Some mammals have fur that displays a striking glow under UV light

Australia teems with wildlife known for its vivid colors and striking fur patterns. Yet, beneath the surface, some creatures hide a mesmerizing secret – their fur glows under ultraviolet light.

Photoluminescence, a phenomenon seen in fish, birds, and even some plants, also occurs in mammal fur, though it remains poorly understood.

Intrigued by this hidden brilliance, a team of researchers at James Cook University embarked on a quest to uncover the molecules responsible for these glowing hues.

Linda Reinhold led the study that aimed to decode the chemistry behind photoluminescence in several Australian mammals.

“Rats, along with bandicoots, possums, bats, tree-kangaroos and many other creatures in Australia and around the world are photoluminescent; they glow under ultraviolet, violet or blue light,” she said.

Mammal fur samples for UV light analysis

To unlock the mystery, the team turned to roadkill.

By collecting fur from recently deceased northern long-nosed and northern brown bandicoots, northern quolls, coppery brushtail possums, Lumholtz’s tree-kangaroos, pale field rats, and platypuses, they assembled a diverse array of samples.

Shaved fur, wrapped in aluminum foil to prevent photobleaching, was stored at -18°C (-0.4°F) . The researchers employed high-performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS) to analyze the molecular makeup of the fur.

Each strand held potential clues, waiting to be unearthed.

Different fur colors seen under UV light

Under ultraviolet light, the bandicoot fur erupted in a vivid array of colors. Reinhold and her colleagues sought to identify the luminophores, the molecules responsible for this dazzling display.

“The fur of the Australian northern long-nosed and northern brown bandicoots photoluminesces strongly, displaying pink, yellow, blue and/or white colors. We wanted to find out whether the luminophores present in bandicoot fur might be common across multiple species,” explained Reinhold.

The study revealed two primary classes of luminophores: porphyrin derivatives and tryptophan metabolites. Yet, each species exhibited its own distinct luminescent signature.

Fur compounds causing pink and orange glow

Porphyrins, a group of organic compounds linked to heme, emit pink and orange hues when exposed to ultraviolet light.

The researchers found several porphyrin derivatives, including protoporphyrin, coproporphyrin, uroporphyrin, and heptacarboxylporphyrin, in the fur of bandicoots, quolls, and possums.

Furthermore, the coppery brushtail possum held another surprise.

“Unexpectedly, we also found a contributing cause of the color of coppery brushtail possum fur – not photoluminescent, but a strong purple coloration in white light – a match for the molecule indigo – which is also extracted as a dye from plants,” said Reinhold.

Indigo in possum fur under UV light

Indigo, known for its use in fabric dyes, surfaced as a startling discovery in possum fur. The compound gave the fur a striking purple sheen under white light, an unusual feature not previously associated with photoluminescence.

Was this the only instance of indigo in mammalian fur? The researchers couldn’t say for sure. The finding suggested the presence of yet-undiscovered pathways for fur coloration.

Luminescent legacy of tryptophan

While porphyrins dominated the pink and orange hues, tryptophan metabolites contributed to yellow and blue photoluminescence. Tryptophan, an amino acid that is essential for protein synthesis, breaks down into metabolites that can emit light.

In this study, kynurenic acid and N-acetylkynurenine emerged as the key players. The pale field rat’s fur contained these compounds, and it glowed yellow under ultraviolet light. Yet, curiously, the other species showed no trace of tryptophan derivatives.

Lumholtz’s tree-kangaroo

Not every mammal in the study fit neatly into the porphyrin-tryptophan framework. Fur from the Lumholtz’s tree-kangaroo, for instance, displayed a captivating blue-lavender glow, particularly under 365 nm light.

This glow couldn’t be attributed to known luminophores. Instead, the researchers detected molecules with unique masses, hinting at unidentified compounds with unusual chemical structures.

The platypus and its subdued glow

Unlike its colorful counterparts, the platypus presented a more subdued photoluminescence – a greenish tint with faint pink undertones. Despite its muted appearance, the platypus fur still contained porphyrins.

Why such a difference? Was the photoluminescence a vestigial trait, or did it serve a specific purpose? The study left these questions open, inviting further exploration.

Evolutionary significance of photoluminescence

Why do these mammals glow in the first place? The researchers proposed several hypotheses. Photoluminescence might serve as a form of communication, a warning signal, or even a camouflage mechanism.

Alternatively, the phenomenon could indicate metabolic waste products being excreted through fur. Protoporphyrin, a common porphyrin derivative, is a byproduct of heme metabolism and is known for its toxicity in high concentrations.

Fur might act as a dumping ground, releasing excess porphyrins to prevent their buildup in the body.

What remains unexplored

Despite the wealth of data collected, many mysteries still linger. Out of 70 molecular ions identified in the fur extracts, only a handful matched known luminophores.

Over 57 fur compounds remained unidentified, each potentially holding new insights into the chemistry of mammalian fur under ultraviolet light.

Could some of these unknown molecules explain the intense blue and lavender glow seen in the Lumholtz’s tree-kangaroo? Could others account for the unique hues of the coppery brushtail possum?

Moving forward: The next steps

The study provided a glimpse into the chemical complexity of photoluminescent fur, yet it left many stones unturned. Reinhold and her team plan to continue analyzing the unidentified molecules, seeking to determine their structure and potential function.

Understanding why certain mammals glow could also shed light on broader ecological and evolutionary patterns. Do photoluminescent compounds play a role in mate selection or predator avoidance? Could they help scientists track metabolic processes in wild populations?

UV light uncovers hidden fur glow

Photoluminescence may seem like a rare and exotic phenomenon, but this study suggests otherwise. Australian mammals, from bandicoots to platypuses, harbor a secret world of hidden hues, visible only under ultraviolet light.

By probing deeper into the chemistry of fur, Reinhold and her team have opened a window into this world, revealing molecular secrets that remain largely untapped.

Yet, the work is far from complete. Each newly discovered compound offers a tantalizing glimpse of what lies beneath the surface – an intricate web of biochemistry that glows softly in the dark.

The study is published in the journal PLOS One.

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