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First published online February 4, 2005
Journal of Experimental Biology 208, 647-659 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01396
Evidence for the use of reflected self-generated seismic waves for spatial orientation in a blind subterranean mammal
1 Department of Zoology, Faculty of Life Sciences, Tel-Aviv University, Tel
Aviv 69978, Israel
2 Department of Geophysics and Planetary Sciences, Faculty of Exact
Sciences, Tel-Aviv University, Tel Aviv 69978, Israel
* Author for correspondence at present address: Harvard University, Department of Molecular and Cellular Biology, 16 Divinity Avenue, Cambridge, 02138 MA, USA (e-mail: kimhi{at}fas.harvard.edu).
Accepted 15 November 2004
Subterranean mammals like the blind mole-rat (Rodentia: Spalax ehrenbergi) are functionally blind and possess poor auditory sensitivity, limited to low-frequency sounds. Nevertheless, the mole-rat demonstrates extremely efficient ability to orient spatially. A previous field study has revealed that the mole-rat can assess the location, size and density of an underground obstacle, and accordingly excavates the most efficient bypass tunnel to detour around the obstacles. In the present study we used a multidisciplinary approach to examine the possibility that the mole-rat estimates the location and physical properties of underground obstacles using reflected self-generated seismic waves (seismic `echolocation').
Our field observations revealed that all the monitored mole-rats produced low-frequency seismic waves (250-300 Hz) at intervals of 8±5 s (range: 1-13 s) between head drums while digging a bypass to detour an obstacle. Using a computerized simulation model we demonstrated that it is possible for the mole-rat to determine its distance from an obstacle boundary (open ditch or stone) by evaluating the amplitude (intensity) of the seismic wave reflected back to it from the obstacle interface. By evaluating the polarity of the reflected wave the mole-rat could distinguish between air space and solid obstacles. Further, the model showed that the diffracted waves from the obstacle's corners could give the mole-rat precise information on the obstacle size and its relative spatial position.
In a behavioural experiment using a special T-maze setup, we tested whether the mole-rat can perceive seismic waves through the somatosensory system and localize the source. The results revealed that the mole-rat is able to detect low frequency seismic waves using only its paws, and in most cases the mole-rats determined accurately the direction of the vibratory source. In a histological examination of the glabrous skin of the mole-rat's paws we identified lamellate corpuscle mechanoreceptors that might be used to detect low frequency seismic waves.
The combined findings from these different approaches lead us to suggest that a specialized seismic `echolocation' system could be used by subterranean mammals to determine the most energy-conserving strategy with which to bypass an obstacle, as well as to estimate their distance from the surface, keeping their tunnels at the optimal depth.
Key words: spatial orientation, obstacle, echolocation, seismic signal, Spalax ehrenbergi, mole-rat, subterranean mammal
This article has been cited by other articles:
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  R. Avni, Y. Tzvaigrach, and D. Eilam Exploration and navigation in the blind mole rat (Spalax ehrenbergi): global calibration as a primer of spatial representation J. Exp. Biol., September 1, 2008; 211(17): 2817 - 2826. [Abstract] [Full Text] [PDF]
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Y. van Bergen GOOD VIBRATIONS J. Exp. Biol., February 15, 2005; 208(4): i - i. [Full Text] [PDF]
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