For the first time, researchers working on migratory Monarch butterflies have identified a molecular pathway possibly linking the creature's central circadian clock to photoreceptors involved in its "sun compass"—which the butterfly uses to orient its flight during migration. Their findings are published in this week's issue of Neuron.

"We've known for a while that the circadian clock plays a role in the Monarch butterflies' time-compensated navigational system, but the molecular mechanisms are still a mystery," said coauthor Steven Reppert, from the University of Massachusetts Medical School in Worchester.

To maintain the constant direction of their navigation during their fall journey south from the northern United States and Canada to Mexico, Monarch butterflies are known to use guideposts of the daylight sky. The most consistent of these references is the sun, but other celestial cues also come into play, such as polarized light reflecting from the sun. Another indispensable...

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