By the light of day, the South American polka dot tree frog, otherwise known as the Hypsiboas punctatus, has a pale green colouring, with small red dots littered across its back. Underneath ultraviolet light, it undergoes a brilliant transformation – glowing an almost neon green.
Carlos Taboada, a herpetologist at the University of Buenos Aires in Argentina, co-author of the study published by the Proceedings of the National Academy of Sciences of the United States of America, collected the frogs near Santa Fe. Upon further research into their green fluorescence, the team found that three molecules – hyloin-L1, hyloin-L2 and hyloin-G1 were present in the frog’s skin and lymph tissue. The secretions from these areas contained the chemicals necessary to absorb light and are similar to those found in plants.
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Taboada explained in a statement that this fluorescence is a rarity amongst terrestrial animals, and until now, the ability to absorb and re-emit light in this manner has been unheard of in amphibians: “This phenomenon is uncommon in tetrapods, being restricted mostly to parrots and marine turtles.”
Fluorescence is different from bioluminescence, a trait that certain sea creatures possess. Whereas bioluminescence creates light through a complex chemical reaction, and can work even in the darkest parts of the ocean, fluorescent creatures rely on the absorption of light in order to create this glow. In essence, fluorescence is the ability to absorb short-wavelength electromagnetic radiation and reemit this at longer wavelengths.
The bioluminescent deep-sea octopus Stauroteuthis syrtensis is able to lure prey with a series of flashing photophores within the tentacles, creating a hypnotic lure. By contrast, it is unclear why the polka dot tree frog has a fluorescent ability, but possible explanations could be for the purpose of communication, or to attract a mate.
The fluorescent colour of the tree frog came as a surprise – not due to its ability to absorb light, but due to the fact that it glowed green. Since the frogs contained the pigment biliverdin, herpetologists had anticipated it would emit a faint red hue. Instead, they found the frogs possessed a powerful green glow.
The sheer strength of light emitted by the frogs is surprising. They can project up to 18 per cent as much visible light as a full moon. Taboada intends to study the photoreceptors of the frogs to test whether this light emission correlates with the necessary visual requirements for the frog to see clearly.
This article was originally published by WIRED UK
