Of all the world’s amphibians — some 7,600 species — none had been confirmed to exhibit fluorescence, until now.
Scientists in Argentina and Brazil say they’ve found the first solid evidence of a fluorescent amphibian, courtesy of the South American tree frog.
Their findings, published Monday in the Proceedings of the National Academy of Sciences, offer clues into how this tiny tree frog survives in its environment. The study may also spur more research into fluorescence on land, a largely unexplored area within visual ecology.
Unlike in the depths of the ocean, where fluorescent fish and plants stand out, the terrestrial environment has far more competition among colors. That kaleidoscope can make it harder for scientists to spot fluorescence in nature, or know where it exists, said Carlos Taboada, the study’s lead author and a biologist at the University of Buenos Aires.
“We had a suspicion that this [frog] species could be fluorescent,” he said. “What was really shocking was the intensity and color of fluorescence, which we didn’t expect at all.”
Fluorescence is a physical-chemical phenomenon in which short-wavelength electromagnetic radiation — a.k.a. light — is absorbed and then reemitted at longer wavelengths. For an organism to be fluorescent, it must have fluorophores, the chemical compounds that can reemit light.
This is different than a creature simply looking neon, or appearing to glow, which can happen with coloration and may explain earlier reports of glow-in-the-dark amphibians. In coloration, light interacts with the molecules on a surface, and that light is then reemitted at the same wavelength.
The Hypsiboas punctatus tree frog has skin so translucent that you can see its internal organs. Taboada said he and his colleagues thought the nearly clear skin would give them a better view of how the skin interacts with light.
The team is still studying how and why the tree frog uses its fluorescence at night and twilight. But they have a hypothesis: frogs might glow brighter to make themselves more visible to one another.
Researchers noticed that frogs begin fluorescing, and increase the brightness of their fluorescence, when they saw other frogs. The nocturnal frogs have two retinal photo-receptors that are less sensitive to certain wavelengths of light. But the receptors are more sensitive to longer wavelengths, which the frogs produce with fluorescence.
“This shows fluorescence may be relevant, even in terrestrial environments,” he said by phone from Buenos Aires. “It opens many new research pathways.”