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The quantum needle of the avian magnetic compass

  1. P. J. Horea,2
  1. aDepartment of Chemistry, Physical & Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom;
  2. bInstitut für Biologie und Umweltwissenschaften, Carl von Ossietzky Universität Oldenburg, 26111 Oldenburg, Germany;
  3. cResearch Centre for Neurosensory Sciences, University of Oldenburg, 26111 Oldenburg, Germany

  1. Edited by Michael L. Klein, Temple University, Philadelphia, PA, and approved March 1, 2016 (received for review January 8, 2016)

Significance

Billions of birds fly thousands of kilometers every year between their breeding and wintering grounds, helped by an extraordinary ability to detect the direction of the Earth’s magnetic field. The biophysical sensory mechanism at the heart of this compass is thought to rely on magnetically sensitive, light-dependent chemical reactions in cryptochrome proteins in the eye. Thus far, no theoretical model has been able to account for the <5° precision with which migratory birds are able to detect the geomagnetic field vector. Here, using computer simulations, we show that genuinely quantum mechanical, long-lived spin coherences in realistic models of cryptochrome can provide the necessary precision. The crucial structural and dynamical molecular properties are identified.

Abstract

Migratory birds have a light-dependent magnetic compass, the mechanism of which is thought to involve radical pairs formed photochemically in cryptochrome proteins in the retina. Theoretical descriptions of this compass have thus far been unable to account for the high precision with which birds are able to detect the direction of the Earth's magnetic field. Here we use coherent spin dynamics simulations to explore the behavior of realistic models of cryptochrome-based radical pairs. We show that when the spin coherence persists for longer than a few microseconds, the output of the sensor contains a sharp feature, referred to as a spike. The spike arises from avoided crossings of the quantum mechanical spin energy-levels of radicals formed in cryptochromes. Such a feature could deliver a heading precision sufficient to explain the navigational behavior of migratory birds in the wild. Our results (i) afford new insights into radical pair magnetoreception, (ii) suggest ways in which the performance of the compass could have been optimized by evolution, (iii) may provide the beginnings of an explanation for the magnetic disorientation of migratory birds exposed to anthropogenic electromagnetic noise, and (iv) suggest that radical pair magnetoreception may be more of a quantum biology phenomenon than previously realized.

Footnotes

  • ↵1H.G.H. and S.W. contributed equally to this work.

  • ↵2To whom correspondence should be addressed. Email: peter.hore{at}chem.ox.ac.uk.

  • Author contributions: P.J.H. designed research; H.G.H., S.W., D.R.K., C.S., and Y.J. performed research; D.E.M., H.M., and P.J.H. wrote the paper; and C.S. and Y.J. performed preliminary calculations.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1600341113/-/DCSupplemental.

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