Among the surprising results is a line of raider ants that defy their standard preference for hyper sociality and instead just want to be left alone.
Daniel Kronauer of Rockefeller University and his colleagues are assaying the biology, brain, genetics and behaviour of a single species of ant in ambitious, uncompromising detail. The researchers have painstakingly hand-decorated thousands of clonal raider ants, Cerapachys biroi, with bright dots of pink, blue, red and lime-green paint, a colour-coded system that allows computers to track the ants’ movements 24 hours a day — and makes them look like walking jelly beans.
The scientists have manipulated the DNA of these ants, creating what Kronauer says are the world’s first transgenic ants. Among the surprising results is a line of Greta Garbo types that defy the standard ant preference for hyper sociality and instead just want to be left alone.
Under controlled environment
The researchers also have identified the molecular and neural cues that spur ants to act like nurses and feed the young, or to act like queens and breed more young, or to serve as brutal police officers.
“Our ultimate goal is to have a fundamental understanding of how a complex biological system works,” Kronauer said. “I use ants as a model to do this.”
As he sees it, ants in a colony are like cells in a multicellular organism, or like neurons in the brain: their fates joined and their labour synchronized.
“But you can manipulate an ant colony in ways you can’t easily do with a brain,” Kronauer said. “It’s very modular, and you can take it apart and put it back together again.”
Kronauer’s model ants offer scientists the chance to explore, under controlled conditions, the origin and evolution of animal societies.
Beyond its amenable weediness, the clonal raider ant seems almost custom-tailored for experimentation. The world’s some 12,000 known species of ants display a variety of reproductive and survival strategies. The most familiar examples are the fully eusocial ants, in which many sterile female workers do all the chores and a single large queen lays all the eggs.
Keys lies in olfactory receptors
Sequencing the genome of the ant, the scientists found that one class of odorant receptor genes had been “massively expanded,” Kronauer said, suggesting that C. birois may be even more dependent than the average ant on chemical communication. The researchers then used gene knockout techniques to eliminate that category of odorant receptors from some ants, and the results were startling.
The knockout ants had no trouble detecting food. In fact, Kronauer said, “they would eat much more than other ants do.” Their appetite for socializing was another matter.
Whereas normal raider ants will happily pile on top of one another whenever possible, the knockout ants avoided the crowd, instead wandering around on their own for days at a time, as if they were nothing more than the average asocial beetle.
The results suggest that the diversification and specialization of olfactory receptors were keys to the evolution of ant sociality.
The researchers are also exploring the biochemistry of caretaking, asking which signals prod ants to leave the nest and find food for their young.
Preliminary results suggest that volatile chemicles exuded by newborn larvae stimulate the brains of adult ants to begin generating the hormone inotocin, the ant’s equivalent of oxytocin, which is famed for its role in promoting nurturing behaviour among mammals. For raider ants, an inotocin surge galvanizes the urge to venture forth and start plundering and ants with the greatest number of inotocin-making neurons, Kronauer said, “are the first ones out the door.”
Kronauer and his colleagues described the strictness with which a colony of clonal ants synchronized its schedule: Now everyone lays eggs, now the eggs hatch into larvae, now the adults stop producing eggs and instead attend to the hungry young.
Among clonal raider ants, there are no permanently designated workers and queens. Instead, all the ants in a colony switch back and forth from one role to the other. About half the time, they behave like workers, gathering food for their young — generally, by raiding the nests of other ants and stealing their larvae. The rest of the time, they go into queen mode and all colony members lay eggs together.