Light-independent and pulsing-sensitive magnetic compass responses in planarians

Many animals can sense the Earth's magnetic field and use it for orientation. However, the mechanism underlying magnetoreception has not been identified, partially due to the lack of reproducible and genetically tractable model systems. Here, we establish a directional assay for planaria to test their responses to different magnetic fields. Girardia dorotocephala showed a preferred magnetic directionality in the horizontal plane in an Earth-strength magnetic field in the absence of visible light, which shifted if the azimuth was rotated and was absent when the magnetic field was cancelled. This directional preference differed between labs. Furthermore, the directional response was affected by a short but strong magnetic pulse, resulting in a random distribution. The effect of the pulse was temporary, with directional preferences recovering over several days. Taken together, these data are consistent with a magnetoreception mechanism in planarians that functions independently of light and relies on permanently magnetised material, such as single-domain magnetite. As planarians are genetically tractable and well-established, they are a promising invertebrate model organism that might offer insights into the mechanisms underlying magnetoreception in animals.