A team of researchers working in Argentina has found the first fluorescent frog known to science, a new study in the Proceedings of the National Academy of Sciences reports.
The species — known as the South American polka dot tree frog (Hypsiboas punctatus) — appears to be mixed shades of greens, reds, and yellows under normal light. However, when the light is dim, it gives off a sharp green-and-blue glow.
This is surprising because, while many animals are capable of fluorescence, almost all of them are aquatic. It is very rare to see the ability in terrestrial creatures, and it has never been recorded in amphibians before. Not only that, the polka dot tree frog uses fluorescent molecules that have never been noted in any other animal.
Unlike bioluminescence — by which species generate their own light — fluorescence requires some light absorption to work. It cannot happen in total darkness. The only land animals it has been noted in are parrots and some scorpions. Researchers are not sure why those animals have the trait, but many believe it is related to communication, mate attraction, or camouflage.
The reason researchers studied this process in the polka dot tree frog is because it has a pigment known as biliverdin. That trait commonly turns amphibian’s tissues and bones green, but in some insects, it also can lead to fluorescence.
While the pigment did not have the effect on the polka dot tree frog researchers thought it would, the amphibians still glowed as a result of the molecules hyloin-L1, hyloin-L2, and hyloin-G1. These are present in the animal’s lymph tissue, skin, and glandular secretions, giving them their distinct glow.
The team made the discovery by shining black lights on the frogs and seeing how they glowed.
“For some things we were planning on doing, we had to illuminate the frog tissues with UV light,” said study co-author Julián Faivovich, a researcher at the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires, Argentina, according to New Scientist. “Then we realized the whole frog was fluorescing.”
The newly found molecules are unique because they are not found anywhere else in the animal kingdom. In addition, they provide roughly 18 percent as much light as the full moon. This means the frogs may be able to use their glow to see in murky environments. To study this, the team plans to analyze the polka dot tree frog’s visual system to determine if they can see their own light.
They also plan to look for fluorescence in the 250 other tree frog species that have translucent skin like the polka dot tree frog. This could give more insight into the process and help scientists better understand why it evolved in some species but not others.
“I think it’s exciting,” said David Gruber a researcher at Baruch College, who was not involved in the research, according to Nature.com. “It opens up many more questions than are answered.”