title: Light-dependent magnetoreception in birds: the crucial step occurs in the dark.
abstract: The Radical Pair Model proposes that the avian magnetic compass is based on spin-chemical processes: since the ratio between the two spin states singlet and triplet of radical pairs depends on their alignment in the magnetic field, it can provide information on magnetic directions. Cryptochromes, blue light-absorbing flavoproteins, with flavin adenine dinucleotide as chromophore, are suggested as molecules forming the radical pairs underlying magnetoreception. When activated by light, cryptochromes undergo a redox cycle, in the course of which radical pairs are generated during photo-reduction as well as during light-independent re-oxidation. This raised the question as to which radical pair is crucial for mediating magnetic directions. Here, we present the results from behavioural experiments with intermittent light and magnetic field pulses that clearly show that magnetoreception is possible in the dark interval, pointing to the radical pair formed during flavin re-oxidation. This differs from the mechanism considered for cryptochrome signalling the presence of light and rules out most current models of an avian magnetic compass based on the radical pair generated during photo-reduction. Using the radical pair formed during re-oxidation may represent a specific adaptation of the avian magnetic compass.
authors.affiliation: FB Biowissenschaften, Goethe-Universität Frankfurt, Max-von-Laue-Straße 13, 60438 Frankfurt am Main, Germany wiltschko@bio.uni-frankfurt.de.
authors.forename: Roswitha
authors.initials: R
authors.lastname: Wiltschko
authors.affiliation: Université Pierre et Marie Curie, Casier 156, 4 Place Jussieu, 75005 Paris, France.
authors.forename: Margaret
authors.initials: M
authors.lastname: Ahmad
authors.affiliation: FB Biowissenschaften, Goethe-Universität Frankfurt, Max-von-Laue-Straße 13, 60438 Frankfurt am Main, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Nießner
authors.affiliation: FB Biowissenschaften, Goethe-Universität Frankfurt, Max-von-Laue-Straße 13, 60438 Frankfurt am Main, Germany.
authors.forename: Dennis
authors.initials: D
authors.lastname: Gehring
authors.affiliation: FB Biowissenschaften, Goethe-Universität Frankfurt, Max-von-Laue-Straße 13, 60438 Frankfurt am Main, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wiltschko
mesh_terms: D000818:Animals; D001717:Birds / Q000502:physiology*; D056931:Cryptochromes / Q000378:metabolism*; D008027:Light; D060526:Magnetic Fields; D010465:Perception / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D056931:Cryptochromes
keywords: avian magnetic compass; cryptochrome 1a; flavin redox cycle; light-activation; radical pairs