The glowing secret that mammals were hiding

At first, it seemed like another whim of two already unusual animals: flying squirrels and platypuses were found to be fluorescent, absorbing invisible ultraviolet rays and emitting them in a stunning pink or bright cyan color.

But they are not alone. According to the paper Published in the journal Royal Society Open Science This month, lions, polar bears, scale-tailed opossums and American pikas also shine. The same goes for every species of mammal that a group of scientists can get their hands on.

While this large survey of museum specimens reveals no broad evolutionary benefit, it overturns the view of mammalian fluorescence as an accidental and mysterious whim. Instead, the trait appears to be “basically the default,” said Kenny Travoillon, curator of mammalogy at the Western Australian Museum and lead author of the study.

A fuller spectrum

While scientists have documented fluorescent mammals More than a centuryThere has been increasing interest in the topic in the past few years. Researchers who shine black lights on backyards, forests and museum vaults have come up with a box of discoveries to color.

Most of the resulting studies focused on one species, or a few, “trying to better understand the nuances of the trait” in a single species of mammal, he said. Eric Olson, an associate professor of natural resources at Northland College in Ashland, Wisconsin, who helped detect luminescence in flying squirrels, platypus, and springbirds.

He was not involved in the new study, in which researchers examined museum specimens of 125 species belonging to more than half of the existing mammalian families, from Antilocapridae to Vespertilionidae. (Vespers bats).

They found some brilliance in all of them. Scanning ““It clearly identifies a broad distribution of this trait within mammals, which is something I did not expect,” Dr. Olson said.

Conservation reservations

Dr Travoillon said the idea for such a survey was sparked in 2020 when the discovery of the platypus prompted researchers at the Western Australian Museum to point a UV lamp at their own collections. They found turquoise wombats and flying foxes with shiny sides. But were these stuffed specimens really glowing? Or could something else be to blame, like preservatives or fungi?

In collaboration with colleagues from Curtin University in Perth, the team used a photometer to expose the samples to ultraviolet light and analyze any fluorescence emitted. They also tested newly obtained specimens of several species — including the platypus, koala, and echidna — before and after they were preserved.

Preservation with borax and arsenic affected the intensity of fluorescence, increasing it in certain cases while decreasing it in others. But it never created fluorescence where there was none.

This before-and-after testing “is a major contribution to understanding the effects of museum conservation on fluorescence,” said Linda Reinhold, a zoologist at James Cook University in Australia who served as a peer reviewer for the study.

Bright idea

As they performed these tests, the researchers noticed a pattern: Light-colored areas of fur and skin fluoresced uniformly.

They wondered whether this was universal across mammals, so they decided to expand their research, drawing on museum collections ““As many species as possible in the mammalian family tree,” Dr. Travoillon said.

One by one, the mammals were subjected to spectrophotometry. The koala’s light belly and ears shine green. The bat’s bare wings, ears, and nose leaf gave it a pale yellow color. Even the white fur of house cats emits a faint luster.

Eventually, Dr. Travoillon said, “it started to get a little boring.” “We were looking at them and saying, ‘Oh yeah, it’s glowing.'”

In the end, samples from all 125 species tested showed some degree of fluorescence. Most often, it came from structures made of unpigmented keratin, such as white fur, the bare skin of pouches and claw pads, or tools such as quills, claws, and whiskers. The wallaby with albinism, a condition in which the production of melanin pigment is interrupted, glowed “very intense” blue, while the less luminous specimen, the dwarf spinner dolphin, only glowed in the teeth, Dr. Travoillon said.

In some cases, the dyed fur also fluoresces, suggesting the possibility of other substances, as previously seen in spring hares, whose fluorescence does not match their color pattern, and has been traced to pigments called porphyrins.

The prophetic mole

As in the past, the discovery of ultraviolet fluorescent organisms poses a difficult question: Can mammals even detect these glows in nature?

Often times, the images of spotted spring hares and radiant polar bears in articles like this are captured in artificial conditions that heighten their impact. They do not reflect appearances in the real world, as the strength of the rest of the light spectrum overwhelms these hidden colors.

When the team looked for trends, they found that nocturnal animals had greater fluorescence in terms of surface area than diurnal animals, although the difference was small.

In addition, “prey species tend to place them on their abdomens, but carnivores tend to place them on their backs,” Dr. Travoillon said, suggesting a potential brightening effect under moonlight could help predators recognize their species. Other experts, like Ms. Reinhold, wonder whether moonlight would provide enough ultraviolet radiation to make this happen.

But it’s hard to imagine any benefit for some animals recently added to the glowing chart, such as the southern marsupial mole, which is blind and spends its entire life underground, Dr. Travoillon said.

Ines Cottell, a professor of behavioral ecology at the University of Bristol in England who was not involved in the study, said it should put an end to the idea “that fluorescence in animals is necessarily a signal.”

But we may not be at the end of the rainbow. Given the study’s findings about potentially confounding conservation impacts, examining live animals of these species could be “astonishing,” Ms. Reinhold said. “I hope this study inspires others to go into the wilderness with a UV flashlight (and a proper permit, of course).”