Spontaneous magnetic orientation in larval Drosophila shares properties with learned magnetic compass responses in adult flies and mice.

We provide evidence for spontaneous quadramodal magnetic orientation in a larval insect. Second instar Berlin, Canton-S and Oregon-R × Canton-S strains of Drosophila melanogaster exhibited quadramodal orientation with clusters of bearings along the four anti-cardinal compass directions (i.e. 45, 135, 225 and 315 deg). In double-blind experiments, Canton-S Drosophila larvae also exhibited quadramodal orientation in the presence of an earth-strength magnetic field, while this response was abolished when the horizontal component of the magnetic field was cancelled, indicating that the quadramodal behavior is dependent on magnetic cues, and that the spontaneous alignment response may reflect properties of the underlying magnetoreception mechanism. In addition, a re-analysis of data from studies of learned magnetic compass orientation by adult Drosophila melanogaster and C57BL/6 mice revealed patterns of response similar to those exhibited by larval flies, suggesting that a common magnetoreception mechanism may underlie these behaviors. Therefore, characterizing the mechanism(s) of magnetoreception in flies may hold the key to understanding the magnetic sense in a wide array of terrestrial organisms.

Magnetic compass orientation by larval Drosophila melanogaster.

We report evidence for magnetic compass orientation by larval Drosophila melanogaster. Groups of larvae were exposed from the time of hatching to directional ultraviolet (365nm) light emanating from one of four magnetic directions. Larvae were then tested individually on a circular agar plate under diffuse light in one of four magnetic field alignments. The larvae exhibited magnetic compass orientation in a direction opposite that of the light source in training. Evidence for a well-developed magnetic compass in a larval insect that moves over distances of at most a few tens of centimeters has important implications for understanding the adaptive significance of orientation mechanisms like the magnetic compass. Moreover, the development of an assay for studying magnetic compass orientation in larval D. melanogaster will make it possible to use a wide range of molecular genetic techniques to investigate the neurophysiological, biophysical, and molecular mechanisms underlying the magnetic compass.

Shedding light on vertebrate magnetoreception.

We review the challenges and recent progress in elucidating the physiological basis of animal magnetoreception. Behavioral and theoretical studies suggest a link between photoreception and magnetoreception in some animals. Neurophysiological studies have the potential to prove this link and identify the location of and the mechanism underlying the magnetoreception system.