Cats glow in the dark? Fluorescence found to be very common in mammals

Recently, the phenomenon of fluorescence when exposed to ultraviolet light has been observed in various creatures, including birds, reptiles, insects, and fish. The prevalence of this occurrence in mammals, however, remained largely unexplored.

Now, a team of researchers led by the Western Australian Museum and Curtin University, has found that fluorescence is remarkably prevalent among mammals.

Focus of the study 

The experts analyzed 125 mammalian species, both preserved and frozen, from museum collections to determine the existence of “apparent fluorescence” when exposed to UV light. They were surprised to find that every mammalian specimen exhibited at least some degree of  fluorescence. 

These mammals include familiar creatures like domestic cats (Felis catus), as well as polar bears, bats, mountain zebras, wombats, dwarf spinner dolphins, leopards, and even the Tasmanian devil. 

Many sources of fluorescence 

The sources of these fluorescent compounds ranged from bones and teeth to claws, fur, feathers, and even the skin, while the range of fluorescent colors displayed was broad, encompassing hues from red and yellow to green, pink, and blue.

“We were quite curious to find out about fluorescence in mammals,” said lead author Kenny Travouillon, the Mammalogy curator at the Western Australian Museum. “By using the spectrophotometer in the School of Molecular and Life Sciences at Curtin University, we were able to measure the light that was emitted from each specimen when exposed to UV light.”

What causes fluorescence?

From a scientific standpoint, fluorescence occurs when certain chemicals, like proteins or carotenoids present on a mammal’s exterior, absorb light and then re-emit it at longer and lower-energy wavelengths, resulting in glowing colors that may be pink, green, or blue.

Interestingly, the study also discovered that the iconic platypus is among the creatures that fluoresce under UV light.

“To date, reports of fluorescence among mammals have been limited to a relatively small number of species,” the authors reported. “Here, we are able to reproduce the results of these previous studies and observe apparent fluorescence in additional species: we report fluorescence for 125 mammal species.”

Fur color variations

Lighter-furred mammals, accounting for roughly 86 percent (107 out of 125) of the species examined, exhibited the most noticeable fluorescence. On the other hand, the fluorescent traits in dark-furred creatures like the Tasmanian devil were subdued due to melanin’s masking effect. 

“There was a large amount of white fluorescence in the white fur of the koala, Tasmanian devil, short-beaked echidna, southern hairy-nosed wombat, quenda, greater bilby, and a cat – and while a zebra’s white hairs glowed, its dark hairs did not,” explained Travouillon.

Biological significance 

In a notable exception, the dwarf spinner dolphin showcased no external fluorescence. Only its teeth exhibited this trait. Fluorescence was found to be most common and most intense among nocturnal species and those with terrestrial, arboreal, and fossorial habits.

While the study unequivocally confirms the prevalence of fluorescence in mammals, the scientific community continues to debate its potential biological significance, with some positing it might merely be a by-product of their surface chemistry. “For most fluorescent animals there is insufficient information to evaluate,” the authors said.

Looking ahead, the researchers noted a particular mammalian group absent from their data – the lemurs. They anticipate this group will also reveal fluorescent members due to the prevalence of white fur. However, they concluded that future studies should focus on non-preserved animals but rather on living or freshly dead creatures.

The study is published in the journal Royal Society Open Science.