Several groups of mammals use the Earth's magnetic field for orientation, but their magnetosensory organ remains unknown. The Ansell's mole-rat (Fukomys anselli, Bathyergidae, Rodentia) is a microphthalmic subterranean rodent with innate magnetic orientation behaviour. Previous studies on this species proposed that its magnetoreceptors are located in the eye. To test this hypothesis, we assessed magnetic orientation in mole-rats after the surgical removal of their eyes compared to untreated controls. Initially, we demonstrate that this enucleation does not lead to changes in routine behaviours, including locomotion, feeding and socializing. We then studied magnetic compass orientation by employing a well-established nest-building assay under four magnetic field alignments. In line with previous studies, control animals exhibited a significant preference to build nests in magnetic southeast. By contrast, enucleated mole-rats built nests in random magnetic orientations, suggesting an impairment of their magnetic sense. The results provide robust support for the hypothesis that mole-rats perceive magnetic fields with their minute eyes, probably relying on magnetite-based receptors in the cornea.

Department of Game Management and Wildlife Biology Faculty of Forestry and Wood Sciences Czech University of Life Sciences 16521 Prague 6 Czech Republic

Department of General Zoology University of Duisburg Essen Universitaetsstr 5 45117 Essen Germany

Department of Zoology Faculty of Science Charles University Vinicna 7 12844 Prague Czech Republic

Department Vision Visual Impairment and Blindness Faculty 13 Technical University of Dortmund Emil Figge Straße 50 44227 Dortmund Germany

Max Planck Research Group Neurobiology of Magnetoreception Center of Advanced European Studies and Research Ludwig Erhard Allee 2 53175 Bonn Germany

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