baltimore suit the finicky giant leaf tree frogs well enough.

The foggy, leaf-shrouded chamber built by curators at the aquarium has aroused the peach-sized tropical frogs enough to produce baby frogs. It's believed to be the first time the species has done that in captivity in the world.

It wasn't easy. For a long time, nobody was sure what the females looked like, and it took the aquarium 12 years to acquire one. Then scientists had to figure what turns the frogs on. Artificial rain didn't do it, even though the wild frogs breed only in the rainy season.

"It's trial and error," said rain forest curator Jack Cover. "We look at what's going in the wild and try to re-create it. It feels really good when it works."

Aquarium scientists have previously learned to breed 22 species of the smaller, more colorful poison dart frogs, some for the first time in this country. Their success has produced both captive-bred animals and frog-handling expertise for other institutions, reducing the pressure to collect wild frogs from the dwindling rain forests.

With the aquarium's latest success, Mr. Cover said, "we should be able to supply all the other zoos and aquariums in the country with this particular species."

"They are wonderful exhibit animals," said Sandy Barnett, the aquarium's senior herpetologist. The National Aquarium has four adult males on display, nine more males and one female in reserve. The newborns added 23 young of undetermined sex.

It's easy to miss the bright green frogs in the rain forest exhibit. They sit so still in the greenery that they are easily mistaken for leaves.

Known to science as Phyllomedusa bicolor, the frogs are found in the Amazon and Orinoco river basins of South America, where they live high in the forest canopy. They have evolved a slow, deliberate walking motion, an opposable thumb and suction-cup fingers.

Nocturnal feeders, the frogs spend their days sleeping. They can live up to 35 years, eating a diet of mineral-enriched live crickets.

To protect themselves from excessive drying, the frogs rub their heads and backs with a waxy substance produced by a gland. The shiny wax makes the frogs look like bell peppers. Indians living near the Peru-Brazil border use the frogs' wax to make "hunter magic," a potion used to sharpen their senses for hunts. Biochemists have discovered a rich lode of amino acids in the wax that could one day lead to a new class of psychoactive drugs.

Dr. William E. Duellman is professor and curator of herpetology at the University of Kansas and an expert on the frogs. He said the aquarium's success will be important to scientists at the National Institutes of Health who are studying the frog wax. "If you can get a steady breeding colony of these things, people . . . could really go to work on this biochemical."

The aquarium has exhibited giant leaf tree frogs for 12 years, but until past year had never been able to obtain a female for breeding. "They are difficult animals to collect," and they have become available only twice in the past 5 1/2 years, Ms. Barnett said. Females are especially elusive. The males are more common and forage closer to the ground, where they are more easily caught.

It's also difficult to distinguish between the sexes. Last fall, when an importer offered a shipment from Suriname, "we asked for the 10 biggest frogs," Ms. Barnett said. Females tend to be larger, and the aquarium hoped to get lucky.

Examining the 10 new frogs, Mr. Cover said, "we found one frog that was bigger." It also lacked a tiny black pad at the base of its thumb, a feature thought to be unique to males. It was female.

The next challenge was to create an environment that mimicked the frogs' forest canopy home, and the rainy season in which they breed. A 5-foot-high glass chamber filled with branches and leafy plants worked well enough, but reproducing the jungle weather proved a bit trickier. "First we had to put her into a dry season," Ms. Barnett said. That meant lowering the humidity and water level in the chamber without drying out the plants or the frogs.

When it was time for the rainy season, she raised the water level in the chamber and sprayed regularly with an artificial rain.

The rain had spurred poison dart frogs to reproduce, but the giant leaf tree frogs weren't buying it.

The scientists went back to their books and discovered one observer who noted that the wild tree frogs seemed to spawn more on foggy nights. So, on April 21, they replaced the "rain" with an ultrasonic humidifier that produced a "pea-soup fog" in the frogs' honeymoon suite.

"One night of fog did it," Ms. Barnett said. By morning, the female had laid 1,947 BB-sized eggs on a leaf. After spawning, the frogs curled the leaf around the eggs like a cigar.

It turns out the accommodations weren't perfect. The leaf proved too weak to support the breeding frogs properly. It tipped in a way that kept most eggs from being fertilized.

But on May 1, those that were fertile began hatching, and the new tadpoles flipped themselves into the water at the bottom of the cage. Twenty-three underwent metamorphosis and emerged from the water as frogs that are now dime-sized and baby blue.

Next time, the leaves will be better supported, Mr. Cover said. If it works, "we will have almost more frogs than we can handle."

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