An interesting observation of fluorescence in ultraviolet (UV) light has been reported in museum specimens of the Platypus (Ornithorhynchus anatinus); the fur shone green-cyan. The Platypus has thus joined a handful of other mammals in displaying this phenomenon.
The functional significance, if any, remains unknown. The authors come up with a suggestion that absorption of UV (with emittance of light of longer wavelengths) might reduce the animal’s visibility to predators equipped with an ability to see UV. How this might work in a crepuscular or nocturnal animal I do not know. Or it could it could increase visibility of one platypus to another platypus by shifting invisible UV radiation to the visible range as darkness falls. Or it could have no biological significance whatsoever, being merely a physical property of the fur that has not been selected against; an epiphenomeon, in other words.
An example I quote when talking about animal coloration is that biochemical pathways that produce coloured compounds may be selected against in animals that live in daylight. By contrast in the lightless depths of the ocean or in caves an animal can be any colour. It just does not matter. If a biochemical pathway advantageous to, say, conserving energy, were to produce a colourful compound as an intermediate, it would be of no consequence. Similarly, blind cave fish or salamanders are often white. Why waste energy producing pigment when nothing can see them?
As I was writing this Jerry Coyne has also commented on this paper here. He also raises the possibility that it is a biological epiphenomenon.
This is clearly a phenomenon to investigate even if it turns out to be biologically unimportant. I can already envisage a few Australians out in the bush shining a UV lamp at platypuses in the water. If I were there I would be. I like watching them anyway, having been lucky enough to see them wherever we went looking for them in Queensland and Tasmania.
I must also tell my physicist friends. Just what is it in the fur of these few species that is acting as fluorophore?
Anich PS, Anthony S, Carlson M, Gunnelson A, Kohler AM, Martin JG, Olson ER. 2020. Biofluorescence in the platypus (Ornithorhynchus anatinus). Mammalia https://doi.org/10.1515/mammalia-2020-0027 published online October 15, 2020
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