Focusing on Fruit Flies, Curiosity Takes Flight
By JAMES GORMAN
SEATTLE — To hear Michael Dickinson tell it, there is nothing in the world quite as wonderful as a fruit fly.
And it’s not because the fly is one of the most important laboratory animals in the history of biology, often used as a simple model for human genetics or neuroscience.
“I don’t think they’re a simple model of anything,” he says. “If flies are a great model, they’re a great model for flies.
“These animals, you know, they’re not like us,” he says, warming to his subject. “We don’t fly. We don’t have a compound eye. I don’t think we process sensory information the same way. The muscles that they use are just incredibly much more sophisticated and interesting than the muscles we use.
“They can taste with their wings,” he adds, as his enthusiasm builds. “No one knows any reason why they have taste cells on their wing. Their bodies are just covered with sensors. This is one of the most studied organisms in the history of science, and we’re still fundamentally ignorant about many features of its basic biology. It’s like having an alien in your lab.
“And,” he says, pausing, seeming puzzled that the world has not joined him in open-mouthed wonder for his favorite creature, “they can fly!”
If he had to define his specialty, Dr. Dickinson, 50, who counts a MacArthur “genius” award among his honors, would call himself a neuroethologist. As such, he studies the basis of behavior in the brain at the University of Washington, in Seattle.
In practice he is a polymath of sorts who has targeted the fruit fly, Drosophila melanogaster, and its flying behavior for studies that involve physics, mathematics, neurobiology, computer vision, muscle physiology and other disciplines.
“He’s a highly original scientist,” said Alexander Borst, a department director at the Max Planck Institute of Neurobiology in Germany, who has known Dr. Dickinson for years. Usually neuroscientists work either on the behavior or the physics of flight, but Dr. Dickinson, he said, “is interested in both ends.” And, Dr. Borst added, “he’s a wonderful cook.”
Gwyneth Card, who was a researcher in Dr. Dickinson’s lab at the California Institute of Technology, said, “One of Michael’s many talents is he does have the skills to go across these different systems.” Dr. Card, who is now at Janelia Farm, the Howard Hughes Medical Institute research campus in Virginia, is one of the many neuroscientists whose pedigree includes a stint in Dr. Dickinson’s lab. As Dr. Borst puts it, “Many people in the field are his offspring.”
Early on Dr. Dickinson and a mentor solved a longstanding physics problem of insect flight, and he has continued to investigate every aspect of fly flight, sending a steady stream of graduate students and postdoctoral researchers to universities and research institutions where the fly work continues.
His influence on new research extends from basic neuroscience to robotics, and some of his work has been funded by the Defense Department, because flies do an awful lot of complex behavior without a big brain. And, of course, they fly. Researchers at Harvard who built a fly-sized flying robot earlier this year, for example, built partly on his work.
Drawn to Flies
Michael Dickinson grew up in Baltimore. His family later moved near Philadelphia, where he was, as he puts it, “a faculty brat” at an all-boys prep school where his mother taught. As with many teenagers, adolescence was not the happiest time of his life, so he left high school after his junior year.
He did not take his guitar and head for Greenwich Village, however. He went to Brown University, which he started a year early, with a plan to pursue a career as an artist. But he said, “It was pretty clear that was a disaster after the first semester.”
He turned to science. He had taken a course in neuroscience, and began to do research with Charles Lent, on the neurobiology of the feeding behavior of leeches. Along the way, he honed his culinary skills during summers at French restaurants in Cape May, N.J., and Providence, R.I.
Then, in graduate school at the University of Washington, he discovered flies. His research for his dissertation was on fly development and neurobiology, but, he said, “I was almost instantly much more interested in the function of the whole fly than the more mechanistic but probably more well-posed problems of how the little axons grow to the brain.”
After one postdoctoral position that was a misfire, he began working with Karl Georg Götz at the University of Tübingen on insect flight. “We built this very, very simple model of a wing flapping back and forth in 200 liters of sugar water,” Dr. Dickinson said. What they found was that when the wings flap, “they generate this flow structure called a leading-edge vortex.”
By using slow movements of large wings in a viscous medium, they were able to mathematically analyze the fast movements of tiny wings in air. “The technique is called dynamic scaling,” Dr. Dickinson said, and it is often used in aeronautics.
At the time, the nature of insect flight was still quite a puzzle, the basis of the popular myth that engineers had proved that bumblebees could not fly. “We were able to measure the forces,” he said, and to “make simple calculations that, you know, actually insects can fly.”
He was hooked, not only on flies, but on the idea of bringing a variety of disciplines to bear on one complex behavior.
“Fly flight is just a great phenomenon to study,” he said. “It has everything — from the most sophisticated sensory biology; really, really interesting physics; really interesting muscle physiology; really interesting neural computations. Just the entire process that keeps a fly hovering in space or flying through the air — it links to ecology, it links to energetics.”
So when Dr. Dickinson left Tübingen to move to his first full-fledged faculty position, at the University of Chicago, he said, “I tried from that day on to set up a lab that worked in this very integrative way.”
