Nightclubgoers will be familiar with the mind-blowing experience of seeing clothing “glow” under ultraviolet (UV) light, an effect known as fluorescence.
Now, an Australian study shows that this phenomenon is widespread in mammals, including the domestic cat species (Felis catus).
In addition to cats, fluorescence was found in 125 species, including bats, koalas, zebras, moles, polar bears and dolphins, they report.
In the same way that it helps us see other people crossing the dance floor, it can help animals notice each other in low-light conditions, such as in the dead of night.
Previous studies have shown that fluorescence is observed among birds, reptiles, corals, mollusks, scorpions and other arthropods, amphibians such as frogs, and even fish.
Fluorescence is widespread in mammals, including the domestic species of cat (Felis catus), report experts at Curtin University in Perth, Australia (file photo)
The researchers found clear evidence of fluorescence in the white fur, spines, and even the skin and nails of koalas, Tasmanian devils, short-beaked echidnas, southern hairy-nosed wombats, quendas (bandicoots), older bilbies and even cats.
What is fluorescence?
Fluorescence is the ability of certain chemicals to emit visible light after absorbing radiation that is not normally visible, such as ultraviolet (UV) light.
Ultraviolet light is a form of electromagnetic radiation, but it is invisible to the human eye.
Fluorescence is quite common among animals; Birds, reptiles, amphibians, fish, corals, mollusks and, most famously, scorpions and other arthropods have been reported.
Recently, several mammals have been reported to “glow” fluorescently under ultraviolet light, including Australia’s beloved platypus.
Experts already knew that bones and teeth glow, as do white hair and nails in humans, but until now no one knew how common it was among mammals.
The new study, led by Dr Kenny J. Travouillon, a palaeontologist at the Western Australian Museum in Perth, now confirms “widespread fluorescence in mammals”.
“Almost all the mammals we studied showed some type of fluorescence,” he said in an article for The conversation.
‘We believe that fluorescence is very common in mammals; in fact, it’s probably the default state of hair, unless it’s heavily pigmented.”
Fluorescence may have evolved in animals as a useful biological function, such as for communications in nocturnal species, although this is not certain.
“It may simply be an artifact of the structural properties of non-pigmented hair,” Dr. Travouillon said.
Preserved wombats seen glowing under ultraviolet light (pictured). Those that are alive or recently dead may be even more fluorescent.
Fluorescence spectra of frozen specimens of the domestic cat species (Felis catus). The cat’s dark fur was not fluorescent, but the white fur was.
The image shows fluorescence from preserved and frozen specimens of platypus (a), koala (b) and Tasmanian devil (c). The photo shows frozen specimens under ultraviolet light, using a filter.
“However, we suggest that fluorescence may be important for illuminating the pale-colored parts of animals that are used as visual cues.
“This could improve their visibility, especially in low light conditions, much like fluorescent optical brighteners added to white paper and clothing.”
Dr Travouillon and his colleagues studied preserved and frozen specimens from museums and wildlife parks, including the Western Australian Museum and the Tasmanian Museum and Art Gallery.
The researchers started with the platypus to see if they could replicate the fluorescence previously reported in another study in 2020.
At that time, the fur of the three platypus specimens was uniformly brown under visible light, but under ultraviolet light it appeared green or cyan.
“We photographed preserved and frozen platypus specimens under ultraviolet light and observed a fluorescent glow (although quite faint),” Dr. Travouillon said.
They then used a technique called fluorescence spectroscopy, which shines various light sources onto the samples and records specific “fingerprints” of the brightness, to confirm that what they saw was indeed fluorescence.
After repeating this process with other mammals, they found clear evidence of fluorescence in koalas, Tasmanian devils, short-beaked echidnas, southern hairy-nosed wombats, bandicoots, greater bilbies, and even cats.
Orange leaf-nosed bat under ultraviolet light. The Australian species rests in caves, eats moths and is sensitive to human intrusion.
Areas of fluorescence included white and light fur, quills, whiskers, claws, teeth, and some bare skin.
For the domestic cat, the dark fur was not fluorescent, but the white fur was, with similar intensity to the platypus.
The team admits that they studied preserved animals that had been dead for a long time, but those that are alive or recently dead may be even more fluorescent.
“We suggest that future studies focus on non-conserved animals,” they conclude in their article, published in the journal Royal Society Open Science.
‘These would not be affected by the possible degradation of fluorescent materials or by preservation chemicals.
“Species of interest would include those with highly patterned skins, which may be important for visual signaling or camouflage, and those with highly specialized life histories.”
NOCTURNAL ANIMALS REST DURING THE DAY AND ARE ACTIVE DURING THE NIGHT
Some animals, including frogs, depend on the starry sky to navigate at night (file photo)
Nocturnal animals rest during the day and are active at night.
This means they hunt, mate, and perform other necessary survival activities without the help of the sun.
Many nocturnal animals have built-in bodily functions that help them survive during nighttime hours, when it can be difficult to see.
For example, the eyes of some nocturnal animals are larger, allowing them to function satisfactorily even in the dark.
Additionally, some nocturnal animals have extremely sensitive ears that can help them defend themselves in dark environments.
Lastly, some have enhanced senses of smell, touch, and taste to help them function better at night.