“The Fluorescent Frog” sounds like a cool name for a bar (dibs!), but it's actually a real-life glowing amphibian.
Scientists were studying the pigment of the polka-dot tree frog in an Argentinean forest. Some parts of their research required them to shine a UVA or black light on the frogs. That was when they made the exciting new discovery.
Fluorescence is not a common trait in land animals. Scientists have previously observed fluorescence in marine animals like fish, shrimp, jellyfish, and coral. Some land organisms also display fluorescence, namely swallowtail butterflies, parrots, spiders, scorpions, and some plants. The polka-dot tree frog is the first known amphibian with natural fluorescence.
The fluorescent frog is about 3 centimeters long and has mottled greenish skin with red spots. The researchers actually expected to see the frogs glow a dull red because the frogs had a pigment called biliverdin. Biliverdin causes skin tissues to have a green color and emits a dull red glow.
Instead, the frogs glowed a bright green-blue, which was thoroughly surprising. “We couldn’t believe it,” says Julián Faivovich, one of the researchers. Because biliverdin doesn't cause organisms to have a greenish-blue glow, something else might be behind the fluorescence in tree frogs.
The polka-dot tree frog is a special discovery partly because it was unexpected. Their fluorescence is caused by a compound that scientists didn't think existed in vertebrates. According to the study on the polka-dot tree frog, the researchers found the molecules hyloin-L1, hyloin-L2 and hyloin-G1 in the frogs' skin tissue. Some fluorescent plants contain similar molecules and molecular structures.
The researchers discovered that the fluorescence of the frogs comes from their glands and lymph. The frogs glow 19% brighter on a full moon, and 30% brighter during twilight periods. It may also be possible that the frogs can see their own fluorescence. This is because the compound that causes fluorescence emits light at wavelengths that frogs are very sensitive to.
It's safe to assume that fluorescence serves some evolutionary purpose in the frogs. The researchers have figured out what causes the frogs' fluorescence, but they haven't figured out why the frogs glow. Some scientists expect that the fluorescence may have something to do with communication. After all, if the polka-dot tree frogs can see their own fluorescence, then other frogs might see it as well.
However, if there's anything that the fluorescent frog has taught us, it's to expect the unexpected.
There's one thing that we have to remember about frogs, though. Even though there are thousands of known frog species, they are all quite similar. This means that there may be other frog species out there that are also fluorescent.
This is another thing that makes this discovery quite exciting. More fluorescent frogs may be out there, just waiting for scientists to discover them. Faivovich in particular plans on studying 250 other tree frog species. It may be a good idea for scientists with a special interest in frogs to test their specimen for fluorescence.
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