Innate Directional Magnetic Preference in Drosophila melanogaster A Honors Thesis Project completed by: Natalie E. Wallace Advisors: Dr. Kristin Latham and Dr. Michael Baltzley Western Oregon University

Introduction Fruit flies (Drosophila melanogaster) are model organisms commonly used to understand genetic and behavioral mechanisms. Drosophila have been shown to be able to detect and orient to magnetic fields (Gegear et al., 2008; Phillips and Sayeed, 1993). Male and female flies may respond differently to magnetic fields (Philips and Sayeed, 1993). There are currently two proposed mechanisms of magnetoreception: the magnetite mechanism and the radial pair mechanism. http://www.yourgenome.org/stories/fruit-flies-in-the-laboratory

Magnetite Mechanism First found in magnetotactic bacteria Chains of the magnetic particle magnetite (Fe3O4) is found in specialized cells and acts like a compass needle. These chains are connected to ion channels and are triggered to open by the magnetic field, causing a change in membrane potential and starting a sensory cascade effect. http://www.sciencestockphotos.com/free/physics/slides/horseshoe_magnet.html

Radical-Pair Mechanism Radial pair mechanism is a light mediated reaction. A radial pair is a pair of molecules, each having on unpaired electron. Energy from a photon of light is absorbed by a photoreceptor, causing a chain reaction that forms the radial pair. The electrons of the radial pair can be affected by the magnetic field. In Drosophila, the cryptochrome photoreceptor is the photopigment used (Gegear et al., 2008; Gegear et al., 2010) http://www.clipartpanda.com/categories/compass-clip-art-free

Research Goals To determine whether Drosophila have an innate directional preference in response to Earth’s magnetic field. To evaluate for a difference in preference between male and female flies. http://thenode.biologists.com/wp-content/uploads/2013/10/Fly-cartoon.jpg

Experimental Set Up: Maze Pipette Tip Tube A 10 choice point Y-maze was constructed prom plastic tubing, cut pipette tips, and Y-connectors. Pipette tips made sure the flies only went one direction in the maze. One entrance point and 11 exit points. Exits were connected to food vials to encourage movement through the maze.

Experimental Set Up: Faraday Cage During trials, the maze was housed within a Faraday Cage. Faraday cages block of radio frequency (RF) fields that are emitted from electronics. This made sure that the flies were only making their choices based on the Earth’s magnetic field that can penetrate the Faraday cage.

Right/Left Controls To determine if there was a bias in the maze based on its construction, we evaluated the flies left vs. right choices. The data was organized so that: 10 = ten choices to the right 0 = zero choices to the right (all left choices) ANOVA showed no significant difference between the number of left and right choices indicating there was no bias within the maze (Figure 1). https://www.biologycorner.com/fruitflygenetics/

Right/Left Controls p > 0.5 Figure 1: A comparison of the runs with right to the north (n = 10) and right to the south (n = 10). The error bars represent the SEM for each group.

North/South Trials Used to evaluate for a north or south preference in the flies. Data was standardized to that: 10 = ten choices to the north 0 = zero choices to the north (all south choices) ANOVA showed no significant difference between the choices of the males and females. Chi-Squared test showed no significant difference from the expected value, indicating that the flies have no significant north or south preference. https://www.biologycorner.com/fruitflygenetics/

North/South Trials p > 0.1 Figure 2: A comparison of the runs with north to the right (n = 10) and north to the left (n = 10). The error bars represent the SEM for each group.

Future Directions A research study is currently underway to see if magnetic directional preference can be selected for over 15 generations in Drosophila melanogaster. Using a stronger applied magnetic field with a similar set up to this experiment may show different results. Also, using different strains of flies and/or flies collected from different geographical locations as a preference may have been selected for in the natural environment. http://www.uniprot.org/taxonomy/7227

References Gegear RJ, Casselman A, Waddell S, Reppert SM. 2008. Cryptochrome mediates light-dependent magnetosensitivity in Drosophila. Nature 454(7207):1014-1018. Gegear RJ, Foley LE, Casselman A, Reppert SM. 2010. Animal cryptochromes mediate magnetoreception by an unconventional photochemical mechanism. Nature 463(7282):804-807. Phillips JB, Sayeed O. 1993. Wavelength-dependent effects of light on magnetic compass orientation in Drosophila melanogaster. Journal of Comparative Physiology A 172(3):303-8.