A Cryptic Response?

Abstract

Newts, bees, migratory birds, and various other animals detect Earth’s magnetic field, which can provide cues used in orientation and navigation. One mechanism proposed to underlie this ability involves the modulation by a magnetic field of a chemical reaction initiated through light absorption by a photoreceptor. Gegear et al . investigated the role of cryptochrome--which in Drosophila is a photoreceptor sensitive to ultraviolet-A and blue light that functions to reset the circadian clock--in fruit fly magnetoreception. Using a behavioral assay in which flies could choose to enter either an arm of a T-maze in which they experienced a magnetic field or an arm in which no field was generated, the authors analyzed the responses of naive and trained flies. Whereas only some strains of flies showed a naive response to a magnetic field (avoidance), all strains tested preferred the arm with the magnetic field after being trained to associate the magnetic field with a sucrose reward. However, neither naive nor trained flies showed a preference when short-wavelength (ultraviolet-A and blue) light was blocked. Moreover, mutant flies that lacked cryptochrome failed to show either naive or trained responses to the presence of a magnetic field. In contrast, disruption of circadian clock function through exposure to constant light failed to abolish behavioral response to a magnetic field. Thus, cryptochrome appears to play a critical role in Drosophila magnetoreception. Rouyer provides commentary, noting that it is not clear why fruit flies (which don’t migrate) need to perceive Earth’s magnetic field. R. J. Gegear, A. Casselman, S. Waddell, S. M. Reppert, Cryptochrome mediates light-dependent magnetosensitivity in Drosophila . Nature 454 , 1014-1018 (2008). [PubMed] F. Rouyer, Mutant flies lack magnetic sense. Nature 454 , 949-951 (2008). [PubMed]