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40 genes aid in monarch migration: activity differs between southbound, homebody butterflies.

Come fall, monarch butterflies feel the need for a change in latitude. A new study shows that changes in the activity of a suite of genes in the butterflies' brains help the insects find their way to over-wintering grounds in Mexico.

Steven Reppert, a neurobiologist from the University of Massachusetts Medical School in Worcester, leads a team of scientists on an ongoing mission to uncover the monarch's migratory signals. The team describes a new genetic analysis of stationary summer monarchs and fall migratory monarchs in the March 31 BMC Biology.

At least 40 genes are involved in keeping the monarchs Mexico-bound once they head out, Reppert and his colleagues report. The team analyzed more than 9,000 of the monarch butterfly's genes, about half of the genes in its genome.

Each fall, hundreds of millions of monarchs in the eastern United States and Canada begin flying south for the winter and forego reproduction. The butterflies navigate with internal clocks and use the sun as a compass to find their way to oyamel fir forests in central Mexico. No one knows what environmental signals flip the switch that causes butterflies to start migrating.


Some of these 40 genes may be involved in the flip, but the new study didn't address that question.

Reppert and his colleagues collected monarch butterflies in the summer and fall. As expected, stationary summer butterflies have high levels of a reproductive chemical called juvenile hormone, while migratory fall butterflies are deficient in the hormone. Summer butterflies stay near the place they hatch and reproduce, and they don't orient themselves according to the sun. The researchers gave some of the fall butterflies a chemical that mimics juvenile hormone and then placed them in a flight simulator to see whether the hormone could block navigation. But the fall butterflies still had accurate compasses, indicating that reproduction and navigation are controlled by separate systems.

Next, the scientists analyzed gene activity in summer and fall butterflies and found 40 genes showing differences. Of those, 14 were more active in fall butterflies and 26 were more active in summer butterflies. Only two of the genes had any obvious, known connection to migration--vrille, which is part of the butterfly's circadian clock, and the gene for tyramine beta hydroxylase, which is involved in motor behavior. The other genes are involved in metabolic processes, brain development and other processes, and the functions of 15 genes are unknown. "Nothing stood out and said, 'I'm a migration gene,'" Reppert says.

Orley "Chip" Taylor, an insect ecologist at the University of Kansas in Lawrence and director of Monarch Watch, says it is disappointing that none of the genes Reppert and his colleagues found is definitively linked to navigation. But he says, "I think they're doing exactly what needs to be done to unravel all of this."

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Title Annotation:Genes & Cells
Author:Saey, Tina Hesman
Publication:Science News
Geographic Code:1USA
Date:Apr 25, 2009
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