June 17th, 2013 by James Ayre
Marine mammals possess truly remarkable underwater endurance — some of them, such as the sperm whale, can remain submerged during their dives for as long as an hour and a half. That’s an hour and a half of physical exertion on a single breath. What physiological adaptions allow such impressive abilities? The answers to that question are now becoming more clear thanks to new research from the University of Liverpool.
The new research identified “a distinctive molecular signature of the oxygen-binding protein myoglobin in the sperm whale and other diving mammals, which allowed them to trace the evolution of the muscle oxygen stores in more than 100 mammalian species, including their fossil ancestors.”
To provide context, myoglobin is the the primary oxygen-carrying pigment of muscle tissues, it’s what gives the meat of diving mammals such a dark, almost black, color. It’s present in the muscles of said diving mammals in very high concentrations — especially in those most known for deep-diving. Until this new research though it wasn’t very clear if/how the molecule itself was adapted in deep-diving mammals.
The University of Liverpool explains:
Proteins tend to stick together at high concentrations, impairing their function, so it was 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, while land mammals, such as humans, can hold their breath for only a few minutes.
Dr Michael Berenbrink, of the University’s Institute of Integrative Biology, states: “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.
“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.”
Dr Scott Mirceta, PhD student, states: “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.”
“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.”
The research was funded by the Biotechnology and Biological Sciences Research Council — with the hope that the research would provide insight into a number of different human diseases/disorders. Primarily those where protein aggregation is a problem — Alzheimer’s, diabetes, etc. There is also the possibility that the research may help in the development of artificial blood substitutes.
Dr Berenbrink says: “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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