Guided by a “sixth sense”: unravelling magnetic migration in Monarch butterflies

• Applicant: Dr. Robin Grob
• Subject Area: Sensory and Behavioural Biology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 538064684

Each fall, millions of Monarch butterflies migrate from the Northern US and Canada over up to 5,000 km southwards to their overwintering site in Mexico. During their long journey, they employ a wide range of cues to maintain their southerly flight direction. While it has been shown that Monarch butterflies are sensitive to magnetic information, its role during migration remains elusive. In this project, I aim to behaviorally reveal the exact role of the Earth’s magnetic field during migration. Using a double-wrapped 3D-Helmoltz coil, I will study whether Monarch butterflies can use magnetic cues as a compass to keep their migratory direction (Magnetic Compass). In addition, by virtually displacing migratory Monarch butterflies, I will investigate whether they can also determine a specific goal location or even their own global position based on magnetic cues (Magnetic Map). In a second part of my project, I aim to shed light on the neural correlates of magnetic orientation in the Monarch brain. I will target candidate compass neurons within the navigation network of the central complex using multichannel tetrode recordings. I specifically aim to obtain recordings from the head-direction system during magnetic field manipulation and test how the different magnetic field components [including magnetic declination (Magnetic Compass), inclination, and field strength (Magnetic Map)] are encoded in this network. Besides compass or map, magnetic cues could also be used for compass calibration. The main compass during the Monarch butterfly’s migration is provided by skylight cues, like the position of the sun. Skylight cues, however, change their position over the course of a day. Thus, the migrating butterflies must compensate for these changes to effectively maintain their southerly migratory direction. To do so, they need a stable reference system. While time compensation is a crucial aspect of navigation, how it is established at a neuronal level remains elusive. I will investigate the role of the magnetic field as a geo-stable reference system for compass calibration. To achieve this, I will present migratory Monarch butterflies with cue conflicts, e.g., magnetic cues shifted in relation to a simulated sun. This will show whether magnetic cues provide a geo-stable reference to fine-tune the sun compass. In addition, by combining magnetic manipulations and a simulated sun stimulus, I will investigate how skylight and magnetic cues are calibrated in the navigational network of the brain. These experiments will be performed using extracellular tetrode recordings in tethered navigating butterflies, to investigate the influence of cue-conflicts on the neural coding. I aim to unravel how magnetic and celestial cues are integrated to create a time-compensated sun compass

• DFG Programme: WBP Fellowship
• International Connection: Norway
• Host: Professor Dr. Basil El Jundi