Amphibians are half-landlubbers, half water-babies. They breathe through skin that is moist, warty, crested and in some cases, poisonous or hallucinogenic. Some wear dull, leaflike-camo patterns. Others sport Guy Fieri flames.
And as cute, gross, pretty, ugly, magical and witchy-named as these slip-sliding creatures may be, they’ve been hiding something in a secret, fluorescent world invisible to humans. Many amphibians, whether salamanders, frogs or their distant cousins — possibly all of them — glow, according to a survey published Thursday in Scientific Reports.
“There is still a lot out there that we don’t know,” said Jennifer Lamb, a biologist who conducted the research with Matt Davis, both at St. Cloud State University in Minnesota. “This opens up this whole window into the possibility that organisms that can see fluorescence — their world may look a lot different from ours.”
The study paves the way for new research into how or why amphibians possess this special adaptation, which has potential applications in medical technology and conservation.
Science has documented many biofluorescent animals including chameleons, corals, jellyfish, reef fish, sharks, scorpions, butterflies, budgies, parrots, penguins, puffins, sea turtles and even flying squirrels. But scientists have focused more on aquatic animals, and when testing terrestrial animals, mainly used UV light (like in the sun). But in some patches of forest and freshwater habitats where amphibians live, blue light can dominate just as it does in deep water. Could this be why so few amphibians were known to fluoresce?
To find out, the St. Cloud team grabbed a blue-light flashlight and cast it on salamanders they were already studying.
As they watched those babies glow green through filtered lenses, they wondered: How many other amphibians would also ignite?
They schlepped their tools from the lab to the field as well as Chicago’s Shedd Aquarium.
“That was a lot of fun,” Dr. Lamb said. “Basically a bunch of scientists running around after dark in an aquarium with a lot of bright lights and fancy goggles.”
They tested animals from eight of 10 families of salamanders, five families of frogs and one family of caecilians, a type of limbless amphibian you might mistake for a worm or snake.
Every animal tested, even larvae, lit up in varying patterns and intensities. Spots, blotches, stripes, snotty secretions, urine and even bones and digits glowed after exposure to blue light. For most species this glow was bright green, but some produced yellow or orange fluorescence. Salamanders and caecilians without bold or brightly-colored patterns made up for it with unexpected lights: Their cloacal regions (multipurpose organs they use to eat, excrete and reproduce) shone bright as a flashlight.
That distantly related species of amphibians all fluoresced suggests that the trait likely developed early in amphibian evolution and may be quite widespread among the group. But what causes it and what purpose it serves remains a mystery.
In other animals, pigmentation, minerals, proteins and even a body part’s structure can create biofluorescence. It may aid in communication, predator evasion or visibility for members of the same species. Dr. Lamb plans to test these ideas out in the tiger salamander, the species she specializes in studying.
Amphibians’ secret light shows may lead to important medical advances. The discovery and development of green fluorescent protein, for instance, first isolated from a jellyfish, won a Nobel Prize in Chemistry in 2008 and is now common in medical and experimental imaging.
And as amphibians decline worldwide, difficulty finding them among dense vegetation and leaf litter, especially at night, makes tracking them for conservation tough. But knowing a tiny amphibian might shine green among leaves that fluoresce red in blue light, could make surveys much easier.
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