Compass orientation or menotaxis is defined as the ability to orient at a specific angle relative to a directional cue. Cues used for compass orientation include the sun, stars, moon, geomagnetic field and polarized light. While there is evidence in a variety of organisms for compass orientation, the ability of mammals to use cues for compass orientation has been relatively unexplored. The goal of this research was to explore whether laboratory mice could use either magnetic or auditory cues for compass orientation. The results indicate that mice are able to learn to position their nest using a magnetic compass. The development of a magnetic compass assay in laboratory mice will allow the investigation of the mechanism of magnetic compass orientation in mammals, a goal that has been unattainable to this point.In addition, this research has provided preliminary evidence that mice are able to learn to position their nests using an auditory compass. While there is evidence in several organisms for place navigation using auditory cues (i.e. the ability to locate a specific spatial position using auditory cues), this is the first evidence in any organism for an auditory compass (i.e. the ability to calculate a directional heading relative to an auditory cue).In conclusion, both experiments provide evidence for specialized compass systems in mice and suggest that further research is necessary to fully understand the role of these systems in the behavioral ecology of mice. / Master of Science

Use of a magnetic compass has been demonstrated in all major classes of vertebrates as well as several classes of invertebrates, and is proposed to involve a photo-induced radical pair mechanism (RPM). My dissertation research consisted of characterizing a magnetic compass in a model species, Drosophila melanogaster. Preliminary experiments were carried out with adult flies, however, due to the behavioral complexity of adult responses a new behavioral assay of magnetic compass orientation was developed using larval Drosophila that elicits a robust magnetic compass response in a trained magnetic direction. This manuscript describes experiments that were conducted showing that larval magnetic compass orientation: 1) demonstrates a complex 3-dimensional pattern of response consistent with a RPM; 2) is consistent with a receptor mechanism that utilizes short- and long-wavelength antagonistic photopigments, proposed to explain wavelength dependent effects in vertebrates (e.g. amphibians and birds); and 3) produces axially symmetrical patterns of response with respect to the geomagnetic field. Additionally, tests of adult Drosophila under low and high intensities of monochromatic long wavelength light revealed a similar behavioral response to varying intensities of monochromatic light as previously reported in migratory birds (E. rubecula). These findings indicate that the magnetic compass of larval Drosophila shares a common functional architecture and similar biophysical mechanism with that of at least some vertebrates (e.g. amphibians and possibly birds), suggesting that the magnetic compass of modern vertebrates may have evolved once in a common ancestor of these three lineages over 450 million years ago. Furthermore, findings indicating a spontaneous preference for magnetic directions in D. melanogaster larvae suggest that a light-dependent magnetoreception mechanism is more widespread in insects than was previously suspected. The development of a behavioral assay to study the light-dependent magnetic compass in an organism with a simple nervous system, a limited behavioral repertoire, and with the possibility of using the full power of modern molecular and genetic techniques holds considerable promise to increase our understanding of the biophysical mechanism(s) and neurophysiological structures underlying magnetic orientation in terrestrial animals. / Ph. D.

All five classes of vertebrates use the geomagnetic field for spatial orientation. The geomagnetic field can be used to derive both 'map' and 'compass' information. There is evidence for two different mechanisms used to sense the magnetic field, the radical pair mechanism (RPM) and the magnetite based mechanism (MBM). C57BL/6 laboratory mice can rely on directional information from the magnetic field to position their nests and to solve a water maze task. The primary objective of this research was to characterize the magnetic compass of C57BL/6 laboratory mice in the plus water maze task. These experiments explored sources of variation in magnetic responses and investigated the underlying magnetic compass orientation mechanism in C57BL/6 mice. The results provide evidence that the mouse magnetic compass is sensitive to low-level radiofrequency fields, consistent with the use of the RPM for magnetic orientation. Surprisingly, the results also suggest that C57BL/6 mice have a polarity sensitive compass, consistent with the use of a MBM for magnetic orientation. These experiments confirm that mice have a specialized magnetic compass sense. Furthermore, despite the controlled environment in which these laboratory experiments were conducted, a variety of factors can increase the variability in the response. Future experiments are needed to further characterize the mouse magnetic compass, as there is a possibility of a hybrid magnetic response where both magnetoreception mechanisms could be used for spatial orientation. / Master of Science

