Magnetic Sensitivity and its Possible Physical Basis in the Yellowfin Tuna, Thunnus Albacares

Abstract

Many animals are known to orient to magnetic fields. However, two central problems in the study of magnetic sensitivity have been the almost complete failure of magnetic field conditioning experiments and the lack of avidence for a feasible transduction mechanism. In the studies reported here, yellowfin tuna learned to discriminate between two earth-strength magnetic fields in a discrete-trials/fixed interval conditioning procedure. Magnetometry experiments, diffraction spectra and electron microscope analyses demontrated single-domain cristals of the ferromagnetic mineral magnetite in the head of this species. The cristals are concentrated in tissue contained within a sinus formed by the ethmoid bones of the skull. Theoretical analyses show that the cristals would be suitable for use in magnetoreception if linked to the nervous system. The physical properties of the cristal would determine the operation of the magnetic sense. Tests of these constraints in appropriately designed conditionning experiments will provide powerful tests of the ferro-magnetic magnetoreception hypothesis