FUNCTIONAL ALLOMETRY OF THE SEMICIRCULAR DUCTS IN SUBTERRANEAN MOLE-RATS CRYPTOMYS (BATHYERGIDAE, RODENTIA)

Background: Since the spatial mobility of subterranean mole-rats is re stricted and their skull strongly modified, morpho-functional regressi on of their vestibular organ may be expected. On the other hand, vesti bular sense may be indispensable for orientation in a world deprived o f most external sensory cues. Since vestibular sensitivity is determin ed by the size of the labyrinth, morphometrical analysis may be employ ed to assess the sensitivity and to test whether the organ is degenera te or progressively specialized. Methods: We analyzed the shape and si ze of the membranous labyrinth of vestibular organs in tote in three s pecies of African subterranean blind mole-rats of the genus Cryptomys (Bathyergidae) differing in body size yet not in habitats, ways of lif e, or employed orientation and locomotory strategies. The mechanical s ensitivity of the cupula was estimated according to Oman et al. (1987. Acta Otolaryngol. (Stockh.), 103:1-13) for each of the three semicirc ular ducts.Results: The size and shape of the vestibular organ changed predictably depending on species-specific (yet not individual) body m ass. In some aspects, particularly the cross-sectional area, the ducts were larger than expected for a mammal of a comparable body size. In all species examined, the anterior semicircular ducts exhibited the hi ghest sensitivity. Conclusions: The vestibular organs of blind subterr anean mole-rats are not regressed morpho-functionally. (C) 1994 Wiley- Liss, Inc.