Special properties of an oxygen-binding protein in the muscles of marine mammals, such as seals, whales and dolphins, are the reason these animals can hold their breath underwater for long periods of time, according to a new study.
Many of these mammalian divers can hold their breath underwater for over an hour, while land-based mammals, such as humans, can only do so for a few minutes at most.
Scientists from the University of Liverpool, who led the study, were able to identify a unique molecular characteristic of myoglobin, an iron and oxygen-binding protein found in sperm whales and other diving mammals. Until this finding, very little was known about how the molecule is adapted in the diving marine mammals.
The researchers, in collaboration with the University of Manitoba and University of Alaska, found a high concentration of myoglobin, the substance that makes meat look red, in the muscles of the mammalian divers. In fact, the amount was so high in the muscle that it almost looked black in color.
This discovery allowed the scientists to trace the evolution of how the muscles of more than 100 species of mammals, including fossil remains of their ancient predecessors, were able to store oxygen.
“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 Dr. Michael Berenbrink, from the University of Liverpool, who led the international team of scientists. “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.”
Mapping the unique molecular signature of myoglobin throughout the mammalian family tree allowed scientists to recreate the muscle oxygen stores found in the extinct ancestors of today’s diving mammals. The team then was able to find the first evidence of a common amphibious forefather of modern sea cows, hyraxes and elephants that lived 65 million years ago in shallow African waters.
“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,” said Dr. Scott Mirceta, a member of the research team. “This should prevent the proteins from sticking together and allow much higher concentrations of the oxygen-storing myoglobin in the muscles of these divers.”
“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,” said Berenbrink.
Watch a video on this discovery (University of Liverpool/BBSRC)