Froggy goes a-courtin' Reproduction: When Madagascar tomato frogs are pampered with just the right conditions, one thing leads to another in the terrarium and pretty soon there's a tadpole explosion.

Anthony Wisnieski and Erik Anderson think they've figured out how to put a frog in a romantic mood.

They have plenty of proof to show for it: Their rare Madagascar tomato frogs went a-courtin' at the Baltimore Zoo, and now they have about 4,000 baby tomato frogs and tadpoles.


Wisnieski, the zoo's curator of amphibians, and Anderson, the amphibian keeper, say they have developed an environmental setting -- the right blend of humidity, air temperatures and lighting -- that induces the frogs to mate.

"We really did our homework with this, and I think it paid off," Wisnieski said, showing off the progeny swimming in back-room storage tanks at the zoo Reptile House.


The zoo has periodically displayed its 14 tomato frogs at the Reptile House in Druid Hill Park since 1994, when they were donated by scientists from the University of California at Berkeley.

They make for quite an attraction.

Named for their bright color, the tomato frogs (Dyscophus antongilli) can grow to the size of a plump, ripe tomato when they are fed a steady diet of newborn rodents and insects.

Endangered species

But Madagascar is the only place where the tomato frog lives in the wild, and deforestation of its tropical rain forest habitat, coupled with over-collection by poachers, has earned the bright orange amphibian a place on the Endangered Species List.

"They're beautiful, but they're getting harder and harder to find," Wisnieski said.

So in May, Wisnieski and Anderson put five tomato frogs in a specially equipped terrarium in a back room of the Reptile House, where they shared storage space with vipers from South America and newts from southern China.

There, the two animal researchers set about to find the amphibious equivalent of a candlelight dinner for two.


First, they decreased the depth of the water pools.

Then they reduced humidity levels, cut back on lighting and dropped the temperatures from 75 degrees to about 70.

Mating season

Finally, they gradually increased the humidity, temperature, amount of light and water depth -- in effect duplicating the arrival of the frogs' mating season.

The frogs just couldn't resist. They began making their mating calls and mating, and laying the thousands of eggs that have grown into tomato frog tadpoles and baby frogs and have been swimming in the zoo's terrariums for the past few weeks.

"They just responded beautifully," says an enthusiastic Wisnieski.


Many of the youngsters will be donated to other zoos and institutions, he said.

The tomato frog has been bred successfully in captivity before. But previous breeding programs at Berkeley and other zoos have involved giving the frogs hormones, which stimulate reproductive glands.

A first for the zoo

This experiment makes the Baltimore Zoo the first zoo in North America to breed the species without hormones, frog experts say.

"What it means is, we're getting a better understanding of what the animal really needs for its reproductive cycle," said Dr. Dale Denardo, an endocrinologist at Berkeley and expert on tomato frogs and other amphibians.

Denardo said that hormones will be used in many frog breeding efforts. But the fact that it can be done without hormones is heartening, he said.


"It makes things a lot simpler if you don't have to use hormones; it's nice to be able to skip that step," he said.

Wisnieski said the tomato frog experiment is intended to highlight the need to save the frog -- as well as the rain forest that is its home.

"What we have in the tomato frog is a bright, shiny, showy frog," Wisnieski said. "We thought it would help us get our conservation message across to the public."

Pub Date: 8/12/97