Physical and Chemical Principles of Magnetosensation in Biology

This chapter provides an overview of the recent progress in elucidating the physical basis of geomagnetic-field sensitivity in higher organisms. Following a brief introduction to the behavioral evidence, two hypotheses on the magneto-reception mechanism are discussed, both of which are physically plausible and in agreement with behavioral experiments. Under the radical-pair hypothesis, an external magnetic field will interfere with the dynamics of singlet-triplet intercon-version in a spin-correlated radical pair (RP) and, hence, change the ratio between singlet and triplet products created from the RP (biochemical compass). The magnetite hypothesis, on the other hand, posits that biogenic magnetite found in nerve tissue converts the external magnetic field into a mechanical stimulus. A brief overview is also provided of non-destructive techniques suitable to screen tissue samples for the presence of magnetite or other iron mineral phases, which usually is the first step in identifying magnetoreceptors and studying magnetite biomineralization.