Magnetoreception

Monarch flying in a magnetoreception experiment. Photo credit: Jaime Rojo.

Earth's magnetic field is similar to a large bar magnet, with field lines that exit in the southern geographic hemisphere, wrap around the earth and re-enter Earth's surface in the northern hemisphere. Both inclination angle, the angle field lines make with Earth's surface, and field intensity, the strength of the field, vary predictably across the globe (top image).

The magnetic compass of monarchs relies on the tilt of field lines relative to the gravity vector. A smaller angle between the two indicates a poleward direction, which a larger angle indicates an equatorward direction. If field lines are inverted (shown on the right lower image), then the monarch's perception of north versus south changes. This induces a reversal in flight orientation.

Animals across diverse taxa, including monarchs, have the ability to detect information from Earth's magnetic field, also known as a magnetic sense. Monarchs, like many other migrating species, can derive and use this information for navigation. However, how the magnetic sense functions, from the sensor molecules to mechanisms of transduction and neural integration of information in the brain remain unknown in any animal.

Monarchs have a magnetic compass, or directional sense, that is dependent on the tilt of field lines relative to the gravity vector. When the field line direction is inverted, monarchs reverse their flight orientation (Guerra, Gegear, and Reppert, 2014).

In an attempt to use the monarch as the only genetically-tractable migratory species to uncover the molecular underpinnings of this enigmatic sense, our lab developed a new assay demonstrating that when monarchs are exposed to an inverted magnetic field, their flight activity measured by the number of wingbeat increases (see video below). Using this new assay, we demonstrated that CRYPTOCHROME1, which is light sensitive is necessary for magnetoreception, but that CRYPTOCHROME2, which is light insensitive, is not.

Whether CRYPTOCHROME1 functions as a bona fide magnetoreceptor or as part of the transduction machinery of another unknown sensor is unknown. We are currently pursuing this exciting research area using cutting-edge molecular, genetic and behavioral approaches in collaboration with a computational quantum chemist (Dr. Igor Shapiro), quantum physicist (Dr. Ronnie Rosloff), evolutionary biologist (Dr. Mickey Rosloff) and structural biologist (Dr. Hideaki Kato).

When monarchs are exposed to an inverted magnetic field (shown on the right; field inversion indicated by the red box on the timeline) they increase their wingbeats, unlike when monarchs experience the local magnetic field (shown on the left).

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