Scientists discover that platypuses glow in the dark

The platypus just became known for another unusual characteristic: It is biofluorescent.

A team of U.S. scientists accidentally discovered this when one of them shone an ultraviolet (UV) light on two platypus specimens at the Field Museum of Natural History in Chicago. The uniformly brown fur of the platypus turned green to cyan under the light.

The researchers had been looking at biofluorescence in flying squirrel specimens at the museum, and decided to shine their light on other specimens. Their research appears online in the journal Mammalia, published Oct. 15.

The researchers verified their results on another platypus specimen from New South Wales now at the University of Nebraska State Museum in Lincoln.

Biofluorescence is the phenomenon of living organisms to absorb short wavelengths of light and re-emit them as long waves. It's rare among mammals and, so far, is known to occur only among creatures who are active at night, dusk and dawn.

The platypus (Ornithorhynchus anatinus) is a semi-aquatic mammal found only in Australia and Tasmania. It has an improbable combination of features--a duck-like bill that can sense electricity, otter-like webbed feet and a beaver tail. Its fur is waterproof and the females lay eggs. 

In North America, the authors note, biofluorescence of fur or hair has been found in marsupial opossums and placental flying squirrels. The platypus is in a third taxa; monotremes. The name monotreme comes from the Greek word for single, monos, and hole, trema. Monotreme (single hole) refers to this taxa's characteristic of having only one opening for both digestive and urogenital functions.

Finding biofluorescence in a a monotreme mammal, the authors note, means that it appears in taxa "inhabiting three continents and a diverse array of ecosystems" representing the major lineages of mammals. This observation has caused them to ask, "Is biofluorescence an ancestral mammalian trait?"

The research raises questions about why biofluorescence might be important for animals. Perhaps it is ecologically useful in the low-light environments that the biofluorescent animals inhabit. Perhaps, the authors suggest, biofluorescence "reduces the visibility of the platypus to UV-sensitive predators." The biofluorescence would absorb some UV light, reflecting out less of it and making the platypus less visible.

The authors also suggest that because the platypus navigates using "mechanoreception and electroreception," biofluorescence might be less important for its interactions with other platypuses than with interactions with other species.

"It was a mix of serendipity and curiosity that led us to shine a UV light on the platypuses at the Field Museum," lead author Paula Spaeth Anich said in a news release on the discovery. "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. So it was intriguing to see that animals that were such distant relatives also had biofluorescent fur."

Anich is an associate professor of biology and natural resources at Northland College in Wisconsin.

The researchers plan to work with Australian scientists to look at biofluorescence in wild animals. They are also working on exploring the phenomenon of biofluorescence among other mammals.