Shape-Shifting Frogs

On Monday, we reported on a fish that changes color to sneakily capture prey. Today we report on a frog that doesn’t change color, but changes texture—the first amphibian known to have this shape-shifting capability. Pristimantis mutabilis, or the mutable rainfrog, lives in Ecuador’s western Andean cloud forest, and is able to change texture to match its surroundings.

In 2009, scientists Katherine and Tim Krynak discovered a small, spiny frog, nearly the width of a marble, sitting on a moss-covered leaf. They had never seen this frog before and captured it, placing it in a cup with a lid before resuming their nightly search for wildlife. They nicknamed it “punk rocker” because of the thorn-like spines covering its body.

The next day, Katherine Krynak pulled the frog from the cup and set it on a smooth white sheet of plastic for Tim to photograph. She found that it wasn't spiky at all—it was smooth-skinned. The two scientists assumed that, much to her dismay, Katherine must have picked up the wrong frog.

“I then put the frog back in the cup and added some moss,” she says. “The spines came back... we simply couldn't believe our eyes, our frog changed skin texture!” Then she tried it the other way. “I put the frog back on the smooth white background. Its skin became smooth.” The two discovered that the amphibian can shift skin texture in a little more than three minutes.

“The spines and coloration help them blend into mossy habitats, making it hard for us to see them,” she says. “But whether the texture really helps them elude predators still needs to be tested.”

Their colleagues tested a related frog, Prismantis sobetes, with similar markings but about twice the size of P. mutabilis. They discovered that P. sobetes had the same trait—when they placed a spiny specimen on a sheet, its skin turned smooth. P. sobetes is the only relative that has been tested so far.

The Krynaks plan to continue surveying mutable rain frogs to document their behaviors, lifecycle, and texture shifting and to estimate their population. They hope their research will support efforts to conserve this paradigm-shifting species. The scientists are also curious about the evolution of this unique trait. Are more of their relatives able to adjust their texture? And if P. mutabilis and P. sobetes are the only species to have this capability, did it come from a common ancestor or did it evolve independently in each species?

No word on whether the scientists hope to harness this ability for their own shape-shifting super powers.

The research is published this week in Zoological Journal of the Linnean Society.

Image: Zoological Journal of the Linnean Society