(credit: Alex Wild)
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.
In this video, the researchers explain how the ant caste system works.
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.