|A large variety of animals possess a magnetic sense. Migratory
birds use magnetic clues (in addition to light polarization, star signs,
position of the sun) to find their way south in fall and north in spring.
Salamanders and newts use the geomagnetic field for orientation when they
have to find the direction of the nearest shore quickly, e.g., when they
sense danger. Behavioral experimentalists have used these natural movement
patterns to design experiments that allow them to investigate in which
way geomagnetic information is used for orientation.
Although the use of the geomagnetic field for directional information
is well established experimentally, it is not known by which biophysical
mechanism magnetoreception is achieved. The magnetic sense is maybe the
last perception mechanism for which the nature of the receptors and of
the underlying biophysical mechanism remain unknown. Of the many mechanisms
proposed, only two have been supported by theoretical analysis and experimental
evidence, namely the use of ferromagnetic material (magnetite) and a chemical
detection mechanism based on the sensitivity of a class of chemical reactions
- radical-pair reactions - to weak magnetic fields.
Understanding the physical basis of the radical pair mechanism is an
intriguing problem that can be addressed theoretically through solving
the relevant quantum mechanical equations (stochastic Liouville equation)
for a given radical-pair system. Based on such calculations, we have suggested
a model for a chemical compass that can
explain experimental observations.
We are currently interested in testing the chemical compass hypothesis.
can one determine whether the magnetic compass of animals is based on a
radical pair mechanism? Quantum physical calculations show that oscillating
magnetic fields in the radio frequency (RF) range can change radical pair
reactions and, thus, would disturb a compass based on such reactions. An
animal should therefore show a change in its magnetic orientation behavior
when it is exposed to RF fields. Together with behavioral biologists we
work on designing such an earth-field magnetic resonance experiment on
the basis of existing behavioral assays.