Two recent papers have been published on magnetoreception in birds. In this case it is the ability of the birds to sense the direction of the Earth's magnetic field potentially for navigation.
- Expression patterns of cryptochrome genes in avian retina suggest involvement of Cry4 in light-dependent magnetoreception Atticus Pinzon-Rodriguez, Staffan Bensch, Rachel Muheim J. R. Soc. Interface 2018 15 20180058; DOI: 10.1098/rsif.2018.0058. Published 28 March 2018
- Double-Cone Localization and Seasonal Expression Pattern Suggest a Role in Magnetoreception for European Robin Cryptochrome 4 Günther, Anja et al. Current Biology , Volume 28 , Issue 2 , 211 - 223.e4
The idea has been around a long time; cf A Biomagnetic Sensory Mechanism Based on Magnetic Field Modulated Coherent Electron Spin Motions Zeitschrift fur Physikalishe Chemie Neue Folge, Bd. 111, S. 1-5, (1978)
The two new papers address the role of something called "radical pairs", two molecules, each with an unpaired electron. The large molecules are in the retina and tend to have a preferred orientation with respect to the curved retina, and they also appear to affect the perceived intensity of blue light. This causes a modulation of light sensitivity across the retina dependent on the direction of the magnetic field with respect to the direction of the local normal vector of the retina.
The modulation of the reaction rate by the magnetic field direction has to do with singlet vs triplet states and quantum coherence, but I only say that because I've tried to read Cryptochrome and Magnetic Sensing by the Theoretical and Computational Biophysics Group at U. Illinois, Urbana-Champagne, as well as this Science Alert.
Are there simpler examples of the sensitivity of the reaction rate of "radical pairs" to the orientation of a magnetic field? Perhaps two atoms or two small molecules? Or does this phenomenon generally occur only in large, complex molecules?