Scientists Discover First Fluorescent Frog

The polka dot tree frog (Hypsiboas punctatus) glows under a blacklight, due to the presence of three fluorescent molecules in its lymph tissue and skin. 

By | March 15, 2017

JULIÁN FAIVOVICHA AND CARLOS TABOADA

When researchers placed a polka dot tree frog (Hypsiboas punctatus) under a black light, they made an unexpected discovery. The amphibian glowed with a bright, green-blue hue, the scientists reported Monday (March 13) in PNAS.

Fluorescence exists elsewhere in the animal kingdom, in some fish, sharks, and scorpions, for example. However, this is the first amphibian scientists have discovered with this trait. “We couldn’t believe it,” study co-author Julián Faivovich, a herpetologist at the University of Buenos Aires, told Nature.

Polka dog frogs contain biliverdin, a pigment found in some insects that gives them a dim red fluorescence, coauthor Carlos Taboada, a University of Buenos Aires herpetologist, told Nature. So the team expected the frogs to glow red under a UV flashlight, but instead, they emitted a brilliant, green-blue glow. The team also discovered that the fluorescence originated from three molecules, hyloin-L1, hyloin-L2 and hyloin-G1, in the frogs’ lymph tissue and skin.

“It would be interesting to investigate if [fluorescence] has a role in species recognition, or whether it facilitates the formation of couples,” Bibiana Rojas, an ecologist at the University of Jyväskylä, Finland, who was not involved in the work, told Chemistry World. “Fluorescence would be potentially very useful in a noisy environment and in a habitat with dense foliage, as it would make individuals brighter.”

It’s possible that other frog species are fluorescent, too. “Maybe we should be looking at every species we catch and trying to see if they fluoresce,” David Blackburn at the University of Florida who was not involved in the study, told New Scientist. “There’s very few frogs that have a feature that’s not found in any other frogs.” 

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Avatar of: JonRichfield

JonRichfield

Posts: 122

March 15, 2017

That the frogs are fluorescent I do not doubt, but I don't credit a syllable of any speculations to the effect that the fluorescence is of any importance to the animals, either for signalling or illumination or anything of the type.

Frogs and scorpions do not in nature have people shining UV torches at them, and in sunlight the fluorescence barely shows, except POSSIBLY to give a faint, subtle alteration to the impression that their skin colour conveys in bright light, rather like some commercial clothing detergent's fluorescent additives.

This is especially so under foliage or in burrows, where scorpions and frogs etc spend much of their time, and where UV intensity (and therefore fluorescence)  is negligible. At night the UV intensity is even lower than that of visible light, so the illumination by fluorescence is lower still.

In these matters it is crucially important, and highly instructive,  to distinguish between the nature and function of  fluorescence and bioluminescence. Consider deep-sea fishes, bacterial cultures on cold meat, and certain beetles such as some Elateridae and Lampyridae; they provide elaborate and functional examples and suggest no function for fluorescence at all.

There are two likely explanations for batracian and arachnid fluorescence that I can think of, and neither has to do with the value of the fluorescence to the animal; the simpler is that compounds such as biliverdin might happen to have other functions, and their fluorescence is a a physico-chemical accident of no selective or functional importance. Some compounds just happen to be fluorescent, and that is that.

Surprise...

The other is that the fluorescence is part of a protective mechanism whereby the compounds absorb UV, converting it to harmless visible light or even to near IR. The light emitted then is as adventitious as the logodaedaly of R. P. Lister's "defenestration", and the chemical compounds amount to sunblock.

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