HEARING AND SOUND LOCALIZATION IN BLIND MOLE RATS (SPALAX-EHRENBERGI)

Two blind mole rats were tested for their ability to detect and localize sound. The results indicate that blind mole rats have severely limited, and probably degenerate, auditory abilities. Although their 60-dB low-frequency hearing limit of 54 Hz is within the range for other rodents, the highest frequency they can hear at a level of 60 dB SPL is only 5.9 kHz, giving them the poorest high-frequency sensitivity yet observed in any mammal. In addition they have poor sensitivity as indicated by the fact that their lowest threshold is only 32 dB SPL (at 1 kHz). Finally, they are unable to localize brief sounds but retain a rudimentary ability to localize sounds of 0.5 s or longer. These results, combined with those of previous studies of subterranean species (i.e., blind mole rats, naked mole rats, and pocket gophers), suggest that poor auditory sensitivity, the loss of high-frequency hearing, and an inability to localize brief sounds is a degenerate state which may be characteristic of subterranean mammals. Thus it appears that an exclusive adaptation to a subterranean lifestyle (where airborne sound propagates poorly and where directional responses are limited by the tunnels) can result in vestigial auditory abilities just as the absence of light results in vestigial vision.