Some frogs found in South and Central America have the rare ability to turn their almost transparent appearance on and off, researchers report Thursday in the journal Science.
During the day, these nocturnal frogs sleep by hanging out under tree leaves. Their delicate, greenish transparent forms do not cast shadows, making them almost invisible to birds and other predators passing above or below.
But when northern glass frogs wake up and jump around in search of insects and mates, they turn an opaque maroon color.
“When they’re transparent, it’s for their safety,” said Junjie Yao, a biomedical engineer at Duke University and study co-author. When they are awake, they can actively avoid predators, but when they are asleep and are most vulnerable, “they have adapted to remain hidden.”
Using light and ultrasound technology, the researchers discovered the secret: While they sleep, the frogs concentrate, or “hide”, almost 90% of their red blood cells in their livers.
Because they have transparent skin and other tissues, it is the blood that circulates through their bodies that would otherwise give them away. The frogs also shrink and pack up most of their internal organs, Yao said.
The research “beautifully explains” how “glass frogs hide blood in their livers to maintain transparency,” said Juan Manuel Guayasamin, a frog biologist at the University San Francisco in 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 very little oxygen in the blood for several hours will be fatal. And concentrating the blood so tightly would lead to fatal clotting. But somehow the frogs survive.
Further research on the species could provide useful clues for the development of anti-clotting drugs, said Carlos Taboada, a Duke University biologist and co-author of the study.
Only a few animals, mostly sea dwellers, are naturally transparent, said Oxford University biologist Richard White, who was not involved in the study. “Openness 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 amounts of red blood through their bodies. The trick of hiding blood while sleeping seems to be unique to frogs.
“It’s just this really amazing, dynamic form of camouflage,” White said.
Citation: Glass act: Scientists reveal secrets of frog transparency (2022, December 25) Retrieved December 25, 2022, from https://phys.org/news/2022-12-glass-scientists-reveal-secrets-frog.html
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