Fruit Flies' Aerial Stunts Inspire Brain Study

John Roach
for National Geographic News
November 20, 2006
Budding engineers often take apart common devices, such as toasters, and put them back together again to learn how the parts make up a working system.

But budding biologists have a harder time using this approach—once a living organism is taken apart it usually can't be made to function again.

Now, using modern genetic engineering techniques, researchers are able to turn biological components on and off, in effect removing parts to see how each one affects the whole system.

"The more things you take apart, the more intuition you gain about the natural world," said Michael Dickinson, a professor of bioengineering and biology at the California Institute of Technology in Pasadena.

Dickinson studies fruit flies and how certain cells in their brains contribute to their ability to make rapid mid-air turns.

The work, he says, has broader implications for understanding the complexities of the natural world.

"In the end, you learn more than just how flies work," he said. "In figuring out how something as complex as a fly is put together, you gain insight into many complicated processes."

(Read a related National Geographic magazine feature on limb evolution.)

Turn on a Dime

The fruit fly is among the most studied organisms in the world, because its genes can be easily examined and manipulated to simulate human genetics.

With so much knowledge available on individual aspects of the fruit fly, scientists can now embark on answering more complex questions, Dickinson says.

The biologist has recently focused on the interacting mechanisms that permit the flies to make split-second 90-degree turns called saccades.

"All the sophisticated behavior that you see really boils down to changes in the pattern of a handful of cells," he said today in a broadcast of the Pulse of the Planet radio program.

(National Geographic News and Pulse of the Planet receive funding from the National Science Foundation.)

Dickinson explained that flies have image-forming eyes that process information ten times faster than human eyes and sensors that tell the flies how fast they are rotating in space.

(Related news: "Fly Eyes Inspire Better Video Cameras, Motion Detection" [September 7, 2006].)

The flies' brains fuse the information from their eyes with the information from their built-in "gyroscopes" and transform it into the output of a small number of cells that control muscles at the base of their wings.

This, he said, allows the insects to perform their "absolutely extraordinary maneuvers."

Last month, Dickinson and colleagues at Caltech and the University of California at Berkeley, received a $4.4 million (U.S.) grant from the National Science Foundation to further investigate how brain activity controls the flies' complex behavior.

The researchers plan to genetically engineer specific cells in the fruit flies' nervous systems that can be turned on and off with pulses of light.

The technique will allow the scientists to study the function of these cells in living animals.

A central goal of the research will be to understand how fly flight is related to activities such as looking for food and shelter, finding a mate, laying eggs, and getting out of harm's way.

"We will begin with the assumption that an animal's own natural behavior is the best context in which to interpret how its nervous system is built," Dickinson explained in a media statement about the grant.

Complex But Not Incomprehensible

Jane Wang is an associate professor of theoretical and applied mechanics at Cornell University in Ithaca, New York, who studies flapping flight.

She said that while the mechanics of insect flight are relatively complex systems, "there's hope of understanding them."

"Some things are so daunting we don't know where to start," she said. "Here it's daunting, but we have some idea of how to figure this out."

In an interview with National Geographic News, Dickinson says he is primarily interested in flies not only because they are good models for human genetics but also because of what they can say about the mechanics of many biological systems.

"I think it is a valid goal," he said, "to try to figure out how other interesting organisms on the planet work and not focus exclusively on humans."

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