Biologists have solved the mystery of the crocodile’s ability not to breathe

(ORDO NEWS) — Scientists have studied the features of crocodile hemoglobin, which allow him to sit under water for a long time.

Crocodiles are famous for their ability to hunt from ambush. They wait for the victim, being under water, after which they abruptly jump up, soar above the surface and grab the animal with their teeth.

However, crocodiles breathe air, and can only dive by holding their breath. Due to the presence of a special type of hemoglobin in the blood, a 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 exactly how crocodiles developed this feature, the only one of 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 attached to hemoglobin, cause it to release gas.

But in crocodiles, instead of phosphates, bicarbonate is used, which is formed during the breakdown of carbon dioxide.

Since tissues produce a lot of carbon dioxide, they also indirectly generate a lot of bicarbonate, which in turn “induces” hemoglobin to distribute oxygen to the tissues that need it most.

To find out how such a system could have arisen in the course of evolution, the authors decided to study reconstructed hemoglobin of three types: a distant ancestor of crocodiles (archosaurus) aged 240 million years, the last common ancestor of all birds, and a common ancestor of modern crocodiles 80 million years old.

It turned out that only the hemoglobin of the direct ancestor of crocodiles did not bind phosphates and was sensitive to bicarbonate.

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

It turned out that evolutionary changes in the reaction of hemoglobin to bicarbonates and phosphates were caused by different sets of mutations, and the strengthening of one mechanism did not depend on the loss of the other.

In other words, bicarbonate sensitivity was switched on and phosphate sensitivity was switched off separately.

The scientists conclude that a combination of mutations can lead to functional changes that are greater than the sum of their individual effects.

A mutation that produces no functional effect on its own can open the way for other mutations in many ways, with obvious and immediate consequences.

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