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The golden button (Brachycephalus ephippium) is a small, poisonous and brightly colored frog that lives in the Atlantic rainforests of Brazil. During the heat season, they can be seen and heard through the forest producing soft hums in search of a mate.

An international team of researchers, led by Sandra Goutte, was studying the acoustic communications of these frogs, when they discovered that they were not able to hear their own mating calls. Before this question, they looked for alternative visual signals that the amphibians could use to communicate. Unexpectedly, when they directed an ultraviolet (UV) lamp to their backs and heads, they shone brightly.

In a study published in Scientific Reports, Goutte's team points out that fluorescent pattern are created by bone plates located directly beneath very thin skin. In fact, the entire gold-button skeleton is highly fluorescent, but fluorescence is only visible when the layer of skin tissue over the bones is very thin. The lack of dark pigmented cells in the skin (which block the passage of light) and the thinness of the skin allow ultraviolet light to pass through them and stimulate the fluorescence of the bony plates of the skull.

"Fluorescent patterns are only visible to the human eye under a UV lamp - explains Goutte - In nature, if they were visible to other animals, they could be used as a specific communication signals or as reinforcement of their coloration, warning potential predators. However, more research is needed on the behavior of these frogs and their predators to identify the potential function of this unique luminescence. "