Seismic Communication Signals in the Blind Mole Rat are Processed by the Auditory System

Abstract

The blind mole rat (Spalax ehrenbergi) is a solitary, highly aggressive and essentially blind, subterranean rodent that spends its entire life in underground tunnels. Each mole rat excavates its own tunnel system and accidental encounters between two individuals are usually fatal for at least one of them. However, there is a need for females and males to meet during the mating season. To avoid undesired encounters between conspeci- fics and yet enable contact between males and females for reproductive purposes, a signal- ing system is necessary to allow communication between individuals inhabiting neighboring tunnels. The question thus arise as to how do mole rats located in different tunnel systems communicate in their underground environment? We and others (Rado et al., 1987; Heth et al., 1987) have previously demonstrated that the blind mole rat produces patterned substrate-borne (seismic) vibrations by tapping its head on the roof of the tunnel. Such tapping behavior has been observed both in nature and under laboratory conditions (Rado et al., 1987). Typically, vibrations produced by a mole rat placed in an experimental Plexiglas tube elicited tapping behavior by another specimen placed in the same tube (yet separated by some barrier) or in a second tube that was in physical contact with the first one (Rado et al., 1987). In such “dialogues”, while one mole rat was producing the vibrations the other usually pressed its cheek and lower jaw against the vibrating wall of the tube, and appeared to be “listening”. When the two compartments were separated so that no vibrations could cross between them, the dialogue essentially ceased. Based on these behavioral observations and on some unique morphological properties of the mole rat’s middle ear and the lower jaw (Rado et al., 1987; Rado et al., 1989; Bruns et al., 1988; Burda et al., 1989) we suggested that blind mole rats use these seismic vibrations for intraspecific communication and that these vibrations are mediated to the auditory system by bone conduction. This notion has been challenged recently by Nevo et al. (1992) who suggested that the seismic signals are perceived and processed by the somato- sensory system. In this study we present electrophysiological evidence corroborating our assumption that the seismic signals used by the blind mole rat for long distance communication are indeed perceived and processed primarily by the auditory system.