Scientists Solve Mystery Behind Diving Marine Mammals: How Whales Hold Their Breath

First Posted: Jun 14, 2013 07:41 AM EDT

Sure, we can swim and dive underwater, but we don't have the amazing evolutionary adaptation that marine mammals possess. While we can only hold our breath for mere minutes while actively swimming, diving mammals, such as the sperm whale, can survive far longer underwater. Now, scientists have solved the mystery behind this amazing adaptation in marine mammals.

While sharing many mammalian characteristics with whales, sea lions and other marine mammals, humans lack the innate ability to hold their breath for long periods of time. In fact, the longest a person has ever held his breath is a mere 22 minutes and 22 seconds--and that's after breathing pure oxygen first and essentially "sitting" underwater rather than actively moving. In contrast, sperm whales can actively swim beneath the waves for up to two hours, though most dives last an average of 45 minutes.

In order to find out how marine species manage to accomplish this feat, researchers examined the sperm whale. They were able to find a distinctive molecular signature of the oxygen-binding protein myogloblin, which is what gives meat its red color. This protein is present in high concentrations in elite mammalian divers. In fact, it's so high that the muscles of the animal appear almost black in color. Until now, though, the scientists weren't sure how the molecule is adapted in diving mammals.

"We studied the electrical charge on the surface of myoglobin and found that it increased in mammals that can dive underwater for long periods of time," said Michael Berenbrink, who led the team, in a news release. "We were surprised when we saw the same molecular signature in whales and seals, but also in semi-aquatic beavers, muskrats and even water shrews."

After discovering this molecular signature, the scientists then mapped it onto the family tree of mammals. This allowed them to reconstruct the muscle oxygen stores in extinct ancestors of today's diving mammals. In fact, they were even able to report the first evidence of a common amphibious ancestor of modern sea cows, hyraxes and elephants that lived in shallow African water about 65 million years ago.

So how does this myogoblin work? It turns out that the increased electrical charge of this molecule in mammals that have high concentrations of this protein causes electro-repulsion--similar to poles of two magnets. This prevents the proteins from sticking together and allows for much higher concentration of myoglobin. This, in turn, allows the mammals to store more oxygen.

"We really are excited by this new find, because it allows us to align the anatomical changes that occurred during the land-to-water transitions of mammals with their actual physiological diving capacity," said Scott Mirceta, one of the researchers, in a news release. "This is important for understanding the prey items that were available to these extinct animals and their overall importance for past aquatic ecosystems."

The findings are published in the journal Science.

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