The Physics of Geomagnetic-Field Transduction in Animals.
In: IEEE Transactions on Magnetics, Vol. 45, No. 12: pp. 5259-5265
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Birds, fish, sea turtles, and various other animals have been reportedto sense the geomagnetic field and to use it for orientation,navigation, and homing. In recent years, exciting progress has been madetowards elucidating the physical and structural basis of this remarkablephenomenon. This paper focuses on the two hypotheses that drive currentresearch into magnetoreception. One proposal relies on the presence ofmolecules that undergo magnetically anisotropic chemical reactions dueto transient formation of a radical pair. The proposedmechanism-essentially a chemical compass-is theoreticallywell-established and specifically designed behavioral experiments mayindeed be interpreted that way, which has sparked a hunt for themolecules and structures in question. The ferrimagnetic transductionhypothesis, on the other hand, draws its plausibility from boththeoretical considerations and the fact that magnetite has been detectedin sensory neurons, with stable single-domain particles in fish andmicrometer-scale clusters of superparamagnetic nanocrystals in birds. Wediscuss the limitations of our current knowledge and suggest futurestudies.