Auditory-vocal coupling in the naked mole-rat, a mammal with poor auditory thresholds
Naked mole-rats are extremely social and extremely vocal rodents, displaying a wide range of functionally distinct call types and vocalizing almost continuously. Their vocalizations are low frequency, and a behavioral audiogram has shown that naked mole-rats, like other subterranean mammals, hear only low frequencies. Hence, the frequency range of their hearing and vocalizations appears to be well matched. However, even at low frequencies, naked mole-rats show very poor auditory thresholds, suggesting vocal communication may be effective only over short distances. However, in a tunnel environment where low frequency sounds propagate well and background noise is low, it may be that vocalizations travel considerable distances at suprathreshold intensities. Here, we confirmed hearing sensitivity using the auditory brainstem response; we characterized signature and alarm calls in intensity and frequency domains and we measured the effects of propagation through tubes with the diameter of naked mole-rat tunnels. Signature calls—used for intimate communication—could travel 3–8 m at suprathreshold intensities, and alarm calls (lower frequency and higher intensity), could travel up to 15 m. Despite this species’ poor hearing sensitivity, the naked mole-rat displays a functional, coupled auditory-vocal communication system—a hallmark principle of acoustic communication systems across taxa.