Deep Breaths: The Evolution Of Diving Mammals

April Flowers for redOrbit.com – Your Universe Online

A new study led by the University of Liverpool sheds new light on how diving mammals, such as the sperm whale, have evolved to be able to submerge for long periods underwater without breathing.

The international team, led by Dr. Michael Berenbrink, from the University’s Institute of Integrative Biology, identified a distinctive molecular signature of the oxygen-binding protein myoglobin in the sperm whale and other diving mammals. This discovery allowed the team to trace the evolution of the muscle oxygen stores in more than 100 mammalian species and their fossilized ancestors.

At high concentrations, proteins tend to stick together. This impairs the function of the proteins, making it unclear how myoglobin was able to help the body store enough oxygen to allow mammals, such as whales and seals, to endure underwater for long periods of time without breathing. Elite mammalian divers can hold their breath for over an hour while they hunt in the depths of the oceans. For example, sperm whale dives can last as long as 90 minutes, while dolphins and other whales can endure for up to 20 minutes. Land mammals, on the other hand, such as humans, can generally only hold their breath for a few minutes.

The Telegraph reports that the record dive for humans is 19 minutes – set by Swiss freediver Peter Colat.

Berenbrink explains, “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.”

This increased charge causes the proteins to repel each other. This prevents them from forming clumps that can impede their ability to carry oxygen. The team suggests this allows the diving animals to pack more myoglobin into their muscles without harming their efficiency.

Dr. Scott Mirceta, a PhD student on the project, added, “Our study suggests that the increased electrical charge of myoglobin in mammals that have high concentrations of this protein causes electro-repulsion, like similar poles of two magnets. This should prevent the proteins from sticking together and allow much higher concentrations of the oxygen-storing myoglobin in the muscles of these divers.”

The team wasn’t satisfied with just examining modern day animals.

“By mapping this molecular signature onto the family tree of mammals, we were able to reconstruct the muscle oxygen stores in extinct ancestors of today’s diving mammals. We 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 waters some 65 million years ago,” said Berenbrink.

“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. This is important for understanding the prey items that were available to these extinct animals and their overall importance for past aquatic ecosystems,” added Mirceta.

Beyond understanding deep diving mammals, the research findings could also help improve understanding of a number of human diseases where protein aggregation is a problem, such as Alzheimer’s disease and diabetes, and could inform the development of artificial blood substitutes.

The results of the study were published in the journal Science.

Dr. Berenbrink notes, “This finding illustrates the strength of combining molecular, physiological and evolutionary approaches to biological problems and, for the first time, allows us to put ‘flesh’ onto the bones of these long extinct divers.”

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