There are a wealth of biofluorescent creatures in the world from up in the trees, to under the seas, but not many people had considered whether it occurs much in amphibians. Now, a new study in Scientific Reports has revealed it is in fact much more widespread than we knew.
Biofluorescence – when an organism absorbs light, re-emitting it at a different wavelength (not to be confused with bioluminescence) – had only been observed in one species of salamander and three frog species before now. In the new study, Jennifer Lamb and Matthew Davis, assistant professor and associate professor of biology respectively at St Cloud State University, Minnesota tested 32 species of amphibians, including salamanders, newts, frogs, and caecilians and found biofluorescence occurred in all of them. They think, based on their initial study, it probably occurs in many more.
Previous research carried out by Davis and colleagues on fluorescence occurring in ray-finned fishes and cartilaginous sharks led Lamb to wonder about her own research subjects: salamanders. After testing an Eastern tiger salamander and discovering it did indeed glow brightly, they decided to explore further.
“Once we realized biofluoresence was widespread in salamanders, we began testing frogs and caecilians,” Lamb told IFLScience. “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.”
They tested between one and five individuals from the 32 species by exposing them to blue and ultra-violet light, then viewing and photographing them through a long-pass filter. This allows only the fluorescent light to come through, Lamb explained. They discovered that all the species they studied were biofluorescent, all emitting green light, though some were slightly more yellow. However, the patterns that fluoresced were very different among species; some were blotches, some stripes, some the whole body, and others just the bones.
“We suspect that the variation in biofluoresence among species is in part due to different mechanisms causing the fluorescence,” Lamb told IFLScience. “But some of the variations could be because species might use biofluoresence differently.”
Their findings suggest that causes of biofluorescence include fluorescent proteins or compounds in the skin, secretions like mucous, minerals in the bones, or even minerals in things like urine. Though they are unsure yet why amphibians evolved fluorescence, its evolution may also be linked to the mechanism causing it. Their eyes contain rod cells sensitive to green or blue light so it appears they are able to see the light being fluoresced. It's possible the light allows amphibians to see each other in low light settings, or help others detect and differentiate them from their environment.
“In some groups of organisms, like coral reef fishes, they might use biofluoresence for camouflage. In others, like some birds, biofluoresence may be used to attract mates, or like in some arthropods, to communicate,” Lamb said. “It's possible that amphibians may use biofluoresence in one or all of these ways, but those are some of the next steps for us and others to investigate.”