Scientists have discovered the world's first fluorescent frog by accident while studying the pigment of polka-dot tree frogs found in the forests of Amazon basin.
The South American polka dotted tree frog (Hypsiboas punctatus) appears to have dull browny-green skin dotted with red spots under normal light but herpetologist Carlos Taboada, from the University of Buenos Aires in Argentina, and colleagues found that it gives off a greenish-blue glow under ultraviolet light and in dim settings.
Bioluminescent Versus Biofluorescence
Unlike in bioluminescent creatures whose light is produced by chemical reactions in their bodies, no chemical reaction occurs in biofluorescent organisms. Instead of giving off light from their own power source, these organisms typically absorb light at short wavelengths, transform it and then re-emit this at longer wavelengths as a different color.
Biofluorescent light in animals can be produced and only becomes visible to humans when the fluorescent organism gets illuminated by external sources such as a UV light bulb.
Fluorescence is more common in marine creatures such as sharks, fish, corals and is also found in the hawksbill turtle but it is rare in land animals having only previously known in parrots and in some scorpions.
Prior to the discovery, biofluorescence in frogs is unheard of. The South American tree frog that Taboada and colleagues studied is the first amphibian discovered to fluoresce.
Why Some Organisms Fluoresce
It is not clear why some organisms have the special ability to glow in ultraviolet light albeit scientists have theories which include mate attraction, camouflage, and communication.
For the South American fluorescent frogs, researchers suspect their fluorescence is relevant to visual perception. The amphibian's fluorescent molecules give off about 18 percent as much visible light as a full moon which is enough for related frog species to see by.
Researchers want to conduct a further study of the photoreceptors found in the frog's eyes to determine if the amphibians use their fluorescence for better vision at night.
"In low-light conditions, fluorescence accounts for an important fraction of the total emerging light, largely enhancing brightness of the individuals and matching the sensitivity of night vision in amphibians," the researchers wrote in their study published in journal PNAS. "These results introduce an unprecedented source of pigmentation in amphibians and highlight the potential relevance of fluorescence in visual perception in terrestrial environments."
Fluorescence In Marine Organisms
Fluorescence in marine organisms serves different purposes. Fluorescent pigment in shallow water corals acts as sunblock for the organisms as the intense ray of the sun that can cause sunburn to swimmers causes similar damage to corals and the symbiotic algae that live inside them.
Scientists also found fluorescence in deep-sea corals. They think that fluorescent pigments in corals that live in deeper waters help produce more light for their symbiotic algae that need it for photosynthesis.
A newly-found fluorescent species of polyps in the Red Sea is suspected of using its glow around its mouth to attract prey. The fluorescent flashlights can be seen by other invertebrates at sunset, sunrise and in the moonlight.