Fire salamanders may scare away predators with fluorescent glowing goo
Despite being in the scientific spotlight for centuries, the fire salamander’s biofluorescence was overlooked until now.
In antiquity, many thought salamanders were fire-proof. The legend, which likely originated from the amphibians’ penchant for living in firewood, inspired the common name of the fire salamander, a poisonous species native to Europe that is aflame in bright yellow and black splotches.
While they are not flame-resistant, new research reveals these fiery salamanders do glow. A team of scientists recently inspected several fire salamanders under an ultraviolet light and discovered that the amphibians’ bellies and sides lit up in a constellation of bluish-green dots—and their bodies secreted a glowing goo. In a paper published today in the journal Royal Society Open Science, the scientists propose these sparkling speckles may serve as a glowing display to scare predators or attract mates on the dark forest floor.
The fire salamander joins a growing group of amphibians that display biofluorescence, or the ability to absorb light at one wavelength and emit it at a different wavelength, often in shades of green, orange, or red. “We are in a thrilling period of discovery in terms of biofluorescence in amphibians and other tetrapods,” says
Jennifer Lamb, a herpetologist at St. Cloud State University in Minnesota who was not involved in the paper. She adds that discoveries like this “help fill some of the gaps in our understanding, both in terms of what species fluoresce and in terms of the mechanisms likely responsible for that fluorescence.”
Neon dots and glowing goo
Biofluorescence was once thought to be primarily restricted to marine invertebrates and arthropods like scorpions. But over the last two decades, new science has shed light on several groups of vertebrate animals that also reflect light at different wavelengths, including pink squirrels, platypuses, and sharks. In 2020, Lamband a colleague published the first evidence of biofluorescence in salamanders and other amphibians.
The uptick in biofluorescent amphibians inspired Bernat Burriel-Carranza, an evolutionary biologist at the Natural Sciences Museum of Barcelona and the lead author of the new study, to bring an ultraviolet (UV) flashlight with him into the field. Few of the critters he encountered had a hidden glow. But one rainy night while collecting in Spain, he tested a fire salamander that was crossing a road. “When we shone the UV light onto the animal, we could not believe how bright the fluorescence was along its flanks,” he recalls.
Burriel-Carranza was particularly surprised because fire salamanders have been in the scientific spotlight since Swedish naturalist and pioneering taxonomist Carl Linnaeus named the species in 1758. Over the centuries, researchers have studied many aspects of the salamander’s biology. Fire salamanders are also a textbook example of aposematism, a defensive strategy where toxic animals use eye-catching colors to deter prospective predators.
To examine this well-known species in a different light (literally), the team found several fire salamanders in forests in Spain and Germany. They photographed the amphibians under UV light and swabbed their skin to collect the poisonous secretions.
The scientists discovered bright teal speckles on 10 of the 12 specimens they encountered in Spain’s Catalonia Territory (fluorescence was rarer among the fire salamander subspecies surveyed in Germany, possibly due to different environmental conditions). The fluorescence peaked along the amphibians’ sides, throat, and stomach and was largely concentrated in yellow splotches on the salamanders’ skin.
Interestingly, even the salamanders that lacked these bright spots produced glowing goo—every secretion the team collected, including those from the German subspecies of fire salamander, exhibited fluorescence. The secretions continued to shine under the UV light for at least 24 hours.
This glowing ooze led the team to hypothesize that the salamander’s fluorescence was linked to the glands that produce the secretions. The team dissected two fire salamander specimens that were pickled in a museum collection. They then analyzed slices of the salamander tissue under a microscope. The team found fluorescent compounds in the salamander’s glands as well as its bloodstream, providing evidence these glowing compounds are transported throughout the amphibian’s entire body.
According to Burriel-Carranza, a similar setup is seen in only a couple other amphibians. Some treefrogs produce and circulate fluorescent compounds through their lymphatic systems, which light the frogs’ translucent bodies like lanterns. And some woodland salamanders in the group Plethodon exhibit similar speckles, although these are produced by different glands than those in fire salamanders.
A sparkling sign
The team suspects that fire salamanders’ fluorescence serves an ecological purpose. Burriel-Carranza notes that other amphibians, and potential predators, can see the wavelengths emitted by these bright spots. As a result, the salamander’s glowing secretions could serve as a flashing warning to predators that these amphibians are toxic.
The team also hypothesizes that biofluorescence may also help male salamanders, which are covered in more yellow splotches than their darker female counterparts, stand out during mating season. Males are not afraid to flash their lights—these salamanders often raise up to display their chests and throats, where fluorescence is most intense. Like a neon sign, this fluorescent display “should be visible to other salamanders and highlights them in the dark forest floor,” Burriel-Carranza says.
The fire salamander’s fluorescence should also attract other scientists to examine the fluorescence of even well-known species, says Courtney Whitcher, an independent researcher who studies biofluorescence in treefrogs but was not part of the study. “Discoveries are inherently a product of what we look for,” Whitcher says. “Increased documentation of biofluorescence in amphibians will drive scientists to begin testing and documenting this trait more often.”
Like Burriel-Carranza, other biologists would be wise to have a UV flashlight handy when they go looking for amphibians.
