Glowing frogs and salamanders

Sharks do it, fish do it, even scorpions and spiders do it. Now, researchers have revealed more of nature’s secret light show: many different species of frogs and salamanders also do it.

These animals all glow under blue or ultraviolet light, a phenomenon known as biofluorescence. The higher energy wavelengths of light are absorbed and then reemitted as vivid fluorescent colours including greens, blues and reds at lower energy wavelengths.

Most previous research on biofluorescence has focussed on marine vertebrates or terrestrial invertebrates, like arthropods, explains lead author Jennifer Lamb from St Cloud in Minnesota, US.

Adding to that, recent work by her co-author Matthew Davis found it is widespread in many different types of marine animals including ray-finned fishes and cartilaginous fishes like sharks.

“That is what, in part, led us to wonder if biofluorescence might also occur in amphibians,” she says, having previously been observed in only one salamander and three frog species.

“We surveyed a few initial species of salamanders I was finding during some of my other research, like the Eastern Tiger Salamander, and found that they fluoresced brightly.”

This led them to start testing more amphibians, publishing their findings in the journal Scientific Reports.

They illuminated one to five individuals from 32 species with blue or ultraviolet light then viewed or photographed them through a long-pass filter, which only allows fluorescing light through, using spectrometry to measure the light wavelengths.

All the tested species of salamanders, frogs and caecilians glowed – mainly with green – although the patterns differed greatly, ranging from fluorescent blotches and stripes to fluorescent bones or all-over fluorescence.

“We were surprised that even species of salamanders with dull colours or patterns fluoresced,” says Lamb, “like the Rio Cauca caecilian or the three-toed amphiuma salamander.

“There is a lot of excitement in these new discoveries, and it helps drive home the point that there is still a lot to learn about many groups of organisms in nature.”

It seemed to occur across different life-history stages (tadpoles and adults) and in species from very different environments, and Lamb says there could be multiple mechanisms causing it, including pigments, compounds in mucus and minerals.

These could have been shaped by the different animals’ pattern of evolution.

“In some groups of organisms, like coral reef fishes, they might use biofluorescence for camouflage,” Lamb explains. “In others, like some birds, biofluorescence may be used to attract mates, or like in some arthropods, to communicate.

“It’s possible that amphibians may use biofluorescence in one or all of these ways, but those are some of the next steps for us and others to investigate.”