In the tropical rainforests of Central and South America lives the glassfrog (Hyalinobatrachium fleischmanni), a small tree-dwelling amphibian that takes camouflage to an unprecedented biological extreme. During the night it feeds and reproduces like any other frog, but when the sun rises it retreats to rest on the undersides of leaves, turning its body practically translucent to avoid casting shadows.
Achieving invisibility poses a critical physiological obstacle: even if the skin, bones, and muscles are transparent, the dense network of circulating red blood cells would inevitably tint the animal a reddish hue visible to any hungry bird. In 2022, a multidisciplinary team discovered the frog's unusual solution: upon falling asleep, it removes up to 89% of its red blood cells from circulation and packs them en masse inside its liver.
This organ, protected by a reflective membrane packed with guanine crystals, acts like a safe that doubles in size to house the compacted blood. What is truly revolutionary for medical science is that the frogs manage to pack such an excessive concentration of erythrocytes without suffering thrombosis or lethal blood clots. Upon waking, blood flow is restored within seconds in a completely normal fashion, a natural anticoagulant ability that researchers are already studying to prevent strokes and heart attacks in humans.
Source: Science (Taboada et al., 2022 - 'Glassfrogs conceal erythrocytes in the liver to maintain transparency')
