Dr. Matthew Mason: Further Information...
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Mason, M.J. & Narins, P.M. (2002) Seismic sensitivity in the desert golden mole (Eremitalpa granti): a review. Journal of Comparative Psychology 116: 158-163.
This paper brings together the results of field-work on the Namib desert golden mole (Narins et al., 1997) and some of my own findings relating to its middle ear structure and function, taken from my unpublished PhD thesis. This enigmatic animal moves at night between tussocks of grass on the dunes of the Namib desert, where its prey species (mainly termites) are located. Narins et al. asked the question of whether movement between tussocks, which can be quite widely-spaced, is random, or whether this foraging is sensory-guided in some way. They concluded, based on an analysis of tracks of the mole, that the mole had some means of navigating from one tussock to the next. Eremitalpa is blind, and Narins et al. suggested that the low-frequency seismic vibrations generated as the desert wind blows through the grass could represent the cue used for navigation. Anatomically, Eremitalpa has an enormously hypertrophied malleus within its middle ear, and models of middle ear function suggest that its ossicular structure would enhance the transmission of seismic vibrations, through a form of inertial bone conduction (see Mason, 2003b). The question of how the animals could localize vibrations is briefly discussed, and two hypotheses are presented – that non-parallel axes of rotation of its ear ossicles might result in different levels of excitation in response to sound coming from one side of the animal, or that a pushed-up ridge of sand might act as a "seismic lens", enhancing detection when the mole is facing towards the source (an idea suggested by Byron Arnason).
It is worth noting that the ossicles of Eremitalpa illustrated in Figures 2 and 4 are those of the subspecies Eremitalpa granti granti. We later discovered (Mason et al., 2006) that the malleus morphology in particular is rather different in Eremitalpa granti namibensis, the subspecies that was primarily being considered in this paper. Illustrations of the intact E.g. namibensis ossicles can be found in Mason (2007) and Mason & Narins (2009).
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