A group of glass frogs sleeping together upside down on a leaf, showing off their camouflage.
Jesse Delia
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Jesse Delia
A group of glass frogs sleeping together upside down on a leaf, showing off their camouflage.
Jesse Delia
Jesse Delia says it happened in Panama. A few years ago, he was finishing his fieldwork, a research project examining the behavior of the parents of a type of glass frog. He brought a handful of these transparent, half-dollar-sized frogs to the lab for a photo shoot.
It led to an exciting discovery.
“I wanted to get some photos of a nice glass frog belly,” Delia tells NPR. She placed them in a petri dish and saw each frog’s circulatory system through their translucent skin: “red with red blood cells.”
But when he returned later, the frogs were sleeping and the blood “had disappeared.”
It was as if the arteries and veins had melted. “I thought she was crazy,” recalls Delia, now a biologist at the American Museum of Natural History in New York.
He took a video of the glass frog’s beating heart and sent it to his longtime collaborator, Carlos Taboada, a biologist at Duke University.
“It was colorless,” says Taboada. Not even the telltale red streak of a glass was visible on the frog’s belly. “It was crazy. I’ve never seen anything like it.”
Both Delia and Taboada wanted to know: where did all the red blood from the frogs go?
In a new paper In the diary SciencesTaboada, Delia and their collaborators offer an answer: “They hide most of their red blood cells in the liver,” explains Delia.
The same glass frog photographed during sleep (left) and while active (right), showing the difference in red blood cell circulation.
Jesse Delia
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Jesse Delia
The same glass frog photographed during sleep (left) and while active (right), showing the difference in red blood cell circulation.
Jesse Delia
During the day, while glass frogs sleep on green leaves, they are vulnerable to predators, so they manage to camouflage themselves by becoming super transparent. (Their livers, among other organs, are coated in highly reflective white crystals.) Since their red blood cells carry very little oxygen, Delia says it’s likely that frogs have “some alternative process that allows them to keep their cells alive during transparency.” Then at night, when the frogs become active, “feeding and mating, going about their usual business,” the vitreous amphibians release their red blood cells back into circulation.
Taboada says that frogs “pack about 90% of their red blood cells into a very, very small volume. Normally, those conditions can trigger some bleeding disorders.” The researchers say knowing how glass frogs bypass a blood-clotting cascade could pave the way for new anticoagulants for humans.
