Researchers from Duke University have identified a remarkable behavior in glass frogs during sleep. These tropical amphibians raise their transparency by briefly storing red blood cells in their liver, a strategy that likely aids camouflage while the animals rest on the leaves they inhabit. This discovery comes from a peer-reviewed study published in a respected scientific journal.
Hyalinobatrachium fleischmanni, a species known for skin that appears nearly see-through, spends daytime hours in slumber. With their delicate translucence, they blend into the leafy backdrop, making it harder for predators to spot them. The researchers used color photography to gauge how transparent the frogs became and advanced imaging techniques to trace red blood cell movement within living animals. The findings show that sleep increases transparency by a substantial margin, ranging from about one-third to a little over half of the frog’s normal opacity.
During deep rest, the frogs slash the circulating red blood cells by roughly 89 percent and temporarily withdraw them into the liver. This redistribution occurs without causing harm to the blood vessels or the body’s metabolism. As the frogs awaken and engage in activity, the red blood cell count in circulation rises again, restoring their usual appearance.
Although the exact mechanism behind red blood cell redistribution remains uncertain, scientists are pursuing clues about how this process is controlled. It is unclear whether glass frogs could become transparent again while a predator is nearby, and it is worth noting that in most vertebrates, a high concentration of red blood cells can contribute to arterial issues. Discovering an adaptation that prevents such problems could inspire new directions in cardiovascular medicine, including the development of safer anticoagulants or related therapies.