His graduate students and postdoctoral researchers in that lab, and later in his labs at the University of California, Berkeley, at Caltech and now at the University of Washington, have come from a variety of backgrounds, including engineering, physics and biology.
Dr. Card, at Janelia Farm, said the multidisciplinary Dickinson lab at Caltech was a rich environment for a graduate student. “It was a great space to be in,” she said, and Dr. Dickinson was a savvy guide to productive research.
“He’ll set you a great problem,” she said. “For me he kind of picked out takeoff in flies.” She set up a system for taking infrared video at 7,000 frames per second of flies taking off spontaneously and also when they were frightened by an image of an apparent predator.
What she found, and reported with colleagues in a paper in Current Biology in 2008, was that when a predator loomed, the takeoff was not just a reflex action. The flies made preliminary leg movements to prepare for takeoff away from the predator, so somewhere in the fly’s brain the best response to a threat was being computed and a decision being made.
At Janelia Farm, Dr. Card is continuing the work on fly takeoff, using a variety of methods, like turning different brain circuits on and off, to attempt to understand just how the fly brain makes the decision — what exactly happens in what neurons in the milliseconds between the sight of a predator and takeoff.
Fly Fantasyland
Dr. Dickinson’s lab at the University of Washington is a bit like a mini-Disney World for engineers, particularly since most of the researchers build their own apparatuses. The lab takes advantage of all available technologies, including high-speed video, which Dr. Dickinson says does for time what the electron microscope did for space, and optogenetic stimulation of neurons in fly brains.
There are micro-treadmills for the flies and, in a basement room, macro tanks of viscous fluid for robotic wings. There are tiny enclosures for some experiments and tents for longer flights. For years his lab has worked with flies that are tethered and engaged in a kind of virtual reality theater, where the flies react to video of stimuli, like vertical lines, which they use as targets during flight. Sometimes the flies can control the display, as in a video game.
Gaby Maimon, now at Rockefeller University, worked with Dr. Dickinson at Caltech to develop a way to measure the activity of individual neurons in the fly brain during one of these experiments. Even more recently the lab has moved on to capturing images of the brain in action.
That action is very different during simulated flight from when the brain is at rest, Dr. Dickinson said. In fact, a point he emphasizes is that neuron for neuron, the fly brain has a wider range of behavior than more complex mammalian brains. One reason seems to be that the presence of different chemicals called neuromodulators in the fly brain can change how a given group of neurons acts at different times.
Another recent advance in his lab was in the area of machine vision. Kristin Branson, who is also now at Janelia Farm, developed software to analyze video of many flies together to try to understand the behavioral rules that govern their interactions. It is an extremely difficult problem for computers to cope with, given the huge amount of information in all the interactions of flies even over a period of a few minutes.
Dr. Dickinson’s latest research interest will, however, take him out of the lab. He is interested in fly behavior in the wild.
“The genus Drosophila is one of the great success stories,” he said. “There’s hundreds of species within the genus. They’re on every continent except Antarctica, they’re in tropical rain forests, they’re in deserts, they’ve evolved many exotic mating behaviors, and they’re capable of incredibly long-distance flights. They can fly for over 10 kilometers without eating anything.
“One of our more recent observations is that drosophila can read the sky compass,” he continued, “so they have the same capability that monarch butterflies have of being able to basically look at the sky” and figure out direction based on the polarization of light.
With this ability, there’s no need to see the whole sky or star patterns. “It works even when you have only a tiny patch of blue sky. It’s a solution vertebrates didn’t come upon, humans didn’t come upon, but insects did.”
And yet, he says, the world of the laboratory elicits only a limited range of behavior from flies. He wants to see more.
“Most biologists study them in this incredibly benign environment,” he said. But studying something as marvelous as a fruit fly in the lab is “like having a BMW and driving it around the block.”
Except, of course, BMWs can’t fly.
Do Most Flowers Have 5 Petals?
By C. CLAIBORNE RAY
Q. Most flowers I see have five petals. Is this generally true, and if so, why?
A. Many showy cultivated plants do indeed have four or five petals, said Melanie Sifton, vice president of horticulture at Brooklyn Botanic Garden, but another big plant category, the monocots, often have three petals or multiples of three. Even then, the numbers and arrangements vary widely. For example, grasses, palms and orchids are all monocots, but they can have great diversity in petal structure and flower shape.
“Essentially, this is all about sex,” Ms. Sifton said. Most petals are modified leaves that surround a plant’s sexual parts and have evolved in many permutations of color and arrangement to encourage pollination, attract pollinators or both.
For instance, plants with large white petals, like the moonflower Ipomoea alba, are well adapted to attract moths for pollination, Ms. Sifton said. Some flowers have fused petals that look more like funnels or bells, and other flowers have asymmetrically enlarged petals, like orchids. Such arrangements not only attract pollinators visually, they can also act as traps, food mimics and landing pads for pollinators.
Other plants, like those in the aster family, might look as if they have hundreds of petals in a circle around a central core, but actually have many small flowers densely arranged around a central disk of even more flowers.
“To complicate this matter further, there are other flower parts that might look like petals, but are more accurately identified as sepals or tepals,” Ms. Sifton said.
No comments:
Post a Comment