The structure of magnetiteIt’s not quite quantum physics, but in Salmon Use Sophisticated Compass Cells Brian Thomas has another sensory organ he wishes to claim could not have evolved. Curiously, it’s not all that “sophisticated” of one. The PNAS paper he talks about – the Livescience article here – is Magnetic characterization of isolated candidate vertebrate magnetoreceptor cells, which claims to provide a method to detect the presence of magnetically sensitive cells that some animals have been long-suspected of possessing. From the abstract:

In essence, a rotating magnetic field is employed to visually identify, within a dissociated tissue preparation, cells that contain magnetic material by their rotational behavior. As a tissue of choice, we selected trout olfactory epithelium [a type of tissue in the nasal cavity] that has been previously suggested to host candidate magnetoreceptor cells. We were able to reproducibly detect magnetic cells and to determine their magnetic dipole moment. […] The magnetism of the cells is due to a μm-sized intracellular structure of iron-rich crystals, most likely single-domain magnetite. In confocal reflectance imaging, these produce bright reflective spots close to the cell membrane. The magnetic inclusions are found to be firmly coupled to the cell membrane, enabling a direct transduction of mechanical stress produced by magnetic torque acting on the cellular dipole in situ. Our results show that the magnetically identified cells clearly meet the physical requirements for a magnetoreceptor capable of rapidly detecting small changes in the external magnetic field.

Salmon, trout – same thing. For some videos of cells merrily spinning around as part of this experiment, see here. Continue reading