4747 Introduction Magnetic compass orientation has been demonstrated in a number of vertebrate model groups including salmonids, newts, sea turtles, birds and rodents (Deutschlander et al., 2003; Gudmunsson and Sandberg, 2000; Wiltschko and Wiltschko, 1995). Both magnetite-based receptors and retinal biochemical processes have been shown to play roles in the biophysical magnetic signal transduction in birds (Wiltschko and Wiltschko, 2005). In mammalian compass orientation, Zambian Ansell’s mole-rats of the genus Fukomys (Bathyergidae) have been the model species of choice. These subterranean, microphthalmic rodents orientate themselves in their constantly dark ecotope with the help of the Earth’s magnetic field (Burda et al., 1990). However, the primary biophysical signal transduction for their light-independent polarity compass (Marhold et al., 1997a) has remained unclear. Two hypotheses are currently considered to explain the sensory mechanism of magnetic compass orientation. The first is based on retinal chemo-physical radical-pair reactions (Ritz et al., 2000), a system suggested as the primary signal transduction process for migratory birds (Ritz et al., 2004). This obviously light-dependent mechanism seems unlikely, however, for the rodent genus Fukomys, whose members spend the majority of their life underground in sealed burrow systems. A recent study has ruled out the radical-pair mechanism for this rodent (Thalau et al., 2006). The second principal hypothesis, based on a primary involvement of magnetite, seems much more reasonable for mole-rats, particularly as this mechanism is light-independent. Magnetite (Fe 3 O 4 ) has been considered a possible basis for magnetic compass orientation in diverse species (Fleissner et al., 2003; Kirschvink and Gould, 1981; Kirschvink et al., 2001; Presti and Pettigrew, 1980; Winklhofer et al., 2001). In trouts (Walker et al., 1997) and some bird species (Fleissner et al., 2003; Hanzlik et al., 2000; Williams and Wild, 2001; Winklhofer et al., 2001), clusters of tiny magnetite crystals (diameter ~1–3· m) were found in regions innervated by the ophthalmic branch of the trigeminal nerve. Physiological studies indicated that this nerve may carry magnetic field information to the brain (Beason and Semm, 1996; Mora et al., 2004). The immediate and long-term impairment of mole-rat nesting orientation induced by a magnetic pulse designed to change the magnetisation of magnetite (Marhold et al., 1997b), implicates magnetite in the signal transduction mechanism in these rodents. The highly mechano-sensitive structure of the cornea makes it a prime candidate for the location of receptors translating magnetic field information into mechanical signals. In addition to these considerations, our preliminary findings of ferrous inclusions in the corneal epithelium (Fig.·1) The mechanism of signal transduction during magnetic compass orientation is rarely evident in vertebrates and is as yet unknown in mammals. This transmission has been associated with magnetite-based receptors innervated by the ophthalmic nerve or with the involvement of the eye, particularly the retina. We provide the first behavioural support for the cornea carrying the respective primary sensors in mole-rats (Fukomys anselli) by showing that local anaesthesia disrupts their normal directional magnetic orientation. During corneal anaesthesia in normal geomagnetic conditions, mole-rats did not maintain their preferred nesting direction, but displayed a random orientation pattern. A second experiment showed that the ability of the mole-rat to discriminate between light and dark was not impeded by the same anaesthetic treatment, suggesting no retinal involvement in mole-rat magnetic orientation. Our study restricts the peripheral primary sensors in mole-rats to the ophthalmic region, probably the cornea and indicates magnetite as the responsible signal mediator. Key words: magnetic compass orientation, sensory transduction, mole-rat, cornea, magnetite, Bathyergidae. Summary The Journal of Experimental Biology 209, 4747-4750 Published by The Company of Biologists 2006 doi:10.1242/jeb.02573 Magnetic compass in the cornea: local anaesthesia impairs orientation in a mammal Regina E. Wegner*, Sabine Begall and Hynek Burda Department of General Zoology, Institute for Biology, University of Duisburg-Essen, Campus Essen, Universitätsstraße 5, 45141 Essen, Germany *Author for correspondence (e-mail: regina.wegner@uni-due.de) Accepted 2 October 2006 THE฀JOURNAL฀OF฀EXPERIMENTAL฀BIOLOGY