Tropical glass frogs have discovered a completely new type of camouflage called boundary diffusion. These amphibians translucent, which allows them to automatically adjust their brightness to the background. More transparent paws blur the edges of the body of frogs and allow them to further blend in with the substrate. Description of an unusual adaptation is given in the article in the journal Proceedings of the National Academy of Sciences.
Transparency seems to be the perfect camouflage, because it provides invisibility on any background. It is not surprising that in an attempt to protect themselves from predators, many aquatic animals have become transparent. However, on land such adaptation is much worse due to the difference of refractive indices of air and biological tissues. In addition, a transparent land animals would have been defenseless against the UV study, which is usually reflected by the pigments.
One of the few land animals with partially transparent bodies of glass frogs (Centrolenidae), inhabiting Central and South America. Through the skin and muscle on their chest and stomach are clearly visible internal organs and bones. However, the upper side of the body of these amphibians rather translucent and painted in different shades of green.
Among zoologists, there is no consensus whether the translucent glass frogs coloration works as camouflage. To understand the functions decided by a team of researchers headed by James Barnett (James B. Barnett) from McMaster University.
In the first step the researchers took a picture of the two types of glass frogs on leaves and on white paper. In total, the lens were 25 individuals Teratohyla midas and 30 individuals Espadarana prosoblepon. The obtained pictures were evaluated using computer models that simulate the di-, tri – and tetrachromatic sight of different predators. It turned out that in all cases the brightness of the frog adapts to the background, allowing them to better blend in with it. The effect is not due to the active change of color, and the translucency of the body. Thus the apparent brightness of the more transparent paws varies stronger than that of the body.
Then the members of the team generated several images of frogs, taking as sample T. midas. Some of them, like these glass frogs legs were more transparent than the back, while others – Vice versa. In addition, the selection was fully transparent and fully opaque image. Computer of amphibians placed in the pictures of leaves and then asked for twenty volunteers to find them. To detect frogs with translucent color elements, the participants spent more time.