title: A behavioral perspective on the biophysics of the light-dependent magnetic compass: a link between directional and spatial perception?
abstract: In terrestrial organisms, sensitivity to the Earth's magnetic field is mediated by at least two different magnetoreception mechanisms, one involving biogenic ferromagnetic crystals (magnetite/maghemite) and the second involving a photo-induced biochemical reaction that forms long-lasting, spin-coordinated, radical pair intermediates. In some vertebrate groups (amphibians and birds), both mechanisms are present; a light-dependent mechanism provides a directional sense or 'compass', and a non-light-dependent mechanism underlies a geographical-position sense or 'map'. Evidence that both magnetite- and radical pair-based mechanisms are present in the same organisms raises a number of interesting questions. Why has natural selection produced magnetic sensors utilizing two distinct biophysical mechanisms? And, in particular, why has natural selection produced a compass mechanism based on a light-dependent radical pair mechanism (RPM) when a magnetite-based receptor is well suited to perform this function? Answers to these questions depend, to a large degree, on how the properties of the RPM, viewed from a neuroethological rather than a biophysical perspective, differ from those of a magnetite-based magnetic compass. The RPM is expected to produce a light-dependent, 3-D pattern of response that is axially symmetrical and, in some groups of animals, may be perceived as a pattern of light intensity and/or color superimposed on the visual surroundings. We suggest that the light-dependent magnetic compass may serve not only as a source of directional information but also provide a spherical coordinate system that helps to interface metrics of distance, direction and spatial position.
authors.affiliation: Department of Biological Sciences, Virginia Tech, 4100 Derring Hall, Blacksburg, VA 24061-0406, USA.
authors.forename: John B
authors.initials: JB
authors.lastname: Phillips
authors.forename: Rachel
authors.initials: R
authors.lastname: Muheim
authors.forename: Paulo E
authors.initials: PE
authors.lastname: Jorge
mesh_terms: D000663:Amphibians / Q000502:physiology; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D055592:Biophysical Phenomena; D001717:Birds / Q000502:physiology; D008027:Light; D008280:Magnetics; D008954:Models, Biological; D009949:Orientation / Q000502:physiology; D012377:Rodentia / Q000502:physiology; D013037:Spatial Behavior / Q000502:physiology; D014796:Visual Perception / Q000502:physiology