The mystery of why glass frogs have see-through skin has been solved, scientists say: the unusual feature is a type of camouflage. The Guardian reports: Glass frogs are found in tropical Central and South America, and get their name from their skin. However, the frogs are not truly transparent but translucent, with the skin on their backs typically a vivid green and their intestines and heart visible through their underbelly. This has led to a question that has kept scientists on the hop. "If predators cannot see straight though the frogs, why do glass frogs have transparent skin at all, and not the opaque camouflaged patterns of other tree frog species?" said Dr James Barnett, a postdoctoral researcher at McMaster University, Canada, who co-authored the study. Barnett and colleagues say they have cracked the conundrum. "The frog is always green to generally match leaves, but leaves will differ in their brightness," said Barnett. The team say that while the color of the frog's body changes little against dark or light foliage, the legs are more translucent and hence shift in brightness, helping the amphibians to blend in. "By having translucent legs and resting with the legs surrounding the body, the frog's edge is transformed into a softer, less contrasting gradient from the leaf to the legs, and again from the legs to the body," said Barnett, noting that this makes the frog's outline less recognizable to predators. Writing in the U.S. journal Proceedings of the National Academy of Sciences, Barnett and colleagues report how they carried out three experiments.

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