In Blue Light, Most Amphibians Have a Neon-Green Glow

Researchers at St. Cloud State University in Minnesota shed light on frog and salamander bioluminescence

Glowing frog
This Cranwell's frog fluoresces green in blue light Courtesy of St. Cloud State University, Photo by Jennifer Lamb and Matthew Davis

Common newts, frogs, and salamanders may look muddy brown or leafy green, but that’s just what they want you to think. Their camouflage helps them blend in to their natural environment to hide from danger. But in the right light, these well-hidden critters start to glow.

Researchers were already aware of fluorescence in a handful of amphibians, the damp-skinned animals that can split their time between land and water. But St. Cloud State University herpetologist Jennifer Lamb and her colleague, ichthyologist Matthew Davis, began to wonder if more common species had been checked carefully for the same characteristics. Their results, published in Scienctific Reports on Thursday, shows that 32 diverse amphibian species can all glow.

“We forget to ask the same things about species that are common that we’d ask about rarer species,” Lamb tells Discover magazine’s Leslie Nemo.

Fluorescent animals don’t glow all on their own, and researchers need special filtered lenses to see them shine. The creatures rely on specific molecules that absorb surrounding light, and then re-emit that energy as a specific color of light, like neon green. But Lamb and Davis realized that previous research was only addressing half of the question, reports the New York Times’ JoAnna Kleins. When testing amphibians for fluorescence, studies had only used UV light, which causes some land animals to glow. At the depths of the ocean, blue light makes sea creatures glow, and blue light is also the primary color in amphibians’ muddy freshwater habitats.

When they realized this connection, the researchers shined blue light on a set of newts they already had in the lab. When the newts appeared fluorescent green through filtered lenses, the team set out to find other amphibians to check for the same trait. They brought their lab tools out to the field and to Chicago’s Shedd Aquarium, where they were able to look at the critically endangered hellbender salamander.

“That was a lot of fun,” Lamb tells the New York Times. “Basically a bunch of scientists running around after dark in an aquarium with a lot of bright lights and fancy goggles.”

They found that every species glows a little differently. Sometimes its spots light up, or maybe everything but the spots gleam. Other times, the critter’s bones, skin mucus, or urine lit up under blue light, even as larvae. But all of them turned green, which implies that fluorescence is an amphibian trait that appeared early in their evolution, Rodrigo Pérez Ortega writes for Science magazine.

The trait could be useful for amphibians to find each other at night without tipping off predators, the researchers say, but they’re still not sure exactly why the glowing is useful. But as the New York Times points out, the find has implications for future research. Researchers who survey disappearing populations of amphibians could make use of the trait to spot green-fluorescing salamanders in a jungle. And new florescent molecules are useful in bio-engineering, evidenced by the fact that the isolation of jellyfish’s green fluorescent protein won the Nobel Prize in Chemistry in 2008.

Moving forward, Lamb tells the Times that she plans to test the use of fluorescence in the organism she specializes in, tiger salamanders.

“I’ll be careful going forward not to put my own biases of perception on the organisms I study,” she tells Discover. “We forget to ask if other species might perceive the world in different ways.”

Get the latest stories in your inbox every weekday.