Carpenter ants live in a caste system, where some members of the colony grow into large, strong worker guards known as majors and others grow into small, inquisitive food scouts known as minors. Scientists have long been fascinated by how majors and minors come to be. Though the two castes share the exact same genomes (and parents), they look and behave in dramatically different ways. Clearly, these differences must be epigenetic, or triggered by environmental factors that take hold after the ants are born. Now a group of researchers have shown that just one dose of a specific enzyme, injected into a recently-hatched major's brain, can mess with the ant's epigenome for months.

Many studies have shown that social insects like bees create their biological castes with food. Queen bees, for example, are made by feeding royal jelly to a larva. Speculating that a similar mechanism might be at work in carpenter ants, University of Pennsylvania developmental biologist Daniel Simola and his colleagues attempted to isolate a substance they could feed to ants that might cause one caste to transform into another. Specifically, they wanted to see whether they could induce a major worker to act like a minor worker, abandoning her job as guard to become a forager. They focused specifically on enzymes that affect 160 genes whose activity diverged the most between minors and majors. Those genes included ones associated with learning, memory, and the way neurons communicate with each other in the brain.



Eventually, Simola and his colleagues found just a few enzymes that regulated the behavior of those genes. After several experiments with feeding the substance to their insect subjects, the researchers figured out how to inject the enzymes into the brains of major workers shortly after hatching. The treatment made the ants take on new social roles immediately. Those major workers looked big and powerful like their unmodified major sisters, but they acted like minors, exploring and foraging for food. In a paper published today in Science, Simola and his co-authors explain that they observed the modified majors acting like minors for up to 50 days after hatching. Carpenter ant workers can live up to 7 years, so it's not clear whether this alteration in the insects' behavior would last their whole lives.

The modification ultimately depended on changing the behavior of one particular gene, Rpd3, which set off a cascade effect that changed the behavior of other genes too.

The researchers call this an important step forward in understanding how behavior is "programmed" by non-genetic factors such as enzymes. Their work strongly suggests that complex behavior like scouting for food can actually be altered by drugs. While this experiment was performed entirely with ants, the researchers note that there are similar genetic systems at work in many other species, including mammals.

Write Simola and colleagues in the conclusion to their paper:

Further, our results suggest that [the enzymes] CBP and HDACs might help to establish complex social interactions for other invertebrate, vertebrate, and mammalian species, in which these conserved enzymes are known to play critical roles in the regulation of behavioral plasticity as well as in learning and memory. Finally, our ability to alter a canonical altruistic behavior in a truly social organism by experimental perturbation of a single gene suggests that the application of increasingly versatile reverse genetic approaches in eusocial insects will allow us to expose the general organizational principles underlying complex social systems.

The hope here is that we can at last unlock the chemical mechanisms that help us engage in social activities like sharing work tasks and divvying up jobs. Perhaps these discoveries will even be relevant to mammals like humans.

But do we really want to go down that road? In a slightly disturbing attempt to illustrate how this experiment worked, Science released this educational gif, below. In it, an anthropomorphized major worker holds up a protest sign that says "Will not forage for food." Then a giant needle comes out of the sky and appears to inject stars into her brain. Afterwards, she obediently harvests tomatoes.

Obviously the gif is intended to be lighthearted, but it illustrates a fundamental ethical concern with this kind of work. If we do figure out how to change animal behavior with enzyme cocktails, what is to stop some well-meaning health agency from dosing "problem" people like protesters with it? After all, we'd just be turning those angry protesters into obedient workers. It sounds like a dystopian science fiction future, but the research to make it happen graces the pages of our science journals today.

Science, 2015. DOI: 10.1126/science.aac6633 (About DOIs).