A group of genes may give some fire ants an advantage, increasing their chances of growing larger and potentially becoming queens, according to a new study from the University of Georgia.
The findings, published in Proceedings of the Royal Society B, offer new insight into how genetics influence ant development and how certain genes improve their own chances of being passed to future generations.
Some fire ant colonies have a single egg-laying queen, while others have multiple queens. A special group of genes, called a supergene, helps determine colony organization.
A supergene is a collection of genes inherited together as a package. In fire ants, this particular supergene contains more than 500 genes and is associated with colonies that have multiple queens.
“We call them supergenes because the genes are tightly linked and inherited together, almost like one big gene,” explained Brendan Hunt, an associate professor in UGA’s College of Agricultural and Environmental Sciences entomology department and a co-author of the study.
Hunt and fellow entomologist Haolin “Horace” Zeng wanted to understand if that same supergene influences how individual ants grow.
More than 3 out of every 4 queens has the supergene
In a fire ant colony, most ants are workers that spend their lives gathering food, defending the nest and caring for the young. Unlike workers, queens reproduce, passing their genes to the next generation.
Smaller workers generally care for young ants and maintain the nest, while larger workers are more likely to search for food. Queens are the largest of all.
Scientists already knew that nutrition, environmental conditions and interactions with other ants help determine whether a developing ant becomes a worker or a queen. The UGA researchers wanted to know whether genetics could also tip the scales.
To investigate, the team studied developing fire ants with and without the supergene.
If you want to pass down a gene, you’d better become a queen.
Haolin “Horace” Zeng
They focused on juvenile hormone, a chemical that helps control insect development. Unlike animals that grow larger by growing faster, fire ants can become bigger by spending more time feeding as larvae before reaching adulthood.
The researchers treated developing ants with methoprene, a chemical that mimics juvenile hormone, to see whether supergene carriers responded differently.
Ants exposed to the treatment grew larger, but the results revealed something unexpected.
While both groups of ants responded similarly to the treatment and could reach the same overall size range, ants carrying the supergene were consistently more common among the largest individuals.
“Among the smallest workers, about half carried the supergene. That proportion increased to roughly 65% among the largest workers and 75% to 83% among queens,” Hunt explained.
‘Selfish’ genes help ants cheat their way into becoming queen
Although all the ants could potentially reach the same maximum size, those carrying the supergene were more likely to grow larger. Because body size plays an important role in determining whether an ant becomes a worker or a queen, researchers believe this advantage could increase a supergene carrier’s chances of becoming a reproductive queen.
“To me, it highlights that, through a developmental mechanism involving body size, a genetic element can alter caste outcomes and basically cheat its way into making a queen,” Hunt said.
Scientists sometimes call this kind of advantage a “selfish genetic element.”
“If you want to pass down a gene, you’d better become a queen. You don’t want to become a worker,” Zeng said.
Genes, hormones, environment all play a role in an ant’s future
But the researchers still don’t know exactly how the supergene influences development.
One possibility is that ants carrying the supergene spend more time growing as larvae. Another is that they use nutrients more efficiently in the larval stage. The researchers have also identified a gene that could help explain the difference.
“This project is the first step in a whole new direction of investigating how this supergene affects development and physiology, which hasn’t been studied nearly as much before,” Zeng said.
For Hunt, the discovery opens the door to a more robust line of study examining how genes, hormones and an ant’s environment work together to determine its future.
Understanding that process could reveal more about how large groups of inherited genes shape physical traits throughout the animal kingdom.