I. Migration Overview
II. A Time-Compensated Sun Compass
Part I: Migration Overview
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Reppert begins by describing the amazing long-distance migration of the Eastern North American Monarch butterfly. Each fall, several hundred million Monarchs fly up to 2500 miles from the eastern United States and southern Canada to a specific over-wintering area in central Mexico. How do the butterflies know when and where to fly? Reppert explains that the migration is directed largely by an innate sun compass.
In Part 2, Reppert focuses on the time-compensated sun compass system that guides the Monarch’s long migration. He describes how the butterfly eye can sense skylight cues used for directionality, including polarized UV light. This information is integrated in the central complex of the brain, which serves as the sun-compass, then is time compensated, and ultimately interacts with the motor system to control flight direction. While circadian clocks in the brain determine the seasonal migration of Monarchs, distinct circadian clocks in the antennae regulate time-compensation of the sun compass. Interestingly, work at the molecular level shows that the Monarch circadian clock mechanism is distinct and utilizes two cryptochrome (CRY) gene homologues; one previously found in Drosophila and one previously found in vertebrates.
For more details of the monarch migration see http://reppertlab.org
Steven Reppert received both his B.S. and M.D. degrees from the University of Nebraska. He did his clinical training in pediatrics at Massachusetts General Hospital and Harvard Medical School and was a post-doctoral fellow at the NIH in the Section on Neuroendocrinology. He then joined the faculty of Harvard Medical School where he resided for 22 years before moving in 2001 to chair the Department of Neurobiology at the University of Massachusetts Medical School.
For the first 23 years of his research career, Reppert’s work primarily focused on cellular and molecular mechanisms of circadian clocks in mammals. Since 2002, his research has shifted to understanding the biological basis of the long-distance migration of the Monarch butterfly with a focus on its navigational abilities and the role of its unique circadian clock. Reppert’s pioneering research has been recognized with numerous awards including an NIH MERIT award, election as a Fellow of the American Association for the Advancement of Science and the G.J. Mendel Honorary Medal for Merit in the Biological Sciences from the Academy of Sciences of the Czech Republic.
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Froy O, Gotter AL, Casselman AL, Reppert SM. Illuminating the circadian clock in monarch butterfly migration. Science 2003; 300, 1303-1305.
Reppert SM, Zhu H, White R. Polarized light helps monarch butterflies navigate. Curr Biol 2004; 14, 155-158.
Zhu H, Sauman I, Yuan Q, Casselman A, Emery-Le M, Emery P, Reppert SM. Cryptochromes define a novel circadian clock mechanism in monarch butterflies that may underlie sun compass navigation. PLoS Biol. 2008; 6, e4.
Merlin C, Gegear RJ, Reppert SM. Antennal circadian clocks coordinate sun compass orientation in migratory monarch butterflies. Science 2009; 325: 1700-1704.
Heinze S, Reppert SM. Sun compass integration of skylight cues in migratory monarch butterflies. Neuron 2011; 69, 345-358.
Guerra PA, Merlin C, Gegear RJ, Reppert SM. Discordant timing between antennae disrupts sun compass orientation in migratory monarch butterflies. Nat Commun 2012; 3:958.
Heinze S, Florman J, Asokaraj S, el Jundi B, Reppert SM. Anatomical basis of sun compass navigation II: The neuronal composition of the central complex of the monarch butterfly. J Comp Neurol 2013; 521:267-298.
Guerra PA, Gegear RJ, Reppert SM. A magnetic compass aids monarch butterfly migration. Nat Commun 2014; 5:4164
Reppert SM, Gegear RJ, Merlin C. Navigational mechanisms of migrating monarch butterflies. Trends Neurosci 2010; 33:399-406.