Biologists solve mystery of crocodile’s ability not to breathe 00:34

Scientists have studied the properties of crocodile hemoglobin, which allows it to sit underwater for a long time. article about it published In Current Biology.

Crocodiles are famous for their ability to hunt from ambush. While underwater, they wait for the victim, then suddenly jump up, glide above the surface and grab the animal with their teeth. However, crocodiles breathe air and can only dive by holding their breath. Because of the presence of a special type of hemoglobin in the blood, the reptile can sit without breathing for several hours.

Jay Stortz of the University of Nebraska at Lincoln and his colleagues set out to find out how exactly crocodiles evolved this unique trait among all jawed vertebrates. Hemoglobin binds to oxygen in the lungs and then releases it in the tissues. In most vertebrates, the ability of hemoglobin to capture and retain oxygen is determined by organic phosphates, which when bound to hemoglobin cause it to release gas. However, in crocodiles, bicarbonate formed during the breakdown of carbon dioxide is used instead of phosphate. Because tissues produce so much carbon dioxide, they also indirectly produce too much bicarbonate, which “induces” hemoglobin to distribute oxygen to the tissues that need it most.

To find out how such a system might have emerged during evolution, the authors decided to examine three types of reconstructed hemoglobin: a distant ancestor of 240-million-year-old crocodiles (archosaurus), the last common ancestor of all birds, and an 80-million-year-old common ancestor of modern crocodiles. It turned out that only the hemoglobin of the direct ancestor of crocodiles does not bind phosphates and is sensitive to bicarbonate.

Later, scientists began adding crocodile-specific mutations to archosaurus hemoglobin. As a result, the authors determined which mutations made archosaurus hemoglobin more similar to modern crocodile hemoglobin.

It turned out that the evolutionary changes in the reaction of hemoglobin to bicarbonates and phosphates resulted from different sets of mutations, and that the enhancement of one mechanism was not due to the loss of the other. That is, bicarbonate sensitivity was turned on and phosphate sensitivity was turned off separately.

The scientists conclude that a combination of mutations can lead to functional changes greater than the sum of their individual effects. A mutation that does not produce a functional effect on its own can pave the way for other mutations with clear and immediate consequences in many ways.