https://www.the-scientist.com/news-opinion/glowing-amphibians-extremely-common-67204
ABOVE: Pseudobranchus striatus (left) and Icthyosaura alpestris (dorsal at center, ventral at right) as seen in natural light (top) and fluorescing under blue light (bottom)
© JENNIFER LAMB AND MATTHEW DAVIS
A study of the animals using blue light reveals what humans are not able to see with the naked eye.
Dozens of salamanders and other amphibians are biofluorescent under blue light, according to a study published Thursday (February 27) in Scientific Reports. On land, blue light is common after the sun has set, which may explain why amphibians, particularly nocturnal ones, react to it.
Many land animals, such as penguins, some rodents, and some amphibians, are known to fluoresce under ultraviolet light (360–380 nm), but most species known to fluoresce under blue light (440–460 nm) are strictly aquatic animals such as fish and turtles, as that is the wavelength of light that cuts through water the most.
Two biologists from St. Cloud State University, Jennifer Lamb and Matthew Davis, had decided to expose salamanders they were studying to blue light and found that they lit up. To understand how widespread the trait may be, the team was granted access to the Shedd Aquarium in Chicago. Using a flashlight that shone blue light, they analyzed eight salamander families, five frog families, and one family of caecilians, which are limbless amphibians. They found that across the board, all of the animals glowed.
A. opacum (left) fluoresces from its bones, especially in the digits and cloacal area, while A. tigrinum (right) glows brightly from the same places on its skin that are brightly-colored in the visible spectrum of light.
© JENNIFER LAMB AND MATTHEW DAVIS
“That was a lot of fun,” Lamb tells The New York Times. “Basically a bunch of scientists running around after dark in an aquarium with a lot of bright lights and fancy goggles.”
Many of the animals lit up with a brilliant green, though some appeared more yellow. Some fluoresced from mucous discharge, urine, or, in the case of a few species, such as the marbled salamander (Ambystoma opacum), a faint glow actually came from the bones.
“There is still a lot out there that we don’t know,” Lamb tells the Times. “This opens up this whole window into the possibility that organisms that can see fluorescence—their world may look a lot different from ours.”
Because the trait is so widespread, it might have evolved early on in amphibians’ history. The exact function of this glowing has not been confirmed. The team hypothesizes in the paper that it could range from “communication, sexual selection, camouflage, and improved visual acuity to perhaps no function at all in some lineages.”
There were variations of fluorescent patterning due to sex and age of the animal, they found.
“In some species, we do see differences in color patterns between males and females, so it could be related to reproduction,” Lamb explains to New Scientist. “In the loudness of a frog chorus, with hundreds calling at once, perhaps females could use the light to find a specific male when the audio signals aren’t helpful.”
The team also suggests that a better understanding of this process might help amphibian conservation efforts. Amphibians around the world are losing numbers rapidly due to habitat destruction, climate change, and a devastating chytrid fungus that has already factored into the extinction of 90 amphibious species.
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