More mammals are fluorescent under ultraviolet light than previously thought, according to a study published last week in the journal Royal Society Open Science. By examining museum specimens, researchers documented the glowing property across 125 mammal species.
The team remains unsure whether the ability to fluoresce, or glow under ultraviolet radiation, serves an evolutionary purpose, but the wide-ranging results are a step toward figuring that out.
Fluorescence has been documented across a range of animals, including some corals, insects, spiders, fish, amphibians, reptiles and birds. But previously, scientists had detected the property in only a limited number of mammal species, the study authors write.
“These results should catalyze some interesting behavioral research on nocturnal mammals,” Michael Lee, an evolutionary biologist at Flinders University in Australia who did not contribute to the findings, tells Newsweek’s Jess Thomson.
Fluorescent organisms contain chemicals that absorb short-wavelength ultraviolet light—which is undetectable to human eyes—and emit longer wavelength, visible light that appears as a colorful glow. Such chemicals have been found in animals’ bones, teeth, claws, fur, feathers and skin.
Humans, for example, have fluorescent teeth, like all mammals do. In 1911, researchers reported fluorescence in European rabbits, marking the first documented case of the glowing ability in a non-human mammal, per the Guardian. Recently, a 2020 study found that platypuses’ bodies glow blue-green under UV light. Following that discovery, Travouillon began to wonder what other creatures might fluoresce, unbeknownst to humans.
In follow-up research, he and others found that a marsupial known as a bilby, the quills of hedgehogs and porcupines, a wombat species and other mammals glowed in the dark, the New York Times’ Cara Giaimo wrote in 2020. These findings, in turn, formed the basis for the new and more expansive study.
This time, the researchers looked at preserved and frozen mammal specimens from the Western Australian Museum collection, frozen platypus and Tasmanian devil specimens from the Tasmanian Museum and Art Gallery and koalas and echidnas from the Australian city of Yanchep. In all, they examined 146 specimens representing 125 mammal species from 79 different families.
All the species in the study exhibited fluorescence. Areas of pale and white fur on the platypus, koala, bilby and Tasmanian devil glowed, as did the white quills and pouch skin of the short-beaked echidna and parts of the southern hairy-nosed wombat’s pale fur. Even white cat hair lit up under UV rays.
White and light-colored fur was fluorescent for most of the species studied, and naked skin and claws glowed in many mammals as well. White or pale yellow creatures—like the polar bear, southern marsupial mole and albino wallaby—glowed the most. The dwarf spinner dolphin, which had glowing teeth, was the only species that didn’t exhibit fluorescence on the outside of its body.
The property was most common and intense in mammals living on land, underground or in trees, according to the study, though aquatic and flying mammals fluoresced as well.
This new #RSOS research investigates the phenomena of 'glowing' mammals. Read the full paper: https://t.co/tQbScTKnUq @TravouillonK @CECooperEcophys @JemmyBouzin @plani_gal @SimonWLewis pic.twitter.com/qZ7jkksuQi— Royal Society Publishing (@RSocPublishing) October 5, 2023
Whether or not this glowing ability serves an evolutionary purpose for these animals is still up for debate. Fluorescence “is likely the default status of hair unless it is heavily pigmented,” the authors write in the Conversation. “This doesn’t mean fluorescence has a biological function—it may just be an artifact of the structural properties of unpigmented hair.”
However, fluorescence was particularly widespread in nocturnal mammals, so the researchers theorize these creatures might communicate at night using their glow.
“Carnivores usually have spots or stripes on their back. I think this could be potentially a way for them to recognize each other within their own species,” Travouillon tells the Guardian. “But a lot of animals only have this glowing on their bellies, because that’s not visible to predators … maybe members of their species, when they get close, will be able to recognize them.”
In some mammals, though, this theory doesn’t hold up. The southern marsupial mole was found to have fluorescent fur, but the species is blind, writes the Guardian. Other researchers echo the idea that fluorescence might not have an evolutionary function.
“It really seems that for most, if not all, mammals, the fluorescence is a side-effect of chemicals that are present in the hair and skin, and that is not adaptive,” Alistair Evans, an evolutionary developmental biologist at Monash University in Australia who was not involved in the work, tells Newsweek.