Biofluorescence occurs when fluorescent proteins in organisms reflect absorbed light. Previously associated with organisms such as algae, fish, and amphibians, scientists report the first observations of a blue-green hue emitted from the Australian platypus.
The study was recently published in the journal Mammalia. This is the first time that scientists have associated biofluorescence with monotreme species which are composed of platypus and echidnas.
So far, the unique glow has been observed in only a handful of mammal species including flying squirrels and opossums, both native to Australia and Tasmania. Also found in two other continents, these species represent the major lineages of mammals, wrote the authors.
Studying biofluorescence in nature has been focused more on flora, fungi, insects, and birds. Discovering the glowing property in animals has been surprising, such as the discovery of a fluorescent sea turtle in 2015 when researchers were looking for fluorescent coral.
In 2017, scientists recorded the first account of a glow-in-the-dark frog in Argentina. Researchers sought the polka-dot tree frog since its translucent skin produces biliverdin or a blue-green bile pigment. It raised the question if fluorescent properties of animals have a specific function or is a "non-functional outcome of certain pigments' chemical structure," described Maria Lagorio from the University of Buenos Aires.
Linking the newly discovered glowing property of platypus to the opossum and squirrel, they all share a nocturnal lifestyle - the time when their UV light shines the strongest. The team hypothesized that mammals with a nocturnal and crepuscular (active during dawn/dusk) lifestyle may have glowing fur.
Paula Anich from Northland College said that "it was a mix of serendipity and curiosity that led us to shine a UV light on the platypuses at the Field Museum." The researchers are also interested if biofluorescence in mammals is an ancient trait, and if more species have the same characteristic.
For Survival or Mating?
Different species have been observed to use their glow for various reasons. For example, fluorescent bird feathers are significant in mating rituals while fish use their glow for communication. On the other hand, tarantulas that glow blue have been linked to communicating with others while a green glow is associated with tree-dwelling species and camouflage.
With the platypus, both sexes have a similar glow, meaning that it is not a trait involved with mating. Also, they swim with their eyes closed so it may not be for communication purposes either. An alternative theory is that the glow is a camouflage tactic from UV-sensitive predators.
The first glowing platypus was observed at the Field Museum of Natural History in Chicago Illinois. The research team then examined two platypi in Tasmania. While appearing "uniformly brown under visible light," the animals glowed "green to cyan under UV light", wrote the authors. "The discovery of biofluorescence in the platypus adds a new dimension to our understanding of this trait in mammals," they concluded.
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