Study Reveals How Glass Frogs Become Transparent

Glass frogs activate their invisibility cloaks by hiding nearly all their red blood cells in the liver while sleeping, according to a study published on Thursday. 

Studying the paperclip-sized amphibians — known for their see-through chest and belly region — could have a major impact on human medicine as well.

What did researchers find?

The group of scientists at the Duke University in the US state of North Carolina conducted the research on the frogs, which are native to Central and South America.

According to findings published in the journal Science, researchers brought several glass frogs into their labs and used highly calibrated cameras to study the small amphibians.

They discovered that the frogs remain opaque at night when they generally feed and breed. 

A glass frog's beating heart and other organs are visible through its transparent chest and bellyImage: Jesse Delia/AMNH via AP/picture alliance

However, they hide most of their rust-colored red blood cells in the liver during the day to help them camouflage — appearing like dew drops on the green leaves they rest on — to protect themselves from predators. 

Livers of these frogs swell up to 40% in size to hide 89% of their blood while sleeping, researchers reported in Science.

That's drastically higher than tree frogs which can only store 12% of their blood in the organ, according to a Science press article on the research.

Transparency in nature is largely seen in aquatic beings such as eel larvae or jellyfish.

Animals that live on land, partly or full-time, do not hold this superpower given light reflects differently through air than water. Red blood cells also get their crimson because the protein in the hemoglobin absorbs light.

Glass frogs can hide nearly 90% of their blood in the liver while they sleep, researchers foundImage: Jesse Delia/AMNH via AP/picture alliance

Glass frogs seem to have crossed that hurdle. The study found that the cold-blooded animals became 34% to 61% more transparent while they were resting than when active. Once the frogs woke up, blood started pumping through their veins again, making them opaque.

What are the implications for humans?

What remains a mystery is how the glass frogs pull off their transparency trick without dying.

Experts explained that having such little blood flowing through the body for several hours at a stretch would be fatal for other animals because concentrating blood tightly in an organ would lead to deadly blood clots. Yet, the frogs survive.

Carlos Taboada, co-author of the study, told the Associated Press (AP) that further research on the terrestrial animal could lead to discovery of anti-blood clotting medications for humans.

Thrombosis is a leading cause of deaths globally, with one in four people dying because of blood clots or complications caused by blood clots.

The discovery takes researchers one step closer to finding treatments for potentially fatal clots.

"This seemingly basic observation about glass frogs leads to very clear implications for human health,” said Richard White, an oncologist at the University of Oxford who has separately studied translucent Zebrafish, told the AP.

This report was written in part with material from The Associated Press.

Edited by: Rebecca Staudenmaier