Sensing Magnetic Directions in Birds: Radical Pair Processes Involving Cryptochrome

Abstract

Birds can use the geomagnetic field for compass orientation. Behavioral experiments, mostly with migrating passerines, revealed three characteristics of the avian magnetic compass: (1) it works spontaneously only in a narrow functional window around the intensity of the ambient magnetic field, but can adapt to other intensities, (2) it is an “inclination compass”, not based on the polarity of the magnetic field, but the axial course of the field lines, and (3) it requires short-wavelength light from UV to 565 nm Green. The Radical Pair-Model of magnetoreception can explain these properties by proposing spin-chemical processes in photopigments as underlying mechanism. Applying radio frequency fields, a diagnostic tool for radical pair processes, supports an involvement of a radical pair mechanism in avian magnetoreception: added to the geomagnetic field, they disrupted orientation, presumably by interfering with the receptive processes. Cryptochromes have been suggested as receptor molecules. Cry1a is found in the eyes of birds, where it is located at the membranes of the disks in the outer segments of the UV-cones in chickens and robins. Immuno-histochemical studies show that it is activated by the wavelengths of light that allow magnetic compass orientation in birds.

High levels of maternally transferred mercury disrupt magnetic responses of snapping turtle hatchlings (Chelydra serpentina)

“…The same is true for a RPM, which appears likely to play at least some role in the turtles SMA (Landler et al, 2015). The putative receptive molecule for a RPM is cryptochrome (Wiltschko and Wiltschko, 2014;Niebner et al, 2011;Liedvogel and Mouritsen, 2010;Gegear et al, 2008), a molecule best known for its role in circadian rhythms (Ye et al, 2014). The involvement of cryptochrome in the magnetic compass is consistent with most behavioral and histological evidence (Wiltschko and Wiltschko, 2014).…”

“…The putative receptive molecule for a RPM is cryptochrome (Wiltschko and Wiltschko, 2014;Niebner et al, 2011;Liedvogel and Mouritsen, 2010;Gegear et al, 2008), a molecule best known for its role in circadian rhythms (Ye et al, 2014). The involvement of cryptochrome in the magnetic compass is consistent with most behavioral and histological evidence (Wiltschko and Wiltschko, 2014). Recently, it has been shown that a zinc ion serves as a cofactor in cryptochrome photochemical reactions (Schmalen et al, 2014).…”

Lateralization of the Avian Magnetic Compass: Analysis of Its Early Plasticity

“…Interpretable magnetic information mediated by the left eye is essentially required to remove the lateralization. When the left eye system is activated, it can adjust to intensities outside the functional window of the magnetic compass (see [32]), but if it does, this ability is not transferred to the right eye system. The directional information from the magnetic field originates in the retina and is transmitted by the visual nerve to higher centers in the brain (e.g., [33][34][35].…”

“…Interpretable magnetic information mediated by the left eye is essentially required to remove the lateralization. When the left eye system is activated, it can adjust to intensities outside the functional window of the magnetic compass (see [32]), but if it does, this ability is not transferred to the right eye system.…”

Does electromagnetic therapy meet an equivalent counterpart within the organism?

“…And, because the photoreceptors are aligned in perfect hemispheres, retinae are ideal antennas. In an experiment with birds and yellow filter glasses upon their eyes, the birds had no blue light radicals anymore, and -consequently no directional information means the birds lost orientation [62].…”