Markéta Kvíčalová

Cryptochrome 2 mediates directional magnetoreception in cockroaches

Significance The photosensitive protein Cryptochrome (Cry) is involved in the detection of magnetic fields (MFs) in Drosophila. However, Cry-dependent responses to natural MF intensities and to the direction of the MF vector have not been demonstrated previously in any insect. Birds, monarch butterflies, and many other species perceive the direction of geomagnetic field (GMF) lines, but the involvement of Cry has not been rigorously proven using genetic tools. In this study, by combining behavioral and genetic approaches, we provide the first unambiguous evidence to our knowledge of a Cry-dependent sensitivity to the direction of GMF in two cockroach species. Furthermore, by eye-covering experiments and by immunolocalization of a crucial mammalian-type Cry2 under the retina, we clearly show that the eye is an indispensable organ for the directional GMF response. The ability to perceive geomagnetic fields (GMFs) represents a fascinating biological phenomenon. Studies on transgenic flies have provided evidence that photosensitive Cryptochromes (Cry) are involved in the response to magnetic fields (MFs). However, none of the studies tackled the problem of whether the Cry-dependent magnetosensitivity is coupled to the sole MF presence or to the direction of MF vector. In this study, we used gene silencing and a directional MF to show that mammalian-like Cry2 is necessary for a genuine directional response to periodic rotations of the GMF vector in two insect species. Longer wavelengths of light required higher photon fluxes for a detectable behavioral response, and a sharp detection border was present in the cyan/green spectral region. Both observations are consistent with involvement of the FADox, FAD•− and FADH– redox forms of flavin. The response was lost upon covering the eyes, demonstrating that the signal is perceived in the eye region. Immunohistochemical staining detected Cry2 in the hemispherical layer of laminal glia cells underneath the retina. Together, these findings identified the eye-localized Cry2 as an indispensable component and a likely photoreceptor of the directional GMF response. Our study is thus a clear step forward in deciphering the in vivo effects of GMF and supports the interaction of underlying mechanism with the visual system.

American cockroaches prefer four cardinal geomagnetic positions at rest.

A specific behavior based on the ability to perceive the magnetic field has been described in several species: when resting or grazing animals take up a position placing their main body axis parallel with the North-South or East-West geomagnetic axes, which is referred to as magnetic alignment. The adaptive significance of this behavior remains an enigma. No experiments have been made to date to demonstrate conclusively whether that orientation will adequately change in response to an experimental rotation of geomagnetic axes which is a key step to prove the use of exclusively magnetic cues for orientation. In our study, we identified a preference regarding the four cardinal magnetic axes, i.e. a quadrimodal alignment both in natural and in 60deg rotated fields. The study gives the original evidence that quadrimodal alignment is a type of animal behavior specifically related to the cardinal magnetic axes of the Earth.