Learned magnetic map cues and two mechanisms of magnetoreception in turtles

Abstract

Overview

Growing evidence indicates that migratory animals exploit the magnetic field of the Earth for navigation, both as a compass to determine direction and as a map to determine geographical position. It has long been proposed that, to navigate using a magnetic map, animals must learn the magnetic coordinates of the destination, yet the pivotal hypothesis that animals can learn magnetic signatures of geographical areas has, to our knowledge, yet to be tested.

Findings

• An iconic navigating species, the loggerhead turtle (Caretta caretta), can learn the magnetic signatures of geographical areas.
• Juvenile turtles fed repeatedly in magnetic fields replicating specific oceanic locations learned to distinguish between magnetic fields where they encountered food and those existing elsewhere. This indicates that foraging site fidelity may be based on learned magnetic cues.
• Conditioned responses in a new magnetic map assay were unaffected by radiofrequency oscillating magnetic fields—a treatment expected to disrupt radical-pair-based chemical magnetoreception—suggesting that the magnetic map sense in turtles does not rely on this specific mechanism.
• By contrast, orientation behavior that required use of a magnetic compass was disrupted by radiofrequency oscillating magnetic fields.

Conclusion

The findings provide evidence that two different mechanisms of magnetoreception underlie the magnetic map and the magnetic compass in sea turtles. Of particular note, the study confirms that exposure to radiofrequency electromagnetic fields can disrupt certain magnetoreception-based behaviors, illustrating a direct biological link between radiofrequency fields and animal navigation mechanisms.