Gene-Modified Ants Shed Light on How Societies Are Organized

Natalie Angier in The New York Times:

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.

…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 though 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 pheromones 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 behavior 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, Dr. Kronauer said, “are the first ones out the door.” Some ants, by contrast, ignore the community cues altogether, and they pay dearly for their scoffery. Reporting in the journal Current Biology, Dr. 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 shut down their ovaries and instead attend to the hungry young. On occasion, though, an ant’s ovaries remain animated when they should be suspended, and other ants can detect the illicit activity through telltale hydrocarbon signatures on the offender’s cuticle. Policing ants soon move in on the hyperovarian individual, drag it out of the nest, hold it down and pull it apart, an execution that can take hours or days. “These ants are like little tanks,” Dr. Kronauer said. Why is it important to kill off an ant that might breed off-season when that ant is your genetic twin? Dr. Kronauer compared the police ants to the body’s immune system, and the rebel ant to cancer. “An ant colony faces similar problems as a multicellular organism,” he said. “You can’t have components that don’t respond to regulatory cues and start to replicate out of control.” When the ant police come knocking, there’s no rock big enough to hide you.

More here.