The magnetic sense of honey bees - analyses of underlying mechanisms and potential function

I studied a potential function and underlying mechanism(s) of the magnetic sense in honey bees, Apis mellifera. A waggle-dancing bee informs hive mates about a food source. Directional information pointing to the food source relative to the sun's azimuth is encoded in the angle between the straight segment of her waggle dance and a reference line such as gravity or the local geomagnetic field (LGMF). Neither cancelling the LGMF nor shifting its declination affected the recruitment success of waggle-dancing bees, implicating gravity as the reference line for the dance alignment. To study the underlying mechanism(s) of the bees’ magnetic sense, I analyzed lyophilized and pelletized bee tagmata by a Superconducting Quantum Interference Device. A distinct hysteresis loop for the abdomen but not for the thorax or the head of bees indicated the presence of magnetite in the abdomen. Magnetic remanence of abdomen pellets produced from bees that I did, or did not, expose to an NdFeB magnet while alive differed, indicating that magnet-exposure altered the magnetization of this magnetite in live bees. Following exposure of live bees to the same magnet, magnetized bees, unlike sham-treated control bees, failed to sense the presence of a magnetic anomaly, demonstrating a functional connection between magnetite in the abdomen and the magnetoreceptor, and temporary or permanent disablement of the receptor through magnet-exposure. To test whether bees sense the polarity of a magnetic field, I trained bees to associate a magnetic anomaly with a sugar water reward. I then presented trained bees with a sugar water reward in two separate watch glasses, placing one reward in the center of the anomaly that I either kept the same as during bee training (control experiment) or that I altered by reversing its polarity (treatment experiment). That bees continued to recognize the magnetic anomaly when its polarity was kept unaltered, but failed to recognize it when its polarity was reversed, indicates that bees have a polarity-sensitive magnetoreceptor. To increase the detectability of magnetite in bee tissues, I lyophilized samples to reduce water content, maximized the signal amplitude by pelletizing samples, and accounted for sample dimensions in data analyses.