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Research Showcase - Michael Greene, Biology

Applying the mechanics of ant colonies to modern engineering and science

Few would envy a day in the life of Professor Michael Greene. In the summer, he rises at 4 a.m., slips on latex gloves and head-to-toe protective clothing, and heads out to a 120-degree swath of parched earth in the Arizona desert to spend the day playing voyeur to a colony of venomous red harvester ants.

During the school year, when he isn't teaching, he scours campus sidewalks for pavement ants and takes them back to his lab where he and his graduate students stage wars between enemy colonies.

The work, to some, may seem tedious. But Greene sees it differently. "What's not fascinating about ants?" asks Greene, an assistant professor of biology and one of the nation's leading ant researchers. With more than 12,000 species among them and more than 150 million years of evolution behind them, "ants are quite successful as an evolutionary group and incredibly abundant."

It's worthwhile, he says, "to try to figure out how ants work." In recent years, ants have been of particular interest to scientists who believe that understanding their "swarm intelligence" could provide clues about other complex self-organizing systems in computer science, artificial intelligence, neurology and transportation planning. And on a more practical level, Greene says, understanding ants could enable us to better manage them without using pesticides.

For eight years, he has focused primarily on the complex communication systems that allow ants to forage for food, build elaborate highways, keep their nests clean, identify enemies and protect their queen. Their success, he notes, depends on how they operate as a team:

"The truth is, if you watch individual ants it's amazing they survive at all…But when you put them all together, the society is very responsive to changes in their environment."

While film depictions show ant colonies that rely on an ant-in-chief shouting orders to subordinates, in reality, ants are nonhierarchical. "The biggest thing that has come out of ant research is the fact that all of those 20,000 or so workers are able to exist without a boss."

Previous researchers have discovered that different ants have different jobs, typically based upon age. A newborn ant will likely have a job closer to the queen, while an adolescent ant may be a maintenance worker, hauling debris out of the nest. Older ants play patrollers, who scout out food and predators. Then come the oldest—the foragers—who are responsible for retrieving that food.

But how do the foragers know the coast is clear? The key lies in their remarkable sense of smell.

In collaboration with Stanford biologist Deborah Gordon, Greene has demonstrated that not only do ants with different jobs have different odors, those odors subtly incite different actions. For instance, once a patroller returns from the nest to foragers waiting to go to work, the patroller's distinct odor (arising from the unique combination of hydrocarbons that coat its body) will signal the forager to head out. If the patroller never returns—perhaps it was blown away in a fierce wind storm or devoured by a hungry lizard—the waiting foragers know to hang tight.

Greene tested the theory at the Southwestern Research Station in the Arizona desert using an ingenious system. He woke at dawn and kidnapped patrollers from nine colonies of red harvester ants before they had a chance to return to the nest. Then he began to drop glass beads coated with various ant scents into the nest. When beads that smelled like other foragers or maintenance workers were dropped in, the foragers did nothing. When beads that smelled like patrollers were dropped in, the foragers took the cue and headed out.

But it wasn't quite so simple. Greene's follow-up research took the idea a step further, showing that if he dropped one scented bead into the nest every ten seconds, a flood of foragers would exit. If he only dropped one every three minutes, fewer ants left the nest.

In essence: the forager ants had to smell the right smell at the right interval in order to go to work; a subtle, but precise cue repeated over and over between individual ants kept the whole complex system in motion.

"Some of the biggest gains we are going to see in science and engineering will come from learning how nonhierarchical, self-organizing systems are organized and regulated," says Greene, whose work has been published in the journals Nature and Behavioral Ecology, and featured on ABC News and in National Geographic magazine. "What we learn from an ant colony could at least help us frame questions about these other systems."

Ant wars on campus

Job title aside, an ant's unique scent or "hydrocarbon profile" can also identify it as friend or foe to sister ants in a colony—a fact that Greene believes could be of great use to farmers trying to control colonies chewing through their crops.

In summer 2007, using a $100,000 grant from the U.S. Department of Agriculture, Greene began working with students to explore which hydrocarbons elicit a recognition response. The ultimate aim: to develop a bait which could alter an ant's chemical mixture. "We are trying to manipulate the expression of hydrocarbons in a way that will interfere with colony communications, increase aggression between sisters and decrease colony growth," says Nate Bannon, a second-year master's candidate who is working with Greene on the project.

Greene and Bannon have been collecting pavement ants from colonies on campus, bringing them back to the lab, measuring their hydrocarbon profiles and staging and photographing "ant wars" in petri dishes.

"As a student you sometimes feel like you put in your two or three years but you don't ever really get to be involved in the actual solution or the major finding. With this I feel like I could actually be involved in something bigger," says Bannon, noting that he was drawn to Greene for his humility and accessibility.

In the end, Greene says, the joy of teaching and of better understanding ants is reward enough.

But if his work someday enables neurologists to better understand how neurons communicate to create memory in the human brain, or helps airlines devise a better system for organizing flights, all those sweltering days in the desert will have really paid off.