Magnetoreception in the wood mouse (Apodemus sylvaticus): influence of weak frequency-modulated radio frequency fields

Magnetoreception in the wood mouse (Apodemus sylvaticus): influence of weak frequency-modulated radio frequency fields
Malkemper EP, Eder SH, Begall S, Phillips JB, Winklhofer M, Hart V, Burda H. Magnetoreception in the wood mouse (Apodemus sylvaticus): influence of weak frequency-modulated radio frequency fields. Sci Rep. 2015 Apr 29;4:9917. doi: 10.1038/srep09917.

Abstract

The mammalian magnetic sense is predominantly studied in species with reduced vision such as mole-rats and bats. Far less is known about surface-dwelling (epigeic) rodents with well-developed eyes. Here, we tested the wood mouse Apodemus sylvaticus for magnetoreception using a simple behavioural assay in which mice are allowed to build nests overnight in a visually symmetrical, circular arena. The tests were performed in the ambient magnetic field or in a field rotated by 90°. When plotted with respect to magnetic north, the nests were bimodally clustered in the northern and southern sectors, clearly indicating that the animals used magnetic cues. Additionally, mice were tested in the ambient magnetic field with a superimposed radio frequency magnetic field of the order of 100 nT. Wood mice exposed to a 0.9 to 5 MHz frequency sweep changed their preference from north-south to east-west. In contrast to birds, however, a constant frequency field tuned to the Larmor frequency (1.33 MHz) had no effect on mouse orientation. In sum, we demonstrated magnetoreception in wood mice and provide first evidence for a radical-pair mechanism in a mammal.
Open Access Paper: http://bit.ly/1zh1J91

ExcerptIt is widely believed that RF magnetic fields influence exclusively a radical pair mechanism, not a magnetic particle mechanism. This is certainly true for single-domain magnetite, where the inertia of the particles surrounded by the viscous cytoplasm is generally believed to hinder motion and thus transduction of oscillating fields in the radio frequency range^36, 61. However, according to Shcherbakov & Winklhofer²⁵, a magnetic particle mechanism based on magnetic susceptibility, such as the maghemite-superparamagnetic magnetite hybrid magnetoreceptor proposed by Fleissner et al.⁶² would convert the radiation into thermal agitation. As with the putative effect on a radical pair mechanism, it is not clear why such a heating effect would cause re-orientation, rather than disorientation. Importantly, however, due to the higher intensity of the Larmor frequency stimulus compared to the wideband stimulus, any heating effect would have been more pronounced for the Larmor frequency condition. Consequently, the finding of an effect of the wideband RF stimulus, but not of the higher intensity Larmor frequency stimulus, argues against a nonspecific (i.e., thermal) effect on a mechanism or process other than the radical pair mechanism.
In sum, we show that wood mice possess a magnetic sense that they use to position their nests along the NNE-SSW axis relative to the magnetic field. The NNE-SSW preference was not altered by RF fields delivered at the Larmor frequency, but was shifted by approximately 90° by a RF frequency sweep (0.9–5 MHz repeated at 1 kHz) at an intensity of only ~5% that of the Larmor frequency stimulus. The results point to the involvement of a radical pair mechanism, the first such evidence for a mammal, although further research is needed to provide a more thorough characterization of the underlying mechanism. Finally and importantly, it should be noted, that the RF magnetic fields applied here have peak intensities below the ICNIRP guidelines for general public exposure (⁶³, i.e., B_rms = 0.92 µT/f [MHz], or B_peak = 1.30 µT/f [MHz]) considered as harmless for human health. Yet, we show that they are sufficient to affect behaviour in a mammal.

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Joel M. Moskowitz, Ph.D., Director
Center for Family and Community Health
School of Public Health
University of California, Berkeley

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