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Schlagwörter:
magnetoreception; magnetic compass; celestial compasses; polarized light reception; ferromagnetic particles
Zusammenfassung:
Although questions such as 'How do animals find their way, and how do they sense and process this information in the brain?' have been asked for centuries , the field of animal orientation and navigation has seen an immense leap forward in the past few decades. Moreover, our understanding has also expanded considerably regarding the molecular and physiological mechanisms of the different compasses and cues used by animals for orientation and navigation (Åkesson et al., Chapter 9, and Svensson et al., Chapter 11). Most notable are the advances made in our understanding of how animals can sense information provided by the geomagnetic field and use this information for behavioural tasks, for example for compass orientation during migration. But despite interdisciplinary and highly in-tegrative research over recent decades, we do not fully understand how animals perceive the Earth´s magnetic field. We know that animals use geomag-netic information for orientation tasks (see Åkesson et al., Chapter 9), but the receptor(s) remain to be identified. In this chapter, we review current knowledge in this area, outline challenges, and suggest future approaches to elucidate the sensory modalities used by animals for orientation and navigational tasks. 10.1 Magnetic sense Many hypotheses regarding how animals may sense the Earth's magnetic field have been proposed. Three principally different mechanisms to achieve this could theoretically be used to sense the strength of the Earth's magnetic field, including (1) induction , (2) magnetic particles, and (3) magnetically sensitive biochemical reactions. The latter two possibilities have emerged as the most promising candidate magnetoreceptor mechanisms: A light-dependent process is thought to detect the alignment of the geomagnetic field lines in space. This provides directional information that can be used for a magnetic compass (inclination compass, see Åkesson et al., Chapter 9). The other possibility is a detection process mediated by a ferromin-eral that reacts to very small changes in the direction and/or intensity of the magnetic field and, thereby, can be used as a magnetic compass and/or a magnetic positioning (map or signpost) sense (for reviews see Wiltschko and Wiltschko 1995a, 2005; Lohmann and Johnson 2000; Mouritsen and Ritz 2005). Both of the latter two mechanisms are supported by behav-ioural and physiological data in a broad range of organisms (see also Åkesson et al., Chapter 9). In some animals, like newts and birds, the presence of both mechanisms have independently been experimentally demonstrated to be present and used by the animals for different purposes, and thus are believed to be non-exclusive (Phil-lips 1986, Wiltschko and Wiltschko 1995b, and see 10.1.3). Here, we present the state-of-the-art knowledge of the sensory aspects of the two mag-netoreception mechanisms, and highlight recent advances and future challenges.
