Now you see them, now you don’t. Some frogs found in South and Central America have the rare ability to turn on and off their nearly transparent appearance, researchers report Thursday 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.
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, a Duke University biomedical engineer and study coauthor.
Using light and ultrasound imaging technology, the researchers discovered the secret: While asleep, the frogs concentrate, or “hide,” nearly 90% of their red blood cells in their liver. Because they have transparent skin and other tissues, it’s the blood circulating through their bodies that otherwise would give them away. — The Associated Press