Eastern moles evolve different haemoglobin to facilitate fast tunnelling

Most moles spend the vast majority of their lives underground and consequently have evolved numerous adaptations to facilitate this. Over time this has included the development of large, broad front paws with strong claws for digging, and the gradual loss of their eyesight as it is not selected for in the dark conditions. Different species of mole have also been shown to have further diversified in their adaptations to their environment, as in the case of the Star-nosed mole which has developed an intricately shaped nose in order to feed on small prey items in the wet lowland areas in which it lives.

Eastern moles in particular prefer moist, invertebrate-rich soil in which they can construct their extensive burrow networks. As a result they are constantly exposed to hypoxic and hypercapnic environments due to the reduced gas exchange of the damp soils with the surface air. Moles are fast burrowers and this incurs high metabolic costs in terms of respiration, which are exacerbated by the re-breathing of expired air when tunnelling.

Recent research published in BMC Evolutionary Biology shows that in order to cope with this, the Eastern mole has undergone adaptive modifications in its haemoglobin function.

Research article
Molecular basis of a novel adaptation to hypoxic-hypercapnia in a strictly fossorial mole
Kevin L Campbell, Jay F Storz, Anthony V Signore, Hideaki Moriyama, Kenneth C Catania, Alexander P Payson, Joseph Bonaventura, Joerg Stetefeld, Roy E Weber
BMC Evolutionary Biology 2010, 10:214 (16 July 2010)
[Abstract] [Full Text] [PDF] [PubMed] [Related articles]

Mammalian haemoglobin generally falls into two discrete categories; haemoglobin with very high oxygen affinity that has a high reactivity to concentrations of allosteric effectors such as 2,3-diphosphoglycerate (DPG) in the red blood cell and so is stabilised by these, and haemoglobin with low oxygen affinity which has much lower concentrations of DPG in the red blood cells and reacts weakly to these. DPG modulates haemoglobin’s oxygen binding inside the red blood cell and in this article by Dr Kevin Campbell et al, it is shown that the haemoglobin of the Eastern mole has evolved to a position where the key sites which usually bind to DPG are deleted, and so this allows for additional binding from carbon dioxide molecules. This research suggests that this unique haemoglobin enhances carbon dioxide carrying capacity in the Eastern mole’s red blood cells and is specifically designed to facilitate burst tunnelling activities in gas-exchange impeded burrows.

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