How Elite Diving Mammals Evolved Their Underwater Endurance

A novel study of electrical signals of proteins has allowed researchers to effectively map the evolution of sea mammals' ability go long periods of time without oxygen. Elite diving mammals, such as the sperm whale, are capable of surviving underwater without air for more than an hour because of myoglobin, the same oxygen-storing protein that gives meat its red color.

Concentrations of myoglobin in some elite diving mammals' muscles are so high that the flesh is almost black in color.

But until now, little was understood about how myoglobin adapted in deep sea endurance divers.

Researchers from University of Liverpool identified a distinctive molecular signature in myoglobin, which allowed them to trace the evolution of the muscle oxygen stores in more than 100 mammalian species, including their fossil ancestors.

The team identified the positive electrical charge on the surface of the myoglobin that increases in mammals that can dive over long periods of time. Researchers believe that the positive charge is what enables the animals to dive longer, as normally myoglobin at such high concentrations causes the proteins to clump together and become useless.

"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. 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," said Michael Berenbrink, an integrative biologist at University of Liverpool.

By mapping the molecular signature onto the family trees of mammals and using known information about animals' body mass, the researchers were able to map the myoglobin contents in extinct ancestors of today's diving mammals. It appears that today's deep-diving whales can last longer underwater than their ancestors. An early whale ancestor called Pakicetus couldn't stay underwater longer than a minute and a half, while a creature called Basilosaurus, which lived about 15 million years after the Pakicetus, was able to be submerged for 17 minutes, according to a report by Nature.

"If you give me a myoglobin sequence, I can tell you if the animal is a good diver or not," Berenbrink told Nature.

The results of Berenbrink's study suggested that the increased electrical charge of myoglobin in mammals that have high concentration of the protein causes an electro-repulsion similar to two magnets. The effect results in the proteins in the animals not sticking together and allows higher concentration of oxygen in the divers

"We are really 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," Scott Mirceta, a PhD student who also worked on the project, said in a statement. "This is important for understanding the prey items that were available to these extinct animals and their overall importance for past aquatic ecosystems."

The research, done in collaboration with the University of Manitoba, Canada, and the University of Alaska, US, is published in the journal Science.