It is a surprising and so far unexplained phenomenon: in some mammals such as flying squirrels, platypuses or gophers, the fur glows bluish, greenish or reddish in UV light in dark surroundings. Researchers previously assumed that photoluminescence or biofluorescence is used for camouflage, to attract or to communicate with other species. A working group headed by Séverine Toussaint from the Humboldt University in Berlin has now examined the skins of various mammal specimens in museums and found that the glow apparently has no ecological function, but is simply a side effect.
As the researchers report in the journal “Integrative Zoology,” the substance porphyrin causes the play of colors. Porphyrins are chemical dyes of organic origin. In the mammalian body, they serve as building blocks for various proteins. If too many accumulate, the body stores them in the hair. Otherwise there is a risk of the animal’s skin becoming sore from the substance.
In principle, porphyrin is likely to be found in the hair of many mammalian species. However, it decomposes rapidly when exposed to sunlight. This should explain why researchers have so far documented photoluminescence primarily in nocturnal and crepuscular animals. They are less exposed to sunlight and the porphyrin in their fur stays longer.
The scientists working with Toussaint therefore do not attribute a special camouflage or intraspecific communication function to the glowing fur. Also because radiating only occurs under special circumstances when a concentrated UV beam hits the fur in a dark room. This situation probably almost never occurs in nature.
The phenomenon of photoluminescence has been known for a long time. For example in invertebrates such as scorpions. They emit bluish light in the ultraviolet. Experts have so far explained the glow of scorpions as sun protection, attractants for reproductive partners or to ward off parasites.