At first glance, you might miss the glass frog of the Costa Rican rainforest. As the name suggests, it’s almost transparent. Aside from a lime green streak on its back, its skin, muscles, and other tissues are all see-through. Then there are its tiny organs, which seem to float in this translucent flesh, like a pale fruit cocktail in the weirdest Jell-O salad ever adorned a tree branch.
Translucent can be useful as to evade predators, which is rare in terrestrial animals. Their bodies are filled with substances that light cannot penetrate, many of which are necessary for life. Glass frogs seem to have evolved transparent versions of some of these anatomical features, but they also have some tricks up their sleeve to mask the residual color when they’re most vulnerable.
In a study published in Science magazine on Thursday, researchers report that when a glass frog goes to sleep, nearly all of its red blood cells withdraw to the liver. They hide in the organ and allow the frog to be nearly invisible when it rests. In addition to revealing another remarkable adaptation in nature, the discovery could lead to clues on how to prevent deadly blood clots.
Like humans, glass frogs rely on hemoglobin, a colored protein in red blood cells that carries oxygen throughout the body. Jesse Delia and Carlos Taboada, biologists and authors of the new paper, spent a lot of time observing frogs when they realized that sometimes, that red color seemed to disappear.
Dr Delia, who works at the American Museum of Natural History in New York, said: ‘When they are awake, the circulatory system is red. “When they’re sleeping, they’re not.”
Where did the red cells go?
To solve the mystery of the disappearance of blood cells, researchers and their colleagues wanted to photograph frogs under anesthesia — when blood cells were clearly visible in circulation. in their bodies — and sleeping, when these cells are not visible. To do that, they needed to find a way to look inside the frog’s organs, which have a mirror-like appearance that helps the frogs blend in. Dr. Taboada, a researcher at Duke University, said they suspect blood will withdraw to various organs when not circulating.
The researchers ultimately relied not on light but on sound to show them what was inside. They stimulated molecules inside the vesicle to release ultrasonic waves, which can be used to determine the contents.
As soon as they compared images of frogs sleeping and anesthetized, a big difference emerged.
“All the signals come from the liver,” says Dr. Taboada. About 89% of the frog’s red blood cells have already accumulated in that organ.
That makes sense: The liver, which filters the blood, is the logical destination for red blood cells, he says.
What’s strange and what researchers still don’t understand is how the frogs were able to cram all these cells together without dying from a blood clot. In most vertebrates, when blood cells collide, blood clots. The resulting clot can scab to seal a wound — or, if the clot is in a blood vessel, it can clog the circulatory system and kill the organism. In the United States of America, According to the Centers for Disease Control and PreventionUp to 100,000 people die from blood clots each year.
New research shows that glass frogs can control when blood clots. If injured, they will scab in the usual way. But when they were asleep, with red blood cells packed like sardines in their livers, no blood clots formed.
This finding implies that glass frogs could teach us something about how to prevent blood clots from forming in our own bodies. If future research can shed light on what keeps frogs safe, it could lead to treatments to reduce blood clot deaths in humans.
Immediately, the results raise other questions, the researchers say. If 89 percent of the oxygen-carrying cells are hidden in the liver while the frog sleeps, how does it breathe? They wondered if the frogs could switch their metabolism to a mode that requires almost no oxygen, perhaps similar to what other frogs do when they hibernate during the winter.
The paper is just the beginning of this line of research. The team improved their imaging techniques to scan frogs more quickly and reveal substances other than blood as they move around the creatures.
Dr Delia said in a phone interview: “We’re in the lab now. “Literally a frog is scanning the system. I have to go check it out.”