By studying monarchs inside a specially designed flight simulator, the researchers have gathered what they believe is the first direct evidence of the essential role of the circadian clock in celestial navigation. The study appears in the journal Science, published by the American Association for the Advancement of Science (AAAS).

In the fall, monarch butterflies journey from central and eastern North America to a small region in central Mexico. Only every fourth or fifth generation makes the trip, indicating that the urge to migrate is instinctive, rather than learned.

"Monarchs have a genetic program to undergo this marvelous long term flight in the fall. They are essentially hell-bent on making it to their over-wintering grounds," said Science author Steven Reppert of the University of Massachusetts Medical School.

While scientists are fairly certain that monarchs use the sun to navigate, they know less about how the butterflies adjust their direction each day, as the sun's position in the sky changes. It has long been suspected that monarchs use their internal, "circadian" clock as part of their sun compass.

"We have shown the requirement of the circadian clock for monarch butterfly migration," said Reppert. "When the clock is disrupted, monarchs are unable to orient toward Mexico. Without proper navigation, their migration to the south wouldn't occur, and that generation of butterflies would not survive."

Reppert chose monarchs for the study in part because they don't learn their route, as honeybees foraging for nectar do, for example.

"Monarch butterfly navigation seems to involve the interaction between a clock and a compass. This makes monarch navigation a bit simpler than navigation in foraging insects where each new route has to be learned," Rep
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Contact: Lisa Onaga
lonaga@aaas.org
202-326-7088
American Association for the Advancement of Science
22-May-2003