Some frogs found in South and Central America have the rare ability to turn their nearly transparent appearance on and off, researchers reported Thursday in the journal Science. (Jesse Delia, AMNH via Associated Press)
Estimated reading time: 2-3 minutes
WASHINGTON – 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, the researchers report Thursday in the journal. Sciences.
During the day, these nocturnal frogs sleep hanging under the leaves of the trees. Their delicate, transparent greenish 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 looking for insects and mates, they turn a dull reddish-brown color.
“When they’re transparent, it’s for your safety,” said Junjie Yao, a biomedical engineer at Duke University and a co-author of the study. When awake, they can actively evade predators, but when asleep and at their most vulnerable, they “have adapted to stay hidden.”
Using ultrasound and light imaging technology, the researchers discovered the secret: while sleeping, frogs concentrate, or “hide,” nearly 90% of their red blood cells in their livers.
Because they have transparent skin and other tissue, it is the blood that circulates through their bodies that would otherwise give them away. Frogs also shrink and pack most of their internal organs together, Yao said.
The research “beautifully explains” how “glass frogs hide blood in the liver to maintain transparency,” said Juan Manuel Guayasamin, a frog biologist at the Universidad San Francisco de Quito, Ecuador, who was not involved in the study.
Exactly how they do this, and why it doesn’t kill them, remains a mystery. For most animals, having too little oxygen circulating in the blood for several hours would be fatal. And concentrating the blood so strongly would result in fatal clotting. But somehow, the frogs survive.
Additional research on the species could provide useful clues for the development of blood-thinning 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 Oxford University biologist Richard White, who was not involved in the study. “Transparency is very rare in nature, and in terrestrial animals, it’s essentially unheard of outside of the glass frog,” White said.
The ones that are transparent include some. The trick of hiding blood while sleeping seems to be unique to frogs.
“It’s a really amazing and dynamic form of camouflage,” White said.
The Associated Press Department of Health and Science receives support from the Howard Hughes Medical Institute Science and Educational Media Group. The AP is solely responsible for all content.
