Under normal light, the South American polka dot tree frog (Hypsiboas punctatus) sports a muted palette of greens, yellows and reds. But dim the lights and switch on ultraviolet illumination, and this little amphibian gives off a bright blue and green glow.
The ability to absorb light at short wavelengths and re-emit it at longer wavelengths is called fluorescence, and is rare in terrestrial animals. Until now, it was unheard of in amphibians. Researchers also report that the polka dot tree frog uses fluorescent molecules totally unlike those found in other animals. The team published the find on 13 March in Proceedings of the National Academy of Sciences1.
Because fluorescence requires the absorption of light, it doesn’t happen in total darkness. That makes it distinct from bioluminescence, in which organisms give off their own light generated through chemical reactions. Many ocean creatures fluoresce, including corals, fish, sharks and one species of sea turtle (the hawksbill turtle, Eretmochelys imbricata). On land, fluorescence was previously known only in parrots and some scorpions. It is unclear why animals have this ability, although explanations include communication, camouflage and mate attraction.