It’s Easy Being Green: Most Amphibians Are Biofluorescent, Study Finds

If you walk through a forest at night, you see only darkness and shadows, and perhaps the smudgy outline of trees against the sky. But if you were a salamander snuggled in the leaf litter, under the right light conditions, you might see something completely different: foliage glimmering in shades of red, and your fellow amphibians glowing in brilliant greens.

Biofluorescence—in which animals emit a fluorescent glow after absorbing high-energy wavelengths of light—is likely widespread among most, if not all, amphibians, according to a new study published in the journal Scientific Reports. Previously, only one species of salamander and three frog species were known to biofluoresce.

“I do field work, so I’m out there capturing species of amphibians, and I think, ‘huh, I wonder if this fluoresces,’” says Jennifer Y. Lamb, an assistant professor of biology at St. Cloud State University in Minnesota. She and co-author Matthew P. Davis, an assistant professor at the university, collected representatives from eight of the 10 salamander families, five families of frogs, and one family of caecelians, a type of limbless amphibian. They exposed each critter to high-energy blue light and then viewed them through a yellow filter to see if and how they glowed.

“One of the first salamanders we tested was the Eastern tiger salamander. We saw that it fluoresced really brightly, and that kind of got us hooked,” Lamb tells Mental Floss. “We started [to look] across salamander diversity, [and asked ourselves], ‘OK, how many species do we see within salamanders that biofluoresce?’ When we started to notice, ‘hey, it’s actually a lot of them!’, the question became, ‘can frogs do it?’ Then we looked at a relative of frogs, the caecelians—‘do they do it?’ And it seemed like biofluorescence in some form or fashion is present in all of these lineages.”

The various amphibians fluoresced in unique patterns depending on their skin’s coloration and markings as seen under normal white light. Some gleamed in blotches, others in stripes. A few animals' bones glowed. Lamb was surprised to see that salamanders’ bellies, which were usually red or orange under white light, glowed brighter than their backs after exposure to blue light.

“A lot of these newts have evolved what we call aposematic coloration, or warning colors. When they’re threatened by a predator, they’ll basically contort their bodies to show off their bellies as a warning,” Lamb says. “So it begs the question, if these bellies are also biofluorescent, then maybe some of their predators can visualize biofluorescence.”

The researchers intend their study to be a roadmap for further study into the fascinating ability. “Now that we know that this phenomenon exists across amphibians, there’s all kinds of interesting applications that future researchers may head towards,” Davis tells Mental Floss. For example, no one yet knows what kind of mechanisms allow amphibians to biofluoresce: In some groups it might be a color-based molecule or compound; in others, maybe something in their mucus.

Scientists also don’t know exactly how different amphibians might visualize their own biofluorescence. Salamanders, frogs, and caecelians have rod cells in their eyes that are sensitive to green light, suggesting that they may have evolved green biofluorescence and the ability to see it at the same time, though further research is needed on that front.

“We have to be careful about not falling into the trap of only perceiving the world through our own eyes,” Lamb says. “Human vision is set to a particular set of wavelengths, and that’s not the case across all animal diversity. And that may not be the case in terms of these amphibians.”

Finally, researchers are debating what purpose biofluorescence serves. In other animals, scientists have suggested it could play a role in communication, camouflage, or choosing a mate. Amphibians might use biofluorescence to locate each other in dense leaf litter.

“We’re hoping this study stimulates researchers to start looking at biofluorescence more broadly across the various different kinds of amphibian lineages that they may work on, so we can fill in the gaps in knowledge,” Davis says.

“There’s still a lot to learn about animal groups that we think we know,” he adds. “There’s still lots of interesting things out there to find that can help us rethink their life history and biology, and that may point us in new exploratory directions.”