With its venom-laced spurs, idiosyncratic duck bill, and mammalian egg-laying abilities, the platypus was already world famous as one of the weirdest animals on Earth. Now, scientists have discovered that this evolutionary oddity has yet another fascinating adaptation—its fur glows in the dark when exposed to ultraviolet light.
The new discovery represents “the first report of biofluorescence in a monotreme mammal,” the extremely rare family to which the platypus belongs, “under UV light,” according to a recent paper published in the journal Mammalia.
Biofluorescence occurs when animals absorb short wavelengths of light and re-emit longer wavelengths, causing a shift in color; it is distinct from bioluminescence, which is the biological ability to independently generate light from chemical reactions.
This fluorescent glow has been observed in birds, insects, marine life, and plants, but it had only been seen previously in two mammal families, opossums and flying squirrels. As a result of the apparent rareness of biofluorescent mammals, there hasn’t been much of an effort to seek them out—until now.
Scientists led by Paula Spaeth Anich, an associate professor of natural resources at Northland College, were inspired to look for biofluorescence in platypus after members of the team unexpectedly detected a pink glow in the fur of New World flying squirrels while studying lichens with a blacklight.
Anich and her colleagues discovered that platypus share the glowing fur by exposing three stuffed specimens to UV light in a dark room.
“It was a mix of serendipity and curiosity that led us to shine a UV light on the platypuses at the Field Museum,” said Anich in a statement. “But we were also interested in seeing how deep in the mammalian tree the trait of biofluorescent fur went.”
“It’s thought that monotremes branched off the marsupial-placental lineage more than 150 million years ago,” she continued. “So, it was intriguing to see that animals that were such distant relatives also had biofluorescent fur.”
Anich and her colleagues observed the greenish-to-cyan color on a Tasmanian male and female from the Field Museum of Natural History in Chicago, as well as a male from the Australian mainland that is now stored at the University of Nebraska State Museum. Though the collection date of the Field Museum male is not known, the other two specimens are each over a century old: the Chicago female dates back to 1889 and the Nebraska male was collected in 1909.
The new identification of biofluorescence in animals such as platypus and flying squirrels suggests that this adaptation may be more widespread in mammals than expected. Scientists think that the adaptation may play many roles in other species, such as luring prey, sexual selection, intraspecies communication, and camouflage. However, it’s still not clear why platypus have evolved the colorful display.
“While biofluorescence in response to UV light was seen in all of the platypus specimens we examined, the small sample size limits our ability to draw conclusions about the ecological function of this trait,” Anich and her colleagues said in the study.
“The male and female specimens biofluoresced in the same patterns and intensity; therefore, it appears that the trait is not sexually dimorphic,” the team added. “We are confident that the fluorescence we observed is not a property of museum specimens in general.”
The team speculated that platypus glow may serve as a kind of invisibility cloak for UV-sensitive predators, but noted that field observations of wild platypus would ultimately be needed to unravel the mysteries behind the fluorescent fur.
One thing’s for certain, though: The platypus continues to live up to its reputation as one of the weirdest animals on Earth.