Strange Made Stranger: Platypuses Glow Under UV Light

What could possibly make the duck-billed platypus stranger that it already is? Researchers found that their fur also glows blue when placed under ultraviolet (UV) light.

Platypuses are some of the strangest creatures on the planet. They're one of the very few mammals that lay eggs, they have bills and webbed feet similar to ducks', their tails look rather like beaver tails and, apparently, they also glow an eerie shade of blue-green when exposed to UV light.

The latter was recently discovered by a team of scientists who were actually studying biofluorescence, the means by which creatures absorb and re-emit wavelengths of light, in the museum specimens of another species. According to a news release from De Gruyter, the team made the discovery while looking at flying squirrel museum specimens.

They had previously observed pink biofluorescence in flying squirrels and were confirming it in the museum specimens when they decided to also check the museum's platypus samples for the trait.

There, they discovered that platypuses also possess biofluorescence, with their brown fur exhibiting a greenish glow under the UV light. The researchers tested another sample in different museum and also observed the glow.

"Here we document the discovery of fluorescence of the pelage of the platypus (Ornithorhynchus anatinus)—to our knowledge, the first report of biofluorescence in a monotreme mammal under UV light," the researchers wrote in the study.

In total, the researchers observed platypus biofluorescence in three museum samples, two of which were from the Field Museum of Natural History and the other from the University of Nebraska State Museum, the news release noted.

"It was a mix of serendipity and curiosity that led us to shine a UV light on the platypuses at the Field Museum. But we were also interested in seeing how deep in the mammalian tree the trait of biofluorescent fur went," study lead Paula Spaeth Anich of Northland College said in the news release. "It's thought that monotremes branched off the marsupial-placental lineage more than 150 million years ago. So, it was intriguing to see that animals that were such distant relatives also had biofluorescent fur."

But what could platypuses possibly have use for biofluorescence? It's possible, the researchers say, that platypuses use this trait to interact with each other in the dark and to reduce their visibility to UV sensitive-predators.

It would be particularly useful since platypuses are most active at night and during low-light environments at dawn and dusk. However, field research is needed to confirm these hypotheses, the researchers said.

Biofluorescence has been observed in many other animals such as fishes, reptiles and amphibians, but only few mammalian species are known to posses biofluorescence, including the opossum and the flying squirrel.

"The discovery of biofluorescence in the platypus adds a new dimension to our understanding of this trait in mammals," the researchers wrote. "Biofluorescence in mammals is not restricted to a few closely related specialists; instead, it appears across the phylogeny, which begs the question: Is biofluorescence an ancestral mammalian trait?"

The study is published in the De Gruyter's journal Mammalia.