Biogenic magnetite and magnetic sensitivity in organisms -- from magnetic bacteria to pigeons

M. Winklhofer

Department of Earth and Environmental Science, University of Munich, 41/IV Theresienstr., D-80333 Munich, Germany

Abstract
A large number of animals across all major animal phyla use the Earth's magnetic field for orientation, long-distance migration and homing (see \cite{WiltschkoWiltschko:95}, for a review of the behavioural evidence). Despite three decades of research in the field, astonishingly little is known about the nature of the underlying magnetic sense, the main reason for its elusiveness being that magnetic sensory cells -- the postulated morphological correlates of the magnetoreceptor -- have not yet been identified with certainty. It was only in the last five years that candidate magnetoreceptor cells have been detected, on which hypothesis can now be tested and specific theoretical models be elaborated to answer the following questions: What is the nature of magnetic sensory cells? By what physical mechanism is the external magnetic field coupled into the organism (reception)? How sensitive is the mechanism to small changes in the magnetic field (detection threshold) ? What physical mechanisms or chemical pathways convert the received magnetic energy into a nervous signal (transduction)? Figs 3, Refs 40.