March 29 (UPI) -- While studying the mating calls of pumpkin toadlets in the Brazilian rainforest, biologists realized the tiny frogs were deaf to their own songs. Further investigation revealed an alternate mode of communication, glow-in-the-dark bones.
When scientists studied the miniature Brazilian frogs under an ultra-violet lamp, they found glowing patterns across the heads and backs of the tiny reptiles.
"The fluorescent patterns are only visible to the human eye under a UV lamp," Sandra Goutte, an evolutionary biologist and researcher at New York University Abu Dhabi, said in a news release. "In nature, if they were visible to other animals, they could be used as intra-specific communication signals or as reinforcement of their aposematic coloration, warning potential predators of their toxicity."
Back in the lab, Goutte and her colleagues compared the skeletons of pumpkin toadlets to the skeletons of related, non-fluorescent species. The bones of the pumpkin toadlets glowed under the UV lamp.
Pumpkin toadlets are active during the daytime. Scientists estimate sunlight's UV or near-UV wavelengths are sufficient to illuminate fluorescent patterns detectable by some species.
Researchers identified fluorescent dermal bones in the head and back of two pumpkin toad species, Brachycephalus ephippium and B. pitanga. They described their discovery in the journal Scientific Reports.
Scientists aren't yet sure whether the fluorescent patterns are used for intraspecies communication, to ward off specific predators or both.
"More research on the behavior of these frogs and their predators is needed to pinpoint the potential function of this unique luminescence," Goutte said.