Antennal Circadian Clocks Coordinate Sun Compass Orientation in Migratory Monarch Butterflies

Abstract

Butterfly Navigation: Monarch butterflies migrate to Mexico from various parts of North America in the fall and navigate with the aid of Sun compass. This navigational mechanism, also employed by migratory birds, uses the circadian clock to compensate for the positional change of the Sun in the sky throughout the day. The mechanism behind time-compensated Sun compass orientation has remained obscure. Merlin et al. (p. 1700 ; see the Perspective by Kyriacou ) now provide comprehensive data showing that the mechanism resides in the antennae of the butterflies, rather than the brain, as previously thought. The “antennal clocks” found in the monarchs probably provide the primary timing mechanism for Sun compass orientation. These findings reveal a further function for the antennae—a function that may extend widely to other insects that use this orientation mechanism.