Magnetic field detection is distinct from light detection in the invertebrates Tenebrio and Talitrus

Abstract

THE mechanism used by animals for geomagnetic field detection has long been discussed¹. Leask² has proposed that sensitivity to magnetic field might result from polarised light detection through optical pumping into the lowest level triplet state of (say) the rhodopsin molecule that possesses spin. Light detection, he suggests, might be a prerequisite for magnetic field detection and might result in an axial rather than a polar response in the animal. However, a unimodal reaction has been found³ with Tenebrio molitor L., the flour-beetle, in a horizontally directed magnetic field and a light field without directional features. This result was obtained when Tenebrio had been allowed to associate the geomagnetic field with the directional properties of the anisotropic light field in the culture container. The preferential direction in the horizontally directed magnetic field could be predicted from the ‘dark direction’ and from the relative humidity in the container (ref. 3, expt 43, page 429). I report here that Tenebrio and Talitrus saltator Mont., the sandhopper, can orientate in the Earth's magnetic field in complete darkness, and that in Tenebrio this orientation is essentially polar, not axial. These results are evidence that these two invertebrates do not require light for the detection of the magnetic field.