Rotation of the earth’s liquid core generates a magnetic field used by many organisms to navigate their environment. While some animals such as turtles and birds use the magnetic field to engage in horizontal migrations, other organisms like magnetotactic bacteria use it to guide their migrations vertically. We find that C. elegans readily orients to artificial magnetic fields of earth strength. When assaying responses to the natural magnetic field of the earth, we found that worms appear to use the geomagnetic field to guide vertical migrations via an identified a pair of sensory neurons. Because the orientation of the geomagnetic field differs across the globe, we tested the magnetotactic ability and migratory preference of the standard lab strain (N2), and of wild-type strains isolated from different locations across the planet. We found that different populations displayed an innate preference to migrate at an angle to magnetic fields of earth-strength that would optimize their UP or DOWN direction when burrowing in their native global location. For instance, in England the geomagnetic field pierces the earth at +66 degrees (north points down). We found that well-fed British N2 worms prefer to migrate 120 degrees to an earth-strength artificial magnetic field. This seemingly arbitrary angle corresponds to the optimal angle to orient them upward when burrowing in England. By contrast, starved N2 worms migrated in the opposite direction (i.e. 300 degrees to the field), which would orient them downward in England. Consistent with natural populations adapting to local magnetic fields, we next found that worms isolated from Australia, where the geomagnetic field emanates out of the earth at -66 degrees (north points up), displayed an opposite innate pattern of migratory preference. Similar results were found for wild-type worms from Hawaii. This pattern of optimal natural variation in magnetic orientation in C. elegans serves as an excellent example to relate spatiotemporal genetic variation with a behavioral trait. The breath in number and distribution of wild-type C. elegans populations makes this a promising model for studying the effects of natural and artificial magnetic field variation on the behavior of a genetically tractable animal.
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