In the 50+ years since the discovery of magnetic compass orientation by migratory songbirds, evidence for the use of magnetic cues has been obtained for a range of taxonomic groups, including several classes of vertebrate and invertebrate taxa. Surprisingly, however, the biophysical mechanisms and biological substrate that underlie magnetic sensing are still not fully understood. Moreover, while use of magnetic cues for compass orientation is intuitive, the functional significance of other forms of behavioral responses mediated by magnetic cues, such as spontaneous magnetic alignment, is less clear. The following research was carried out to investigate the mechanisms underlying magnetic orientation in vertebrates and invertebrates. This involved the modification of existing experimental systems to characterize responses to magnetic cues in laboratory animals (flies, mice) and the development of novel techniques for studying the role of magnetic cues in the spatial behavior of free-living animals (red foxes). Chapter II examines magnetic orientation in wild-type Drosophila melanogaster larvae. We show that three strains of larvae reared under non-directional ultraviolet (UV) light exhibit quadramodal spontaneous orientation along the anti-cardinal compass directions (i.e. northeast, southeast, southwest, northwest) when tested in a radially symmetrical environment under UV light. Double-blind experiments cancelling the horizontal component of the magnetic field confirmed that the response is dependent on magnetic cues rather non-magnetic features of the test environment. Furthermore, we argue that the larval quadramodal pattern of response is consistent with properties of magnetic compass orientation observed in previous studies of adult Drosophila and laboratory mice, both of which have been proposed to be mediated by a light-dependent magnetic compass mechanism. Chapter III explores the use of novel biologging techniques to collect behavioral and spatial data from free-roaming mammals. Specifically, a previous observational study of free- roaming red foxes found a 4-fold increase in the success of predatory 'mousing' attacks when foxes were facing ~north-northeast, consistent with magnetic alignment responses reported for a range of terrestrial animals. The authors propose that the magnetic field may be used to increase accuracy of mousing attacks. Using tri-axial accelerometer and magnetometer bio-loggers fitted to semi-domesticated red foxes, we created ']magnetic ethograms' from behavioral and magnetic machine learning algorithms 'trained'] to identify three discrete behaviors (i.e. foraging, trotting, and mousing-like jumps) from raw accelerometer signatures and to classify the magnetic headings of mousing-like jumps into 45° sectors from raw magnetometer data. The classifier's ability to accurately identify behaviors from a separate fox not used to train the algorithm suggests that these techniques can be used in future experiments to obtain reliable magnetic ethograms for free-roaming foxes. We also developed the first radio-frequency emitting collar that broadcasts in the low MHz frequency range shown to disrupt magnetic compass responses in a host of animals. The radio-frequency collars coupled with biologgers will provide a powerful tool to characterize magnetic alignment responses in predatory red foxes and can be adapted for use in studies of magnetic alignment and magnetic compass orientation in other free-roaming mammals. Chapter 3 discusses findings from a magnetic nest building assay involving male labratory mice. Mice trained to position nests in one of four directions relative to the magnetic field exhibited both learned magnetic compass responses and fixed magnetic nest positioning orientation consistent with northeast-southwest spontaneous magnetic alignment behavior previously reported for wild mice and bank voles. This is the first mammalian assay in which both learned magnetic compass orientation and spontaneous magnetic alignment were exhibited in the same species, and suggests that the use of magnetic cues in rodents may be more flexible that previously realized. / Ph. D. / A variety of animals have been shown to use the Earth’s magnetic field to help guide diverse spatial behaviors, however, the underlying sensory mechanisms mediating this sense remain elusive. Evidence for two distinct sensory mechanisms has come from behavioral studies involving a wide range of organisms, including migratory birds, newts, mole rats, mice, and several classes of invertebrates. The following research was carried out to determine the underlying sensory mechanisms mediating magnetic sensing in larval fruit flies. Properties consistent with a light-dependent, photoreceptor-based mechanism were found to underlie innate magnetic alignment behavior in larval flies, similar to the proposed compass mechanism thought to mediate compass responses in migratory birds and newts. A reanalysis of two previous studies of learned magnetic compass responses in adult fruit flies and laboratory mice show similar behaviors when compared to that of larval flies, suggesting a common underlying light-dependent magnetic mechanism across these groups. Furthermore, we provide evidence for learned magnetic compass responses in laboratory mice, where the orientation of individuals appears to be dependent on properties of the local environment (e.g. electromagnetic, temperature, humidity) in training and testing. These data suggest that the use of magnetic cues in mammals is context-dependent and more flexible than previously recognized. We have also developed new technologies for studies of magnetic orientation in free-roaming animals. Specifically, bio-logging devices containing triaxial accelerometer and magnetometer sensors where used to create ‘magnetic ethograms’, where the behavior and magnetic alignment of an animal can be reliably and accurately extracted from raw sensor data. We also discuss possible field experiments that can be performed to provide a specific test of the underlying sensory mechanism mediating magnetic behavior in free-roaming animals. This work will likely be of interest to a broad range of disciplines including sensory ecology, ethology, quantum chemistry, biophysics, wildlife management, and conservation.

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The ability to perceive the Earth's magnetic field has been demonstrated in a variety of animals, including representatives of all five classes of vertebrates. The physiological mechanisms underlying magnetic field sensation, however, remain largely unknown. Behavioral, physiological, neuroethological studies and studies using early response genes as neuronal activation markers indicated that a major role in the perception and processing of magnetic information play trigeminal, vestibular and visual systems. Subsequently, magnetic information seem to be integrated with multimodal sensory and motor information within the hippocampal-entorhinal system. In the majority of studies, however, birds have been used as model organisms. In this work I analyzed the neural substrate of magnetic compass orientation in the mouse strain C57BL/6J using markers c-Fos and Egr1. I found that all the aforementioned systems contain neurons responsive to the experimental magnetic fields. This finding demonstrates a complex processing of the magnetic information at level of the central nervous system.