3649 INTRODUCTION Diverse animals, including birds, mammals, reptiles, amphibians, fish, crustaceans and insects, use the Earth’s magnetic field for directional orientation and navigation (Wiltschko and Wiltschko, 1995; Wiltschko and Wiltschko, 2005; Lohmann et al., 2007). Despite the remarkable progress that has been accomplished during the past decade, evidence for magnetoreception in mammals remains fairly limited. Magnetic compass orientation has been convincingly demonstrated in only two species of distantly related subterranean rodents (Burda et al., 1990; Kimchi and Terkel, 2001), two epigeic rodent species (Deutschlander et al., 2003; Muheim et al., 2006) and three bat species (Holland et al., 2006; Holland et al., 2010; Wang et al., 2007). More recently, magnetic alignment has been demonstrated in larger mammals, namely cattle and deer (Begall et al., 2008; Begall et al., 2011; Burda et al., 2009), and in hunting foxes (Cerveny et al., 2011). Likewise, the mechanisms of magnetoreception in mammals have been less studied than those of other vertebrates (Johnsen and Lohmann, 2005; Mouritsen and Ritz, 2005; Nemec et al., 2005). Indeed, except for two recent papers providing evidence for a magnetite-based polarity compass in bats (Wang et al., 2007; Holland et al., 2008), our current knowledge about the underlying mechanisms comes from the study of a single subterranean species – Ansell’s mole-rat, Fukomys anselli. Ansell’s mole-rat has proved to be an excellent model with which to investigate magnetic orientation because of its robust, spontaneous drive to construct nests in the southeastern sector of a circular arena using magnetic field azimuth as the primary orientation cue (Burda et al., 1990). In marked contrast to birds (Ritz et al., 2010), its magnetic compass is light independent, polarity based and insensitive to magnetic fields oscillating in the MHz range (Marhold et al., 1997a; Marhold et al., 1997b; Thalau et al., 2006). However, a brief magnetic pulse designed to alter the magnetization of single- domain magnetite can lead to a long-term (≥3 months) deflection of mole-rat directional preference (Marhold et al., 1997b). Together, these functional properties strongly suggest that the mole-rat possesses a magnetite-mediated compass. It is also the only mammalian species in which the neural basis of magnetic orientation has been analyzed. It has been shown that magnetic information is integrated with multimodal sensory and motor information into a common spatial representation of allocentric space within the superior colliculus, the head direction system and the entorhinal–hippocampal spatial representation system (Nemec et al., 2001; Burger et al., 2010). Although magnetoreceptors remain unknown, recent experiments involving anaesthesia of the eye have suggested the cornea to be a candidate receptor site (Wegner et al., 2006a). The adaptive significance of magnetic orientation in the underground ecotope seems to be obvious (Moritz et al., 2007). In a dark world deprived of most of the sensory cues that are normally available aboveground, the Earth’s magnetic field provides the only SUMMARY Evidence for magnetoreception in mammals remains limited. Magnetic compass orientation or magnetic alignment has been conclusively demonstrated in only a handful of mammalian species. The functional properties and underlying mechanisms have been most thoroughly characterized in Ansellʼs mole-rat, Fukomys anselli, which is the species of choice due to its spontaneous drive to construct nests in the southeastern sector of a circular arena using the magnetic field azimuth as the primary orientation cue. Because of the remarkable consistency between experiments, it is generally believed that this directional preference is innate. To test the hypothesis that spontaneous southeastern directional preference is a shared, ancestral feature of all African mole-rats (Bathyergidae, Rodentia), we employed the same arena assay to study magnetic orientation in two other mole-rat species, the social giant mole-rat, Fukomys mechowii, and the solitary silvery mole-rat, Heliophobius argenteocinereus. Both species exhibited spontaneous western directional preference and deflected their directional preference according to shifts in the direction of magnetic north, clearly indicating that they were deriving directional information from the magnetic field. Because all of the experiments were performed in total darkness, our results strongly suggest that all African mole-rats use a light- independent magnetic compass for near-space orientation. However, the spontaneous directional preference is not common and may be either innate (but species-specific) or learned. We propose an experiment that should be performed to distinguish between these two alternatives. Supplementary material available online at http://jeb.biologists.org/cgi/content/full/215/20/3649/DC1 Key words: spatial orientation, magnetic sense, magnetoreception, mole-rat, Bathyergidae, Fukomys, Heliophobius. Received 18 December 2011; Accepted 10 July 2012 The Journal of Experimental Biology 215, 3649-3654 © 2012. Published by The Company of Biologists Ltd doi:10.1242/jeb.069625 RESEARCH ARTICLE Magnetic compass orientation in two strictly subterranean rodents: learned or species-specific innate directional preference? Ludmila Oliveriusová 1 , Pavel Nemec 2, *, Zuzana Králová 2 and Frantisek Sedlácek 1 1 Department of Zoology, Faculty of Science, University of South Bohemia, CZ-370 05 Ceske Budejovice, Czech Republic and 2 Department of Zoology, Faculty of Science, Charles University in Prague, CZ-128 44 Praha 2, Czech Republic *Author for correspondence (pgnemec@natur.cuni.cz) THE฀JOURNAL฀OF฀EXPERIMENTAL฀BIOLOGY