Glass frogs, native to the rainforests of Central and South America, are masters of stealth, turning almost invisible while sleeping to evade predators.
American researchers recently reported in the American journal 'Science' that the glass frog's magical ability may be because red blood cells in the blood are concentrated in the liver, making the whole body transparent.
About the size of a paper clip, glass frogs are nocturnal. When they sleep under the leaves during the day, they turn their green skin into transparent flakes and form themselves like dewdrops in sunlight to avoid predation by predators such as spiders and snakes. When they wake up at night to feed or mate, their bodies turn back an opaque reddish-brown color.
The researchers brought several glass frogs into the lab and observed them, suggesting whether or not the glass frogs' bodies became transparent as their bodies were 34 to 61 percent more transparent when they were asleep than when they were active. red blood cells in blood vessels.
One of the study's authors, Duke University biologist Carlos Taboada, said that when the animals slept, their veins seemed to have no blood, and when they awoke, blood began to flow and the transparency decreased. of the body.
Taboada and his colleagues therefore used photoacoustic imaging to map the ultrasound waves emitted by light-absorbing glass frog red blood cells. As a result, it was found that when glass frogs sleep during the day, their livers fill up with red blood cells and swell by about 40%. While the livers of other tree frogs normally only hold 12% of red blood cells, the livers of glass frogs can retain up to 89% of all red blood cells.
That means the glass frog's blood is deprived of oxygen for about 12 hours a day, said biologist Jesse Delia of the American Museum of Natural History. How glass frogs do this is unclear to researchers. For most animals, death means death if the blood is not oxygenated for several hours.
Juan Manuel Guayasamin, a biologist at the University of San Francisco in Quito, Ecuador, said the study "completely reveals" how glass frogs "hide" blood in their livers, making their bodies transparent.
Researchers were also amazed at the glass frog's ability to concentrate large numbers of red blood cells in one part of its body without clotting. Some scientists not involved in the study believe that solving this riddle could lead to better treatment of diseases related to blood clotting in humans.
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