Although many animals use the Earth’s magnetic field for orientation and navigation1,2, the precise biophysical mechanisms underlying magnetic sensing have been elusive. One theoretical model proposes that geomagnetic fields are perceived by chemical reactions involving specialized photoreceptors3. However, the specific photoreceptor involved in such magnetoreception has not been demonstrated conclusively in any animal. Here we show that the ultraviolet-A/blue-light photoreceptor cryptochrome (Cry) is necessary for light-dependent magnetosensitive responses in Drosophila melanogaster. In a binary-choice behavioural assay for magnetosensitivity, wild-type flies show significant naive and trained responses to a magnetic field under full-spectrum light (∼300–700 nm) but do not respond to the field when wavelengths in the Cry-sensitive, ultraviolet-A/blue-light part of the spectrum (<420 nm) are blocked. Notably, Cry-deficient cry0 and cryb flies do not show either naive or trained responses to a magnetic field under full-spectrum light. Moreover, Cry-dependent magnetosensitivity does not require a functioning circadian clock. Our work provides, to our knowledge, the first genetic evidence for a Cry-based magnetosensitive system in any animal.
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We thank H. Zhu for the protein work in Fig. 4b, c; L. Foley for assistance; J. C. Hall for the cry0 flies; P. Emery for the Per and Cry antibodies; and P. Emery, P. Perrat, B. Leung, S. DasGupta, M. Krashes and H. Zhu for discussions. This work was supported by grants from the NIH.
Author Contributions S.M.R. and R.J.G. conceived the idea of using Drosophila to study magnetosensitivity; S.W. and R.J.G. conceived the idea of using appetitive conditioning to study magnetoresponses; R.J.G. designed the experimental apparatus; R.J.G., S.W., A.C. and S.M.R. designed the experiments and analysed the data; R.J.G. performed the experiments with help from A.C.; R.J.G., S.M.R., S.W. and A.C wrote the paper.
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Gegear, R., Casselman, A., Waddell, S. et al. Cryptochrome mediates light-dependent magnetosensitivity in Drosophila. Nature 454, 1014–1018 (2008). https://doi.org/10.1038/nature07183
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