Gene-modified ants shed light on animal societies

Scientists have identified the molecular & neural cues that spur ants to act like nurses and queens. The research can help get a fundamental understanding of how a complex biological system works, reports Natalie Angier.

Whether personally or professionally, Daniel Kronauer of Rockefeller University, USA is the sort of biologist who leaves no stone unturned.  Currently, Daniel 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. The scientists have manipulated the DNA of these ants, creating what Daniel says are the world’s first transgenic ants.

Among the surprising results is a line of Greta Garbo (a Swedish-born American
actress) types that defy the standard ant preference for hypersociality and instead just want to be left alone. 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. Daniel’s lab’s ambitions are lofty and pragmatic. “Our ultimate goal is to have a fundamental understanding of how a complex biological system works,” he said. Daniel and his co-authors describe their work in a series of recent reports that appear in Proceedings of the National Academy of Sciences, The Journal of Experimental Biology and others.

The researchers hope to turn the clonal raider ant into a model organism, right up there with laboratory stalwarts such as E. coli and Drosophila. But while bacteria and fruit flies have proved invaluable for addressing fundamental questions like how genes operate, Daniel’s model ants offer scientists the chance to explore, under controlled conditions, the origin and evolution of animal societies.

Useful applications
One key to the raider ant’s potential as a laboratory workhorse is its adaptability. Many ants are finicky. Not so Cerapachys. “It’s a weedy species,” Daniel said. “That’s true of a lot of model organisms — they have a global distribution, they’re good at invading disturbed habitats, and they’re good at being raised in a lab.”

To trace the knotted skeins of antly social life, the researchers take a battery of approaches. They knock out ant genes or edit the lettering of ant genes and see how the ants respond. They ply ants with radioactively labeled neurochemicals and check where in the ants’ brains the signaling molecules gain purchase. They measure ant movements by fractions of a millimetre as the insects perambulate along finely calibrated grids traced in ceramic.

The project represents basic research at its most seductively cerebral, yet it may well reveal insights into human disease, like why cancer cells ignore all stop signals from their surroundings, or why the brain turns in on itself during depression. “By studying the neuromodulators that make ants so sensitive to their social environment,” Daniel said, “we could learn something fundamental about autism and
depression along the way.”

Mixed signals
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, a single large queen lays all the eggs, and a sprinkling of male ants, or drones, supply the sperm.

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. Moreover, there are no male raider ants: The eggs develop parthenogenetically, without sperm, creating phalanxes of genetically identical female clones.

The ants’ unusual mix of genetic uniformity and wildly protean conduct
offers a powerful tool for cracking the old nature-versus-nurture conundrum.  Daniel’s researchers have been mapping out the interplay between genes and
environmental cues in shaping essential behaviours like reproduction and sociality. Reporting in the journal Current Biology, Daniel and his colleagues described the strictness with which a colony of clonal ants synchronised 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 occasions, 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.

Why is it important to kill off an ant that might breed offseason? Daniel compared the police ants to the body’s immune system, and the rebel ant to cancer. When the ant police come knocking, there’s no rock big enough to hide you.