Understanding how the circadian clock assists the sun compass in the relatively simple navigation by monarchs could provide a model for studying navigation by other animals, Reppert said, citing both foragers such as honeybees and desert ants, as well as long distance migrators such as songbirds.
"We would like to know how the circadian clock functions in four dimensions not only how the clock functions to keep time, but also how time regulates spatial information," he said. "Increasing knowledge of the genetic makeup of the monarch circadian clock will help tease apart the entire migratory process, a process that remains one of the great mysteries of biology."
Research in other animals has been turning up a number of genes that make up the circadian clock, as their expression oscillates in a daily cycle. The clock is "entrained" to the daily light cycle via specialized by special light-sensitive cells, called photoreceptors.
The researchers found that a common clock gene, known as per, is also part of the monarch circadian clock. Constant light disrupted the cycling of this gene's expression. It also affected the time of day butterflies emerged from their chrysalises, known to be a marker of circadian time-keeping in other insects.
Reppert and his colleagues then studied the effects of manipulating the daily light and dark cycles on monarchs inside a specially designed flight simulator, with a video camera and computer that record the flight direction.
After being housed under a light/dark cycle in the laboratory that was close to the fall outdoor lighting cycle (light from 7:00 a.m. to 7:00 p.m.) migrant butterflies exposed to outdoor sun oriented to the southwest, toward Mexico. Butterflies housed under an earlier cycle (light from 1:00 a.m. to 1:00 p.m.) flew to the southeast.
When the butterflies were exposed to constant light, they flew directly toward the sun, presumably having lost their s
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Contact: Lisa Onaga
lonaga@aaas.org
202-326-7088
American Association for the Advancement of Science
22-May-2003