Abstract:
To test the hypothesis that single domain magnetite is
involved in magnetoreception, we treated Australian
silvereyes Zosterops l. lateralis with a strong, brief pulse
designed to alter the magnetization of single domain
particles. This pulse was administered in the presence of a
1 mT biasing field, either parallel to the direction of the
biasing field (PAR group) or antiparallel (ANTI group). In
the case of magnetoreceptors based on freely moving
single domain particles, the PAR treatment should have
little effect, whereas the ANTI treatment should cause
remagnetization of the magnetite particles involved in a
receptor and could produce a maximum change in that
receptor’s output for some receptor configurations.
Migratory orientation was used as a criterion to assess the
effect on the receptor. Before treatment, both groups
preferred their normal northerly migratory direction.
Exposure to the biasing field alone did not affect their
behavior. Treatment with the pulse in the presence of the
biasing field caused both the PAR and the ANTI birds to
show an axial preference for the east–west axis, with no
difference between the two groups. Although these results
are in accordance with magnetite-based magnetoreceptors
playing a role in migratory orientation, they do not
support the hypothesis that single domains in polaritysensitive
receptors are free to move through all
solid angles. Possible interpretations, including other
arrangements of single domains and superparamagnetic
crystals, are discussed.
