Fire salamanders, one of Europe's most recognizable amphibians, turn out to hide an ability scientists had never documented: their skin fluoresces green and cyan under ultraviolet light, most visibly on the yellow underside and along their flanks.
Researchers traced the glow to glands in the salamander's skin and the toxic secretions those glands release — secretions that remain fluorescent for more than 24 hours after leaving the animal's body. "It is fascinating that such a well-studied species still harbors unknown phenomena like this," said Bernat Burriel, a researcher at the Museum of Natural Sciences in Barcelona and the study's first author. "It reminds us that even the most familiar organisms can hide secrets that are only revealed when they are observed with new tools."
The effect is known as biofluorescence, in which compounds absorb ultraviolet light — invisible to humans — and re-emit it as visible color; it requires an outside light source, unlike the self-generated glow of fireflies. Scientists once assumed the trait was almost exclusive to marine life, but it has turned up in a growing list of land animals, including reptiles and birds.
Why fire salamanders glow remains unclear. One theory holds that the fluorescence helps them recognize each other or assess potential mates in dark, dense forest habitats, since full moonlight carries more ultraviolet and violet wavelengths than daylight. Another holds that it sharpens their existing yellow-and-black warning coloration, making their toxicity more obvious to predators. "Fluorescence meets several criteria that suggest a communicative function," said Martin Kaltenpoth of the Max Planck Institute for Chemical Ecology, a co-author of the study. "It could help salamanders detect each other in nocturnal or particularly dense environments, or act as an additional defense signal."
Researchers have studied salamander skin chemistry for decades, which makes the discovery a surprise. "The presence of this fluorescent compound was surprising because salamander skin secretions have been studied chemically for decades, and we were unaware of any published reports on fluorescence," said co-author Andrés Brunetti. The species is already listed as vulnerable by the IUCN, adding urgency to understanding behaviors that habitat loss could disrupt before scientists fully decode them.