Magnetoreception in animals

Animal Navigation is an area of science which has witnessed a vast amount of progress in the latter part of the twentieth century. A key part of its focus has been upon avian navigation, which has seen a series of recent developments published in Nature. In particular is the development of a model of navigation based upon magnetoreception.

Initially magnetoreception was thought to be solely based upon the interaction of the geomagnetic field and magnetite which is present within certain animals; in birds it is located in the beak. This was found to respond to local changes in the geomagnetic field as a result of varying crust and rock structure. This however, only provided the ‘map’ sense – just one part of navigation. It determines a position locally, but when migrating over long distances, directional information is essential, and cannot be provided through the hypothesised magnetite system direction first. Naturally there are observational clues such as celestial formations and the sun (weather permitting) from which birds can navigate.

Ritz et al. 2000, hypothesised “that magnetoreception involves radical-pair processes that are governed by anisotropic hyperfine coupling between (unpaired) electron and nuclear spins. [they showed] theoretically that fields of geomagnetic field strength and weaker can produce significantly different reaction yields for different alignments of the radical pairs with the magnetic field. As a model for a magnetic sensory organ [they] propose a system of radical pairs being 1) orientationally ordered in a molecular substrate and 2) exhibiting changes in the reaction yields that affect the visual transduction pathway. [they] evaluate threedimensional visual modulation patterns that can arise from the influence of the geomagnetic field on radical-pair systems. The variations of these patterns with orientation and field strength can furnish the magnetic compass ability of birds with the same characteristics as observed in behavioral experiments. [they] propose that the recently discovered photoreceptor cryptochrome is part of the magnetoreception system and suggest further studies to prove or disprove this hypothesis.”

A Model for Photoreceptor-Based Magnetoreception in Birds Thorsten Ritz, Salih Adem, and Klaus Schulten Biophysical Journal Volume 78 February 2000 707–718