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Better oxygen storage deepens the dive

A male hooded seal on the pack ice off eastern Canada. Hooded seals have the highest ever recorded concentrations of the oxygen-storing protein myoglobin in their muscles and are known to dive for up to 52 minutes.
[Image courtesy of J. Burns]

All mammals—including you—have oxygen-storing molecules, but deep-diving mammals like whales have adapted special versions of these molecules that let them hold their breaths for long periods, and a new study provides insight into just when this special capability evolved.

Because deep-diving mammals can hold their breaths for long periods (in some cases, for over an hour), they have an advantage when it comes to feeding; they can dive deep and feed where other animals cannot.

They are able to hold their breaths so long and dive so deep because their muscles can store extra oxygen, which the body needs for energy.

In mammals, a protein called myoglobin is responsible for storing oxygen. Diving mammals have been shown to have a higher concentration of myoglobin in their muscles than mammals like you and I, but scientists have not understood when in evolutionary history this came to be.

Now, Scott Mirceta from the Institute of Integrative Biology at the United Kingdom's University of Liverpool has shed light on the matter. Mirceta and his team traced the evolutionary history of myoglobin in deep-diving mammals over a roughly 200 million year history.

To get started, the team evaluated the muscle concentration of myoglobin in mammalian divers alive now, finding that it was linked with a special molecular trait—an increased charge on the surface of the myoglobin molecule. Next, they used a process called ancestral sequence reconstruction to determine myoglobin concentration in deep-diving mammals' ancient relatives. They did in this 130 mammalian species.

The researchers found that all ancestors of mammalian divers have myoglobin with the special, elevated charge. The charge is important: it causes myoglobin molecules to repel one another, and thus—along with the oxygen they bind—to remain separated and more readily available for muscle use.

The discovery of a special type of myoglobin in deep-diving mammals provides insight into how mammals came to dive deep. Furthermore, the historical approach Mirceta and colleagues took better explains when in evolutionary history specialized myoglobin arrived on the scene to help land-based mammals transition to life in the water.