Adaptive respiratory variation in 4 chromosomal species of mole rats.

Oxygen and carbon dioxide pressures were measured in subcutaneous gas pockets of 4 chromosomal species of the Spalax ehrenbergi complex. Oxygen pressures of 11.8, 13.6, 16.9, and 17.2 torr and CO2 pressures of 84.2, 82.9, 80.1, and 64.1 torr were measured for the chromosomal species 2n = 52, 54, 58, and 60, respectively. The differences between the 4 chromosomal species in their subcutaneous gas tension appear to reflect adaptive respiratory variation associated with geographic variation in climate. It underlies an important respiratory physiological correlate of ecological speciation in the extremely hypoxic and hypercapnic subterranean environment.