WallStreet Journal
Using Butterfly Time, We Can Learn Secrets Of Our Own 'Clocks'
Friday February 8, 2008 11:40 am ET
By Robert Lee Hotz

In the highlands of central Mexico, millions of monarch butterflies soon will stir from their winter torpor, rising from groves of oyamel firs like flowers taking flight. Their unique annual migration offers scientists a rare insight into the molecular biology of time and travel.

"What good is a butterfly?" said entomologist Lincoln Brower at Virginia's Sweet Briar College. "It can tell you about the fundamental biology of all creatures on this earth. There is something so fundamental about finding your way."

In a majestic seasonal rite, a new generation of monarchs flies to Mexico every fall from summer breeding grounds in Canada. This past year, they formed a billowing wind-borne quilt of 55 million or more.

Now, in the depth of winter, the monarchs can sense spring. By March, they will be returning north. Unlike most migrating birds, fish or mammals, however, none of these individual insects will ever complete their species' entire 4,000-mile annual journey. These northward-bound butterflies will get only as far as the U.S. Gulf Coast, where they will lay eggs and die. Their descendants must finish the trip.

"With the Monarch butterfly, it is a multigenerational round-trip," said research biologist Richard Holland at England's University of Leeds. "It is the grandchildren or great-grandchildren who make it back to where the adults started the year before."

Following the seasonal growth of milkweed, on which they thrive, the new generations of butterflies edge progressively north, breeding every few weeks, until by high summer, monarchs once again reign in Canada.

For these creatures, migration always is a maiden voyage.

In the fall, the cycle of migration will begin anew. Monarchs of the north always return to the same 12 forest groves in Mexico -- sometimes to the same tree -- that their ancestors left months before. "We don't know what brings them back to the same places every year," said Dr. Brower. "When the sun hits the colonies, they light up like a pumpkin. The monarchs spread their wings and the trees turn bright orange."

On its voyage, the monarch is guided by a biochemical pendulum of genes and proteins that keep butterfly time, neurobiologist Steven Reppert at the University of Massachusetts Medical School and his colleagues reported last month in the journal PLoS Biology. Its newly analyzed internal clock likely is unique among all living creatures -- a prototype, perhaps, for the biological clocks that guide our own circadian rhythms of sleepiness and wakefulness, the scientists reported.

The monarch's sense of time is crucial to its survival as it flies by the sun across open country, experiments have shown. Its innate chronometer allows it to compensate for the sun's passage across the sky during the day, enabling feats of transcontinental navigation that, left to human calculation, might require the Global Positioning System and a computer-aided autopilot. Without a reliable clock, a traveler relying solely on a sun compass could easily get turned around, from morning to afternoon.

In its biochemical essence, the monarch butterfly is a distillation of time and light, given wing. "What they have found actually transcends monarchs," said evolutionary biologist Orley Taylor at the University of Kansas. He is director of Monarch Watch, which tags and tracks thousands of them every year.

Weighing barely an ounce each, the butterflies have been clocked at speeds of up to 30 miles per hour, observed as high as 12,000 feet and seen to fly 375 miles over open water. There are at least three major monarch broods in the Americas but only the largest, which lives east of the Rocky Mountains, travels such daunting distances -- farther than any other known insect species.

Seeking the secret of time and the butterfly, Dr. Reppert and his colleagues studied rhythmic molecular changes in the four brain cells that serve as the monarch's timing device. He discovered that two similar light-sensitive genes drive the clockworks. The first, common to plants and insects, is sensitive to blue light and appears to synchronize the cells to cycles of light and darkness.

The second gene "stunned" the scientists, Dr. Reppert said, because it so closely resembled one previously found only in humans and other mammals. It doesn't respond to light directly but, when triggered, makes a rising amount of protein that measures the passage of time since it was last activated.

"It functions in the butterfly clock almost identically to the way it functions in our clock," he said.

To completely decipher the biology of monarch navigation, Dr. Reppert and his collaborators at SymBio Corp. in Menlo Park, Calif., started last summer to sequence the 250 million base pairs of DNA that make up the butterfly's entire genome. "When you do something like this, you may discover a lot of genes," said company CEO Robert Feldman. "It is an iconic insect."

In small things considered is the world revealed.

sciencejournal@wsj.com



Mail to Friend Email Story
Alerts Set News Alert
Printer
Version  Print Story 

WallStreet
·Keeping the Spark Alive
·Like I'm On Stage'
·Airlines Face a Wary Audience


Copyright © 2014 Yahoo! Inc. All rights reserved. Privacy Policy - Terms of Service
© 2014, WallStreet Journal