Flipping a molecular switch can turn warrior ants into foragers

When it comes to career paths, worker ants split into castes: Some tackle defense, others forage for the colony. But these roles aren’t predestined. An ant’s career trajectory is influenced by factors in its environment early on in life. 

Now, a study reveals one way those environmental factors play out. A protein called CoREST acts like a molecular switch in Florida carpenter ants (Camponotus floridanus), researchers report November 12 in Molecular Cell. By toggling it, big workers fated to be soldiers can be reprogrammed to do the job of their smaller, forager sisters.

Brawny warriors, called majors, and foraging, nursery-tending workers, called minors, share nearly identical sets of DNA. So researchers have looked for epigenetic influences, chemical tags on DNA and associated proteins that can manipulate how genes are read, to explain the different behaviors. 

“And that’s what we found,” says Shelley Berger, a molecular biologist at the University of Pennsylvania Perelman School of Medicine. “It’s the first epigenetic mechanism that’s been found in ants to regulate behavior in the brain.”

The new study highlights that even highly specialized social insects retain substantial flexibility and responsiveness to their environment, says Beryl Jones, an evolutionary biologist at Princeton University not involved in the research. “This is likely another important facet of the great success of social insects,” she says.

Berger’s team had previously shown that injection of a chemical, trichostatin A, that helps unwind tightly packaged DNA could reprogram the majors to behave like minors (SN: 12/31/15). But it wasn’t clear what genes trichostatin A was influencing, or how far along in their development the ants could still switch jobs.

In the new study, Berger and her colleagues injected trichostatin A into the brains of worker ants either zero, five or 10 days after the ants emerged as adults from their pupal stage. These injections could reprogram major workers up to five days into their adult stage, but if administered later, the ants’ roles were already cast and it was too late to change them. 

When the team analyzed gene activity during this five-day window of sensitivity the reprogrammed major workers were producing more CoREST protein than those not injected with trichostatin A. CoREST represses enzymes that break down juvenile hormone, a hormone normally elevated in minor workers, but not in majors, the team found. Boosting CoREST made the warriors more like their minor foraging brethren — with less enzyme production and more juvenile hormone.  

CoREST has long been linked to neurological development, but this is the first time it’s been shown to influence behavior. The protein is found in a wide range of animals, including mammals. Given its ubiquity, CoREST may even play a key role in human biology, Berger says.

“Certainly there are going to be differences between humans and ants,” she says. “But what if CoREST is a really important epigenetic regulator of behavior in humans during early life and even early adolescence?”

Berger next wants to investigate epigenetic changes in ants’ individual brain cells, to see if specific cell types are key to the link between CoREST levels and ant behavior. 

Studies like these that unveil the genetic underpinnings of insect societies make for an exciting time to be studying social insects, says Daniel Kronauer, a biologist at the Rockefeller University in New York City not involved with this research. “People have wondered about the mechanisms underlying [ant] caste development and division of labor for so long, and it feels like we’re finally on the verge of understanding them,” he says.