Very rare twist of DNA takes away yellow pigment

Kevin Lollar
December 20, 2006

Blue, Lord I'm blue,
Blues raining down on me;
I've got to change my way of living,
Because the blues is all I see

— Dickie Betts

A green treefrog recently discovered and captured at Corkscrew Swamp Sanctuary in Collier County is an amphibian of a different color — blue.

The extremely rare blue green treefrog was found the weekend before Thanksgiving and has been an object of fascination for sanctuary staff and photographers.

"When I first saw it, I thought it was just a mood-ring frog, feeling kind of blue," wildlife photographer Rod Wiley said. "When I was shooting him, there was an ivory-billed woodpecker behind me, and I told the bird, 'Later: I'm busy.' "

Wiley was, of course, kidding about the ivory-billed woodpecker, which has been considered extinct for 50 years, though unconfirmed sightings have recently been reported in North Florida and Arkansas.

His point was that, while ivory-billed woodpeckers might or might not be extinct, this frog, which is startling in its blueness, might be unique.

> what homework I've done — talking to colleagues and going online — nobody else has encountered one," said Mike Knight, a sanctuary resource manager and University of Memphis doctoral candidate. "One of our volunteers saw it near the lettuce lake and alerted me that it might be an exotic frog from Southeast Asia.

"As soon as I saw the photograph, I said, 'Yeah,' and went running out there."

In scientific terms, the blue frog is axanthic, which means it lacks yellow pigment.

Green treefrogs produce a layer of yellow pigment and a layer of blue pigment, and the two combine to make green.

Something happened genetically to this frog: The genes that produce yellow are absent, and the genes that produce blue — that would be the blue genes — are present, so the frog is normal in every way except color.

"Occasionally, you get a green treefrog lacking blue, and it's all yellow; or you get one lacking all pigment, and it's albino," Knight said. "This one is more rare than an albino."

Not knowing the blue frog's genetic makeup, Knight doesn't know whether it will produce blue tadpoles that would grow up to be blue frogs.

To do so, the blue frog, which is probably a female, might need to mate with a blue male; or it might need to mate with a normal green treefrog to pass on its own genetic makeup, then the blue female would have to mate with one of her resulting offspring — a very long shot considering the extremely low survival rate for green treefrogs and the long odds of the blue frog actually meeting up with one of her offspring.

One thing is certain: Blue is not a good color for a green treefrog: The species' No. 1 defense is camouflage.

In a world without predators, being blue would not be an issue — it would be what scientists call a neutral trait, neither beneficial nor harmful.

But the frog's world is full of predators, so the axanthic gene is a maladaptive trait — it's bad for the animal.

"It's a miracle she's survived," sanctuary manager Ed Carlson said. "These frogs survive by being green and getting on something green. You can see that thing a mile away. So, what's she been doing?"

Possibly just hiding well, Knight said, or being lucky.

Certainly, some predators can't distinguish colors: To them, a blue frog would simply blend in with the vegetation.

"But there are enough predators that see in color," Knight said. "This guy should have been picked off."

Unlike some non- camouflaged amphibians, such as poison arrow frogs, green treefrogs don't produce a toxin to discourage predators.

"No, they're yummy," Carlson said. "Everybody eats them, herons, egrets, snakes, everybody."

Somehow the frog survived and now lives in a terrarium, eating crickets and being blue, until Corkscrew officials decide what to do with their rare find — options include release.

"We're going take our time deciding," Carlson said.