Sleeping Glass Frogs Store Blood In Their Liver To Become Transparent
Small glass frogs store blood in liver. They take almost 90 percent of their red blood cells out of circulation when they go to sleep for the day. A new study finds that the colorful cells are hidden by a mirror-like surface on the inside of the frog liver, where they are stuffed into small pockets.
Small glass frogs store blood in liver. They take almost 90 percent of their red blood cells out of circulation when they go to sleep for the day. A new study finds that the colorful cells are hidden by a mirror-like surface on the inside of the frog liver, where they are stuffed into small pockets. Biologists have known for a long time that glass frogs have clear skin, but hiding bright red blood is a new way for vertebrates to hide.
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Transparency is rare in general for vertebrates. If it wasn’t for that green skin on their back, you would probably be able to read a newspaper through them.- Jesse Delia, American Museum of Natural History in New York
Transparency serves as a sort of camouflage that aids in maintaining crypsis in immobile animals. Transparency is a trait shared by many species, although it is especially difficult to achieve in vertebrates due to the attenuation of light by red blood cells.
Since most of a glass frog's red blood cells are "hidden" in the liver, the frog can retain its high degree of transparency. The frogs are able to achieve transparency at a time when they are most defenseless thanks to this tactic. To better comprehend hemodynamics, it may help to learn how the liver is packed.
Transparency is a sophisticated sort of camouflage used by animals, requiring a wide variety of systems that work together to minimize the scattering and absorption of light at all points throughout the body. Transparency is difficult to achieve in vertebrates because their blood is full of red blood cells (RBCs), which heavily absorb light.
Photoacoustic imaging of RBCs in vivo reveals that when glassfrogs are at rest, they remove 89% of their RBCs from circulation and pack them inside their liver, increasing transparency by a factor of two to three.
Therefore, vertebrates need both transparent tissues and active processes that "clean" respiratory pigments from these tissues in order to be completely see-through. Glassfrogs provide light on metabolic, hemodynamic, and blood-clot studies due to their capacity to control the position, density, and packing of RBCs without clotting.
By concentrating their blood supply in the liver when they rest, glass frogs may increase their see-throughness by as much as 61%. Scientists are interested in the frogs' ability to pool blood in this manner without developing deadly clots because they believe it may provide light on how to avoid such clots in other animals and people.
The amphibians, which are about the size of a marshmallow, spend their days resting on brilliant green leaves and their nights searching for food. To avoid being detected by predators, glass frogs have evolved a unique ability to partially conceal their bodies from view. However, this is a difficult biological challenge, since most animals must constantly pump red blood cells throughout the body to give oxygen to their tissues.
When Delia and his team saw that sleeping frogs were considerably more see-through than waking ones, they started to look into the frogs' transparency more thoroughly. The frogs' opacity was evaluated by shining light of several wavelengths through them during both active and resting states. When the frogs are sleeping, they become up to 61% more see-through, the researchers observed.
Researchers found that glass frogs "hide" around 89% of their red blood cells in their liver when they sleep by utilizing photoacoustic imaging to track the flow of blood in living animals in real-time. Frogs' livers grew by around 40% on average to make room for this. The frogs grew more translucent and their livers shrank once they awakened and their blood flow picked up.
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The heart stopped pumping red, which is the normal color of blood, and only pumped a bluish liquid.- Carlos Taboada, Duke University
Glassfrogs turn transparent by storing blood in their liver
A glass frog's translucency may be increased by a factor of two or three if its red blood cells are hidden from view. Snack-sized frogs spend the day hidden like small shadows on the undersides of the leaves high in the forest canopy, so greenish transparency might mean a lot to them.
When red blood cells are packed together in the bodies of most vertebrates, clotting occurs. However, the amphibians don't seem to suffer any ill effects from this practice. Delia said that they don't know how glass frogs avoid coagulation, but they hope that their findings will help researchers find better ways to treat blood clots in people.
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