At first glance, most salamanders don’t stand out: Their mottled, earth-toned skin helps them blend into the background of forests and streams around the world. But shine the right type of light at them, and they will light up like glow sticks.
That’s the finding of a new study, which reveals for the first time that most amphibians, from salamanders to frogs, have biofluorescence, a trait in which fluorescent compounds in the body absorb surrounding light and re-emit it at specific wavelengths, including red, green, and blue. Previously, swell sharks, corals, and some fish were shown to glow when the right light hit, but only a few land-dwelling animals were known to biofluoresce.
In the new study, scientists placed specimens from 32 species—including salamanders; frogs; and limbless, wormlike amphibians known as caecilians—onto a dark background and shone a blue or ultraviolet light on them. Then, they took pictures using a digital camera with a filter that captures green to yellow wavelengths. The researchers found that all of the animals were biofluorescent, they report today in Scientific Reports.
Although there were some differences, such as the intensity of the color or the body parts that glowed, they all emitted a greenish to yellow light from their skin (like the alpine newt, above). Some had glittering bones (one salamander’s finger bones flashed neon green, for example), and others had sparkling skin mucus and even urine.
This widespread occurrence suggests biofluorescence appeared early in the evolutionary history of amphibians, the researchers say. But why it appeared is another matter entirely. Although some animals use biofluorescence to find mates or communicate, scientists still aren’t exactly sure how or why amphibians glow. But, they say, it could help them locate each other under the low light of their natural environments.