The Curious Incident of the Platypus and Fluorescent Fur

The platypus, known to be an animal oddity, surprises the natural world with a new trait: biofluorescent fur.

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By Mandy Li

The platypus, one of nature’s curious oddities, is known for its long list of absurd traits. Endemic to Australia and affectionately dubbed “Frankenstein’s first attempt,” the platypus’s quirky characteristics include venomous spurs, an electrosensitive bill that can detect other platypuses, the ability to lay eggs despite being mammals, a beaver-like tail, and many more. Now, the platypus has yet another feature to add to its list: fluorescent fur. The discovery of the fur was accidental, as researchers and mammalogists at Northland College were experimenting with UV light on a variety of mammalian pelts and observed the fluorescent glow of the platypus.

It can all be traced back to the analysis of fluorescent flying squirrels. The discovery of fluorescent squirrels had come about due to Dr. Jonathan Martin, an associate professor at Northland College, shining his UV flashlight on a flying squirrel during a night hike. To his surprise, the squirrel glowed pink. From this, Dr. Martin was inspired to shine UV light on other specimens of flying squirrels. Each squirrel specimen emitted a similar glow, and the researchers wanted to see if other mammals also fluoresce under UV light.

Professor Paula Spaeth Anich of Northland College described, “It was a mix of serendipity and curiosity that led us to shine a UV light on the platypuses at the Field Museum. Hoping to find the trait among other distant branches of mammals, Anich also observed opossums, another member of the marsupial branch. A branch of mammals known as monotremes, represented by echidnas and platypuses, was next in line.

As Anich put it, “We pulled the monotreme drawer, and we shined our [ultraviolet] light on the platypuses. And they were incredibly, vividly fluorescent green and blue.”

The discovery was initially thought to be a product of preservation, but other preserved echidna and marsupial furs didn’t fluoresce. The similarity of the fluorescence pattern between the platypuses, flying squirrels, and other species means that the phenomenon is consistent with other mammals previously observed having fluorescent pelts.

These findings beg the question: what is the importance of fluorescence in platypus fur? Despite the sample size being too small for strong conclusions, researchers have developed several theories, all of which are based on the hunch that it may have something to do with the dark.

The earliest of these theories is that platypuses fluoresce to disguise themselves from ultraviolet-sensitive predators. Anich believes that platypuses, which are primarily nocturnal, may absorb ultraviolet light rather than deflect it onto potential predators. Biofluorescence occurs when light, often blue light, is absorbed by an organism and then re-emitted at another wavelength. This causes the light to appear in different colors such as red, purple, green, or blue. Because platypuses are nocturnal, any sort of light emission would alert a nearby predator of their presence, making them easier to be hunted. By absorbing the UV light and emitting it at different wavelengths, the light emitted is undetectable by UV-sensitive predators. This allows the platypus to escape safely without alerting any predators of their presence.

Josh Griffiths, an Australian wildlife ecologist, disagrees with this theory. “Maybe up in northern Queensland, they get chomped by a crocodile now and then, but essentially, they just don’t have any predators,” he said. Instead, Griffiths attributes the fluorescent fur to communication between individual platypuses. Most platypus detection comes from their bills, which are filled with approximately 40,000 electrosensitive receptors. The equal expression of fluorescence among male and female platypuses indicates that the trait isn’t related to sexual behaviors or elaborate platypus mating rituals, so any form of communication would likely be related to general detection. Other mammals have been reported to be sensitive to UV light, so the trait could also be present in the platypus. In their twilit environments, a trait like this could be useful for communicating beyond electrosensitive detection. A similar idea is discussed in regard to fluorescent frogs and salamanders, which may also communicate with their bright green glows.

Once they have ascertained the reason for fluorescence in the platypus, one advancement that researchers hope to make involves tracking platypuses in the wild. Platypuses are notoriously difficult to study because of their low population, which is said to be in decline since the arrival of the first Europeans in the 17th century. A study conducted in 2016 by the International Union for Conservation of Nature (IUCN) found that populations had dropped by about 30 percent on average since Europeans first arrived in Australia.

The primary causes of this decline are overhunting and habitat loss. In the 19th century, platypuses were hunted for their fur, which was often turned into slippers and rugs. More recently, the wildfires that ravaged Australia earlier this year evaporated lakes and decimated the brush where platypuses hide and interact when out of the water. The loss of bodies of water also means that platypuses are losing their sources of food and their homes. Climate change is also a large threat to the platypus population; another study by the University of Melbourne and the University of New South Wales indicates that the population could decline by up to 73 percent in the next 50 years.

Because fluorescent fur could allow scientists to track the elusive platypuses without having to handle them or interfere with their natural behavioral patterns, analyzing them may be easier in the future. Additionally, the research generated by this potential new method of tracking may aid scientists in rebuilding the platypuses' natural habitat and in their repopulation.

In addition to potentially aiding researchers in their tracking of platypuses, the fluorescent fur also has important implications for mammalogical evolution. As part of the monotreme branch, which includes echidnas, platypuses are said to have separated from other mammals approximately 166 million years ago. Platypuses may be an evolutionary oddity because they evolve ‘more slowly’ than other mammalian species. A fossil discovered in 2008 indicated that the platypuses’ slowed metabolism and generation times may have evolutionarily held platypuses back. Because platypus fossils are so few, analyzing their evolutionary history is often difficult.

However, the fluorescent fur may aid in studying the evolution of mammals. Though monotremes split from marsupials and placental mammals hundreds of millions of years ago, their shared fluorescence indicates a common trait which scientists can use to pinpoint specific evolutionary events. While the recent discovery is not enough to establish conclusive lines of evidence, seeing this trait in “all three of the major branches is indicative that it is an ancestral trait,” says Anich. She is excited about what this discovery can reveal, such as answers to questions about mammalian evolution and shared ancestry, as well as the interactions and behavior patterns of nocturnal animals.

As random as the discovery may appear, the presence of fluorescent fur in platypuses is sure to make waves in mammalogy, conservation efforts, and evolutionary science. Whether it links together mammals that may have seemed too distantly related or allows researchers to learn more about platypus habits and behavior, fluorescent fur is a curious but exciting feature bound to change the way scientists address mammals and their history. The fur may answer several questions about the unique mammals while opening up new questions about the nocturnal and mammalian world. Regardless of the evolutionary and ecological conclusions, Frankenstein's first attempt may take pride in its possession of yet another fantastically fluorescent trait.