A rare discovery in land animals revealed a new way of glowing.
Observe this polka dot tree frog fluoresce under the illumination of ultraviolet light.
In normal light, the Hypsiboas punctatus is draped in a soft palette of green, yellow and red. But let the light dim and turn on the ultraviolet light, and this small amphibian emits a bright blue-green light.
Being able to absorb light of short wavelengths and re-emit them at longer wavelengths is called fluorescence, which is rare in earthly organisms. The researchers also reported that polka dot tree frogs use fluorescent molecules quite differently from those found in other animals. The team published the findings in the Proceedings of the National Academy of Sciences on March 13.
Because fluorescence requires the absorption of light, it does not occur in complete darkness. This makes it different from the way organisms emit light, in which organisms emit their own light through chemical reactions. Many marine life fluorescence, including corals, fish, sharks and a species of turtle (eretmochelys imbricata). On land, parrots and some scorpions were previously known only to fluoresce. It's unclear why animals have this ability, although there are various explanations including communication, camouflage and attracting mates.
The researchers first thought that they might have found red fluorescence in these frogs because they contained a natural pigment called bilirubin. Normally, bilirubin turns the tissues and bones of amphibians green. In some insects, however, bilirubin-bound proteins glow reddish fluorescence, says Carlos Taboada, a herpetologist at the University of Buenos Aires in Argentina. But in the dot tree frog, bilirubin became inexplicable.
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When Taboada and his colleagues trained a polka dot tree frog collected from near Santa Fe, Argentina, with ultraviolet flashlights (or black light), they were surprised to find that the animal emitted a strong blue-green glow instead of a reddish glow. "We don't believe it," said study collaborator Julizán faivovich, a herpetologist who is also at the University of Buenos Aires.
Three molecules in the animal's lymphoid tissue, skin, and glandular secretions—hyloin-l1, hyloin-l2, and hyloin-g1—are responsible for the green fluorescence. The molecule contains a ring structure and chain hydrocarbons, which are unique among fluorescent molecules in known animals. The closest similar molecule was found in plants, said study collaborator Norberto Peporine Lopes, a chemist at the University of São Paulo in Brazil.
The newly described fluorescent molecule emits an astonishing amount of light, providing about 18 percent of the visible light of a full moon — enough for the frog species involved to see. Little is known about the dot tree frog's visual system and photoreceptor cells, so tabada plans to study these to determine if the frog can see its own fluorescence.
"I think it's exciting," says David Gruber, a marine biologist at the City University of New York at Baruch, who and his colleagues discovered fluorescence on hawksbill turtles in 2015 (reference 2). "It reveals far more questions than has been answered," he said — including the ecological and behavioral functions of fluorescence.
Faivovich wanted to look for fluorescence in 250 other species of tree frogs with translucent skin like the dot tree frog. He hopes he's not the only one: "I really hope that other colleagues will be very interested in this phenomenon and will bring ultraviolet flashlights to this field." He said.
Original from: http://www.nature.com/news/first-fluorescent-frog-found-1.21616