Researchers writing in the journal BMC Evolutionary Biology have made the first identification of a new type of adaptation in the blood of moles which allows more efficient transport of carbon dioxide. This “super hemoglobin” facilitates the moles’ burrowing behaviour and helps them survive long periods of time in dark, stifling conditions.

Kevin Campbell from the University of Manitoba, Canada, worked with a team of researchers to study the blood of three underground species of North American moles. He says: “Unlike terrestrial animals, moles are routinely exposed to conditions of low oxygen and high carbon dioxide. Burrowing is difficult in itself, but is made even more challenging by the requirement to re-breathe their own expired air.”

The primary function of blood is to carry oxygen from the lungs to the working muscles and carbon dioxide in the opposite direction.

Campbell adds: “We’ve found that one species, the Eastern mole, appears to be uniquely adapted to underground life through the evolution of a special kind of hemoglobin in its blood that greatly enhances its carbon dioxide carrying capacity.”

The researchers determined the genetic code of the different hemoglobin components in three mole species and measured how well these components bind to their usual target molecules. They also tested the oxygen binding properties of whole blood samples.

Discussing the results, Campbell explains, “It has been speculated that the main mechanism for the moles adaptation to subterranean life revolves around the molecule 2,3-diphosphoglycerate, or DPG. It modulates hemoglobin’s oxygen binding inside the blood cells. However, in the hemoglobin of the eastern mole, the key sites which would normally bind DPG are deleted, thereby allowing for the binding of additional carbon dioxide molecules.”
 
Roy Weber of the University of Aarhus, Denmark, and co-author of the study, notes: “Low oxygen concentrations and high levels of carbon dioxide in blood are life-threatening symptoms in patients with chronic obstructive lung diseases such as emphysema and bronchitis. Our research provides invaluable information for the development of new hemoglobins by gene therapy.”