The polka-dot tree frog (Hypsiboas punctatus) is usually the color of bright green with a smattering of reds and a bit of yellow. However, researchers recently discovered that this particular species of frog glows fluorescent in dim light, glowing a bright blue and green. The researchers also found that the polka-dot tree frog used fluorescent molecules differently than any other animal. This fluorescence trait is rare among land animals and unheard of within the amphibian world.
The polka-dot tree frog can be found in areas that are subtropical or tropical dry or moist forests, lowland forests, subtropical or tropical swamps, moist montane forests, freshwater marshes, rural gardens, urban areas, and degraded former forests. They can be found in countries such as Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, and Venezuela. The International Union for Conservation of Nature does not consider them threatened.
Scientific American reported that many terrestrial animals are not fluorescent, with the exceptions being parrots and some scorpions while many ocean animals are fluorescent including fish, corals, and one species of sea turtle. Fluorescence needs light to occur and is different from bioluminescence where organisms generate light through “chemical reactions.”
The team of South American researchers theorized that frogs might have a red fluorescence due to the pigment biliverdin, which can turn amphibian tissues and bone green. Biliverdin in the polka-dot tree frog does not. Carlos Taboada, one of the authors of the study and a herpetologist at the University of Buenos Aires in Argentina, used a blacklight or a UVA flashlight on the polka-dot tree frogs they collected in Argentina. Instead of giving off the expected reddish color from the biliverdin, the polka-dot tree frogs glowed a greenish-blue color. The Christian Science Monitor stated that the research team was surprised by the finding and “were not expecting” this to happen, said Norberto Peporine Lopes, co-author, and University of São Paulo chemist.
The researchers found that specific molecules (hyloin G1, hyloin-L1, and hyloin-L2) gave the polka-dot tree frogs their distinct fluorescence. The particles were found in the skin, lymph tissue, and glandular secretions and contained a chain of hydrocarbons that is associated with fluorescent molecules in animals. Lopes stated that the “closest similar molecules are found in plants.”
The study went on to say that the polka-dot tree frogs emitted an amount of light that was surprising. Because science does not know how this affects the frog’s eyesight, Taboada and company plan on further studies including the purpose of the molecules. The study findings were published in the journal Proceedings of the National Academy of Science.
By Cheryl Werber