A team of international scientists report in the June 2013 edition of the journal Science how sperm whales and other diving mammals evolved to survive for long periods underwater without breathing.
Biologists Kevin Campbell and Anthony Signore at the University of Manitoba worked with a team of researchers to identify a distinctive molecular signature in the oxygen-binding protein myoglobin in all lineages of diving mammals―from tiny water shrews to blue whales. The finding, moreover, allowed them to trace the evolution of dive capacity in the diving mammals’ fossil ancestors.
Elite mammalian divers can hold their breath for well over an hour when they hunt in the depths of the oceans, while land mammals, such as humans, can breath-hold for only a few minutes. Much of this ability is attributed to myoglobin, which is present in high concentrations in the muscles of elite mammalian divers. Until now, however, very little was known about how this molecule is adapted in champion divers.
“The trick, it appears, is to evolve a protein with a strong positive surface charge” explains Campbell. “The resulting molecular repulsion allows the oxygen-storing myoglobin of divers to accrue in much higher concentrations.”
“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” says team leader Michael Berenbrink of the University of Liverpool, UK.
Scott Mirceta, who worked in both labs, added: “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.”
“In addition to predicting the physiological properties of fossil divers, using ancient DNA technology we are able to strengthen our dataset by actually incorporating recently extinct species, such as the woolly mammoth and the gigantic Steller’s sea cow (an Arctic relative of the manatee)” says Anthony Signore, a Ph.D. student in the Campbell lab who sequenced the myoglobin gene from these and other related species.
Discussing the results, Campbell notes, “What’s more remarkable is that telltale signs of this novel attribute remain in the DNA of terrestrial mammals with an aquatic ancestry, such as spiny echidnas, subterranean moles, and even elephants (and mammoths), for which an amphibious past has long been suggested.”
“This finding not only illustrates the strength of evolutionary theory, but, for the first time, allows us to put ‘flesh onto the bones’ of these long extinct divers,” concludes Berenbrink.
The research could help improve understanding of a number of human diseases where protein aggregation is a problem, such as Alzheimer’s and diabetes, and may also have potential applications in industrial protein production.