Scientists have discovered the secret of how frogs found in South and Central America have the ability to turn themselves almost transparent, according to a report in the journal Science.
During the day, these nocturnal frogs sleep by hanging underneath tree leaves. Their delicate, greenish transparent forms don’t cast shadows, rendering them almost invisible to birds and other predators passing overhead or underneath. But when northern glass frogs wake up and hop around in search of insects and mates, they take on an opaque reddish-brown color.
“When they’re transparent, it’s for their safety,” said Junjie Yao of Duke University. When they’re awake, they can easily evade predators, but when they’re sleeping and most vulnerable, “they have adapted to remain hidden.”
Using light and ultrasound, researchers discovered the secret.
While the frogs sleep they hide nearly 90% of their red blood cells in their livers.
Because they have transparent skin and other tissues, it’s the blood circulating through their bodies that would otherwise give them away.
Juan Manuel Guayasamin, a frog biologist at University San Francisco of Quito, Ecuador, said…
“The research beautifully explains how glass frogs conceal blood in the liver to maintain transparency.”
Exactly how they do this, and why it doesn’t kill them, remains a mystery. For most animals, having very little blood circulating oxygen for several hours would be deadly. And concentrating blood so tightly would result in fatal clotting. But somehow, the frogs survive.
Further research on the species could provide useful clues for the development of anti-blood clotting medications, said Carlos Taboada of Duke University.
Only a few animals, mostly ocean dwellers, are naturally transparent. Oxford University biologist Richard White. said…
“Transparency is super rare in nature, and in land animals, it’s essentially unheard of outside of the glass frog,” White said.
Those that are transparent include some fish, shrimp, jellyfish, worms and insects — none of which move large quantities of red blood through their bodies. The trick of hiding blood while sleeping appears to be unique to the frogs.
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