Scientists reveal the secrets of transparency in frogs

WASHINGTON (AP) — Now you see them, now you don’t.

Some frogs found in South and Central America have the rare ability to turn their nearly transparent appearance on and off, researchers report Thursday in the journal Science.

During the day, these nocturnal frogs sleep hanging under the leaves of trees. Their delicate, greenish, transparent shapes cast no shadows, making them nearly invisible to birds and other predators passing above or below.

But when northern glass frogs wake up and hop around in search of insects and mates, they turn a dull reddish-brown color.

“When they’re transparent, it’s for their safety,” said Junjie Yao, a biomedical engineer at Duke University and co-author of the study. When awake, they can actively evade predators, but when they are asleep and at their most vulnerable, they have “adapted to staying hidden.”

Using light and ultrasound imaging technology, researchers have uncovered the secret: While they sleep, frogs concentrate, or “hide,” nearly 90 percent of their red blood cells in their livers.

Because they have transparent skin and other tissue, it is the blood circulating in their bodies that would otherwise give them away. Frogs also shrink and pack on most of their internal organs, Yao said.

The research “beautifully explains” how “glass frogs hide their blood in their livers to maintain its transparency,” said Juan Manuel Guayasamin, a frog biologist at San Francisco University in Quito, Ecuador, who was not involved in the study. study.

Exactly how they do it, and why it doesn’t kill them, remains a mystery. For most animals, having very little oxygen circulating in their blood for several hours would be deadly. And concentrating the blood so tightly would result in fatal clotting. But somehow, the frogs survive.

Further research on the species could provide clues for the development of anti-blood-clotting drugs, said Carlos Taboada, a biologist at Duke University and co-author of the study.

Only a few animals, mostly ocean dwellers, are naturally transparent, said University of Oxford biologist Richard White, who was not involved in the study. “Transparency is super rare in nature, and in land animals, it’s essentially unknown outside of the glass frog,” White said.

Those that are transparent include some fish, shrimp, jellyfish, worms, and insects, none of which move large amounts of red blood through their bodies. The trick of hiding blood while sleeping appears to be unique to frogs.

“It’s just this really amazing and dynamic form of camouflage,” White said.

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The Associated Press Health and Science Department receives support from the Science and Educational Media Group of the Howard Hughes Medical Institute. The AP is solely responsible for all content.

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