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ShareWashington: A new study has explained how marine mammals like seals and whales evolved to dive in the sea and cope with the needs of life in the aquatic environment.
An aquatic lifestyle imposes serious demands on the organism, and this is true even for the tiniest molecules that form our body.
When the ancestors of present marine mammals initiated their return to the oceans, their physiology had to adapt radically to the new medium.
Michael Berenbrink and his colleagues at Liverpool University, England, have been studying how myoglobin, the molecule responsible for delivering oxygen to the muscles during locomotion, has been modified in seals and whales to help them cope with the needs of life at sea.
The researchers found evidence indicating that the net positive charge of this protein is increased in marine mammals compared with terrestrial relatives, and they have speculated that this may help in improving the solubility of the molecule.
This is important as divers may contain 10 times more myoglobin in their muscles than terrestrial animals.
The team also found a conspicuous increase of the amino acid histidine in the myoglobin of strong divers, which may allow the animal to deal better with the accumulation of lactic acid that is frequent during long dives.
To confirm that this was indeed the result of evolutionary pressure, the researchers went on to study the molecular sequence of myoglobin in small aquatic mammals such as beavers, muskrats, and water shrews, which only dive for short periods of time, to see if they could also find evidence of the same trend.
Indeed, the net charge of the myoglobin molecule in aquatic rodents was twice as high as in their strictly terrestrial relatives, and the trend was also verified for some semi-aquatic species of insectivores.
"This work will contribute to our understanding of protein solubility in general,"Berenbrink said. "It will also allow the analysis of natural selection on protein structure/function in multiple parallel cases in which a high muscle myogobin content evolved, such as in divers, but also in burrowing animals that normally experience hypoxia."
