Frog-chasing youth nabs one with six legs Genetic error believed to cause mutation in common green variety

September 04, 1996|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

Life can go two ways when you're born with six legs.

You can become a snack for snakes, or some biologist can plop you into a glass bowl and feed you to the news media.

It was the second fate that befell a little mutant green frog from Riverside, in Harford County, over the holiday weekend. She now resides in a walk-in cooler at Towson State University, the ward of TSU herpetologist Don C. Forester.

"She looks very healthy," he said yesterday as the frog -- no bigger than a half-dollar -- hopped up his arm with all four hind legs in motion for the camera.

"But she is probably too cumbersome, too awkward" to survive for long in the wild, he said. "If it were Carl Lewis with two extra legs hanging off him, he wouldn't jump as far as he jumps."

Known to science as Rana clamitans, the green frog is common in Maryland, where it enlivens wetland areas with a call -- "glunk" -- that sounds like a loose banjo string.

It has so far escaped whatever is causing sharp declines in many amphibian populations around the world.

"They're doing fine. They can live in so many habitats, there's no indication at all of a decline in green frogs," said Forester, 53. He specializes in the study of the reproductive biology and courtship behaviors of frogs and toads.

The little mutant was found by Alex Polyak, 11, of Riverside, a sixth-grader at Saint Joan of Arc School in Aberdeen.

"I found it in the woods behind my house," Alex said. Wet weather creates little ponds in the woods, and he and his friend Ryan Shumaker, 9, were out there Saturday afternoon looking for frogs, turtles, snakes and newts.

"I was just catching them and letting them go," he said. "I found four [frogs] in all, and this was the second one that I found. I didn't realize it had six legs at first. After I saw this one, I looked at the other ones, but they were normal."

The frog is a youngster. Adults grow to the size of a peach.

Alex thought the mutation might have been the result of some sort of sewage pollution. But his father, Steve Polyak, doesn't believe the woods are tainted.

"If I thought that, he wouldn't be down there," he said. "I believe those kinds of things can occur in nature from time to time."

Forester agrees. Such mutations could be caused by chemical toxins or ultraviolet radiation. But this one is likely due to a natural genetic error.

Sometimes the genetic code is scrambled during reproductive cell division, and the error is passed along in the genes of the bTC offspring. Other times, the error occurs as the code is being copied for the production of key proteins or enzymes in the developing embryo.

In this case, Forester said, it was probably an error in a portion of the genetic code that controls leg development. The mutation is called hexapodia, meaning six feet.

This frog appears to have two healthy, normal legs. The extras emerge from between the first two, and appear slightly thinner. When the frog is at rest, both extra legs lie beneath her left leg. And when she hops, they move -- awkwardly -- with the first set.

"I've seen photographs of octopodia [eight legs] and hexapodia in frogs before, but it's got to be very uncommon. I've never seen it in a live frog," Forester said, "and I've spent most of my life studying frogs."

It's not the only mutation in local frogdom. Forester said there's a pond in Baltimore County that produces albino frogs.

"Ten to 15 percent of the frogs are white," he said. "Or at least the tadpoles are white. I've raised several to [adult] frogs, but in the wild they are wiped out by predators or collected by collectors."

If Alex Polyak's six-legged frog survives and grows, Forester may attempt to stimulate her egg production with hormones, then fertilize the eggs with sperm from a normal male. If any offspring have six legs, it would mean the defect is encoded in her genes.

That might have commercial importance, he joked, if French restaurants served green frogs' legs. But alas, they have no commercial value.

For now, the hexapodic amphibian will remain a curiosity in the TSU cooler, destined ultimately for formaldehyde.

Its neighbors in the cooler share froggy loneliness. They are the last mountain chorus frog tadpoles known to live in Maryland.

Forester rescued them as eggs from a roadside ditch in Garrett County not long before the ditch was scoured by a storm. The last 18 adults were washed away.

"I'll metamorphose these, take them back and release them," he said. But the species' future in Maryland remains imperiled.

Pub Date: 9/04/96

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