BOLES, L.C.*; LOHMANN, K.J.: The effects of attached magnets on the orientation of displaced spiny lobsters

Many animals use the Earth�s magnetic field as a cue during orientation and navigation. However, relatively little is known about how these animals, particularly invertebrates, actually detect magnetic fields. Spiny lobsters, Panulirus argus have a magnetic compass sense and display homeward orientation in the laboratory after long distance (>10 km) displacements. In order to evaluate the role of the Earth�s magnetic field in this behavior and to localize the site of magnetic field reception, we used small permanent magnets to disturb the magnetic field in different regions of the lobster�s body. Magnets were attached in one of three locations: (1) between the rostral horns just above the eyestalks, (2) on the ventral cephalothorax between the fourth and fifth walking legs, and (3) on the dorsal side of the last abdominal segment. Non-magnetic brass bars were placed in the two positions lacking a magnet. Based on current theories, each location represented a potential site of magnetic field reception due to the presence of either photoreceptors or permanently magnetic material in adjacent tissues. The ability of lobsters with attached abdominal magnets to correctly orient in the homeward direction suggests that magnetic field reception does not occur in the posterior portion of the body. However, magnets placed near the eyes or on the ventral cephalorthorax did disrupt the homeward orientation of displaced lobsters. These results will be discussed in relation to current theories of magnetic field reception and in light of previous studies of magnetic orientation in lobsters.