In the tropical forests of Latin America, a beating heart of amphibian diversity, a number of frogs wear shimmering colors. Red, orange, yellow, blue … way of recognizing yourself, seducing yourself, but above all to warn the predators of their toxicity. Please note, a mechant amphibian!
to escape appetites voracious, the approximately 158 species of glass frogs identified from Mexico in Venezuela have adopted another strategy. First, they only move at night, which reduces potential dangers. The day, they sleep, sheltered Leaves. Or more exactly, hidden on the leaves. Because there lies their originality: on the battery side, they display a stunning green color of similarity with the ambient vegetation; side side, they have a ventral transparency which erases their shadow on the sheet. Lying on the back, they become almost undetectable. This and there appear two black spots (eyes) or shadows (some organs, including the heart). But no silhouette capable of attracting birds, snakes or mammals.
“This camouflage technique is very common in the ocean, supports biologist Carlos Taboada, from Duke University in the United States. Just think of jellyfish. But we vertebrate are filled with pigments, glands , complex structures that absorb and disseminate light and make us opaque. “With colleagues from five American universities and museums, he published, on December 22, in the review Science , an article that reveals the underside of this invisibility cape.
Photoacoustic microscopes
The researchers have placed several specimens of hyalinobatrachety glass frogs Fleischmanni under the eye of photoacoustic microscopes. These devices, syntheses of microscopes and ultrasounds, record the ultrasound emitted by molecules excited by lasers. Carlos Taboada was able to track down red blood cells inside the day and night frogs. To his surprise, he discovered a so far unknown blood mechanism. Before going to bed, in the early morning, the frog migrates 90 % of the red blood cells from its blood to the liver, keeping in plasma only what is strictly necessary for the survival of its organs.
Hemoglobin, could the liver itself betray it? Precisely, explains Carlos Taboada. Because millions of nanocrystals surround the organ, forming a kind of mirror that returns light. The red blood cells are almost entirely hidden in the eyes of the predators. Hide this blood that I cannot see!
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