Scientists discover that "fluorescence is very common in mammals"

Researchers Kenny Travouillon (Western Australian Museum), Christine Cooper (Curtin University), Jemmy Bouzin (Curtin University), Linette Umbrello (Queensland University of Technology), and Simon Lewis (Curtin Univesrity) recently published an article entitled "All-a-glow: Spectral characteristics confirm widespread fluorescence for mammals," in the journal Royal Society Open Science. While it's well known that some animals—birds, reptiles, amphibians, fish, scorpions and other arachnids and arthropods—"glow" under ultraviolet light, the researchers sought to understand just how widespread this kind of fluorescence is, and were especially interested in learning about the phenomenon among mammals. 

Turns out, it's much more common than previously thought. 

In a recent piece in The Conversation, the researchers explain that they conducted tests on preserved and frozen specimens from the Western Australian Museum's collection, and found 125 fluorescent species of mammal, from every known order. They also sought to understand what might explain this glow—was it really fluorescence? Or was it caused by something from the process of preserving the animals for the museum? Through a technique called fluorescence spectroscopy, they were able to determine that, in fact, it was the animals themselves glowing and not the the process of preservation. They explain: 

We . . . found clear evidence of fluorescence in the white fur, spines and even skin and nails of koalas, Tasmanian devils, short-beaked echidnas, southern hairy-nosed wombats, quendas (bandicoots), greater bilbies and even cats.

Both fresh-frozen and chemically treated museum specimens were fluorescent. This meant it wasn't preservation chemicals such as borax or arsenic causing the fluorescence. So, we concluded this was a real biological phenomenon. . . 

In particular, we noticed that white and light-coloured fur is fluorescent, with dark pigmentation preventing fluorescence. For example, a zebra's white stripes fluoresced while the dark stripes didn't.

They also discovered that nocturnal species were more likely to fluoresce, and that aquatic animals were less likely to fluoresce than those that burrow or live in trees or on land. They go on:

Based on our results, we think fluorescence is very common in mammals. In fact, it is likely the default status of hair unless it is heavily pigmented. This doesn't mean fluorescence has a biological function – it may just be an artefact of the structural properties of unpigmented hair.

However, we suggest florescence may be important for brightening pale-coloured parts of animals that are used as visual signals. This could improve their visibility, especially in poor light – just like the fluorescent optical brighteners that are added to white paper and clothing.

Here's the abstract of the research article:

Mammalian fluorescence has been reported from numerous species of monotreme, marsupial and placental mammal. However, it is unknown how widespread this phenomenon is among mammals, it is unclear for many species if these observations of 'glowing' are true fluorescence and the biological function of fluorescence remains undetermined. We examined a wide range of mammal species held in a museum collection for the presence of apparent fluorescence using UV light, and then analysed a subset of preserved and non-preserved specimens by fluorescent spectroscopy at three different excitation wavelengths to assess whether the observations were fluorescence or optical scatter, and the impact of specimen preservation. We also evaluated if fluorescence was related to biological traits. We found that fluorescence is widespread in mammalian taxa; we identified examples of the phenomena among 125 species representing all 27 living mammalian orders and 79 families. For a number of model species, there was no evidence of a corresponding shift in the emission spectra when the wavelength of excitation was shifted, suggesting that observations of 'glowing' mammals were indeed fluorescence. Preservation method impacted the intensity of fluorescence. Fluorescence was most common and most intense among nocturnal species and those with terrestrial, arboreal and fossorial habits, with more of their body being more fluorescent. It remains unclear if fluorescence has any specific biological role for mammals. It appears to be a ubiquitous property of unpigmented fur and skin but may function to make these areas appear brighter and therefore enhance visual signalling, especially for nocturnal species.

You can read the published study here. You can also read the rest of the more general-public friendly version of their research in The Conversation.