The Butterfly Clock: Illuminating the Molecular Mysteries of Monarch Migration

Each fall, the entire monarch butterfly population of the Eastern United States and Canada funnels into a handful of oyamel pine groves in Michoacan, Mexico, to weather the winter months. Each spring, the butterflies mate and fly north to repopulate the continent in short generational bursts. The monarchs flying south in the fall are three generations removed from those that made the trip the previous year. With no parents to guide its way, a migrating monarch has only its genes to steer it to its Mexican overwintering site. Monarchs orient using the sun as a guidepost. Because the sun appears to move across the sky throughout the day, the butterflies must keep track of time in order to correctly interpret the sun’s position. Although this so-called “time-compensated sun compass” was demonstrated in 1997, little was known about how it worked. Steven Reppert, a neurobiologist at the University of Massachusetts Medical School in Worcester, MA, is working to change that. His lab seeks to understand the cellular and molecular mechanisms monarchs use to guide them on their remarkable yearly journey. Reppert and his colleagues believe they have pinpointed the sun compass, and the circadian clock that guides it, in the monarch brain. They have shown how the clock and compass might work together to allow the monarchs to find their way to Mexico. Their work has also uncovered some unexpected insights into the workings and evolution of circadian clocks in general. This thesis profiles these discoveries, exploring how circadian biology has illuminated monarch migration, and how monarchs, in turn, have illuminated circadian biology.

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