Animals increase their transparency by accumulating red blood cells without harmful consequences
When tiny glass frogs hibernate for the day, they remove nearly 90 percent of their red blood cells from their circulation.
Colorful cells accumulate in hidden pockets inside the frog’s liver that mask the cells behind a mirror-like surface, a new study has found. Biologists know that glass frogs have translucent skin, but the temporary concealment of oily red blood puts a new twist on vertebrate camouflage.
“The heart stopped pumping red blood, which is the normal color of blood, and only pumped blue fluid,” says evolutionary biochemist Carlos Taboada of Duke University, one of the pioneers of hidden blood.
What may be even more surprising to humans — prone to blood clots — is that frogs keep almost all of their red blood cells collected for hours without blood clots, says one of the pioneers, Jesse Delia, who now works at the American Museum of Nature. . History in New York. Wake up the frog and the cells will simply unpack and start circulating again.
Hiding these erythrocytes can double or triple the transparency of glass frogs Taboada, Delia, and their colleagues report in Science from December 23. This greenish transparency can be of great importance to the snack-sized frogs, which spend the day hiding like little shadows on the undersides of leaves high in the forest canopy.
What made Delia think about transparency was an emergency photo. He studied the behavior of glass frogs, but he had never even seen them sleep. “They go to bed, I go to bed — that’s been my life for years,” he says. However, when he needed some charismatic portraits, he put some frogs in a laboratory dish and finally saw the animals sleep all day.
“It was really obvious that I wasn’t seeing red blood in my circulatory system,” says Delia. “I made that video — it was crazy.”
When he presented his project to the Duke University lab for support, he was stunned to learn that another young researcher had proposed to the same lab to study the transparency of glass frogs. “I was like, oh man,” Delia says. But the head of the Biological Optics Laboratory at Duke, Sönke Johnsen, told Delia and his rival Taboada that they have different skill sets and should solve the problem together. “I think we were strong-minded at first,” says Delia. “Now I consider him family.”
The past is prologue
To show what erythrocytes do in living frogs, they put together a complex puzzle. Light microscopy will not help to see through the specular outer tissue of the liver. Nothing that woke the frogs ( Hyalinobatrachium fleischmanni ), will also not work, because the erythrocytes will be thrown out through the body. Even anesthetizing the frogs didn’t allow the liver trick to work.
The answer, Delia and Taboada found, comes from a photoacoustic imaging technique primarily used by engineers. It reveals hidden innards through subtle vibrations created by light striking various molecules and causing small releases of energy. Junjie Yao of Duke joined the glass frog team to adapt the technique to frog liver, taking extra care not to wake the animals during the process.
When animals wake up, their blood returns (second clip)
Despite the glass frog’s name, transparency among vertebrates can be much greater, says fish biologist Sarah Friedman of the National Oceanic and Atmospheric Administration’s Alaska Fisheries Science Center in Seattle. In June she posted the image on Twitter freshly caught snail with spots ( Crystallichthys cyclospilus ), most of whose body was clear enough to see the flesh tones and finger lines on her hand as she held it. And this is not even the best example. The larval stages of tarpon and eels, glassfish and a species of Asian glass catfish are “almost perfectly transparent,” says Friedman, who was not involved in the new study.
But the advantage of these wonders is that they live in water, she says. The evolution of exquisite vitrification is easier when there is not such a stark visual difference between the bodies of animals and their aquatic homes. Still, having a transparent body is very cool, on land or at sea.
