Behavioral studies of Drosophila, amphibians and birds have provided evidence for a light-dependent magnetic compass consistent with theoretical models implicating a specialized photoreceptor in magnetoreception. To characterize the biophysical mechanism underlying the magnetic compass, we are investigating the effects of 1-20 MHz radio frequency (RF) fields on magnetic compass orientation in mice, birds and larval Drosophila. Frequencies in this range are predicted to alter magnetic field dependent energy states in a photoreceptor-based magnetoreceptor and, thus, disrupt the response of the light-dependent magnetic compass. Behavioral genetic analyses of the mechanism of magnetoreception using newly developed behavioral assays of magnetic compass orientation by larval Drosophila (Dommer et al. 2008) and inbred C57BL/6 mice (Muheim et al. 2006) are also being used to investigate the molecular basis of the magnetic compass, focusing on a newly discovered class of photopigment molecules ("cryptochromes") believed to play a role in a photoreceptor-based magnetic compass.
In related experiments with C57BL/6 mice, we are investigating the role of magnetic cues in a task traditionally used to study spatial memory in rodents (modified Morris water maze). We also have experiments underway in collaboration with colleagues at the Charles University in Prague, Czech Republic to map central pathways involved in processing magnetic stimuli in the mouse brain, retina, and trigeminal nerve system using immediate early gene expression and related neuroanatomical techniques.
Collaborative studies are being carried out with colleagues in Spain, Norway, and Australia to investigate the role of magnetic cues in the navigational map of amphibians, birds and eels. Experiments utilizing ‘simulated magnetic displacements’ are being used to investigate the magnetic field component(s) involved in a unicoordinate or bicoordinate navigational map. Related experiments have provided evidence that amphibians and birds have not one, but two, magnetoreception mechanisms. In addition to the light-dependent magnetic compass, these vertebrates have a non-light-dependent receptor involving magnetite or a similar magnetic material involved in deriving map information.
We are also investigating the integration of multiple compass systems used by migratory birds (i.e., celestial and magnetic compasses). Much of this work has focused on the possibility that polarized patterns present at sunset and/or sunrise are used as the primary calibration reference for other (sun, stars, magnetic) compass systems.