Magnetic field effects on Drosophila melanogaster and avian cryptochromes

One of the major challenges in the field of sensory biology is to understand the process by which migratory songbirds sense the direction of the Earth’s magnetic field. This phenomenon, which has fascinated biologists for decades, has seen a growth of interest in the recent years. This poorly understood “sixth sense” has focused the attention of scientists from a variety of disciplines, from biology to theoretical physics. This multidisciplinarity is reflected in the work presented in this thesis, which spans animal behaviour, biochemistry, and spectroscopy. The common thread that links these experiments is the need to gain a better understanding of the radical pair mechanism of magnetoreception. According to this hypothesis, animals perceive magnetic fields by means of magnetically sensitive radicals formed by light-excitation of photosensitive flavoproteins called cryptochromes. The first project, presented in Chapter 2, was an investigation of magnetic field effects on Drosophila melanogaster negative geotaxis. Two sets of equipment were built, experiments were conducted in a meticulously controlled environment, and strong statistical tests were applied to a large-scale dataset, but it proved impossible to reproduce the magnetic field effects reported in the literature. The second project, presented in Chapter 3, was to test whether avian cryptochromes 1a and 1b could be the magnetoreceptor molecules. The proteins were expressed and purified and their binding affinity for flavin adenine dinucleotide, the chromophore responsible for light activation of the protein, was determined. It was concluded that cryptochromes 1a and 1b cannot be the magnetoreceptors, even though they have been considered ideal candidates for many years. Finally, the third project, described in Chapter 4, was a comparative study of the spectroscopic properties and magnetic sensitivity of avian cryptochrome 4s from different species using Broadband Cavity-Enhanced Absorption Spectroscopy. This technique has the advantage of detecting the change in the optical absorbance of photo-induced radicals when the proteins are exposed to an external magnetic field. Striking differences were found between cryptochrome 4s from migratory and non-migratory birds.