'Selfish DNA' can result in minority influence in social animal groups, including humans

From corporate boards to honeybee hives and ants colonies, groups tend to follow the majority. But biologists and social scientists have found that a vocal minority – sometimes just 5 to 10 percent – can sway the final decision if they’re persuasive, energized, or well-connected. This effect is known as “minority influence.”

A new study shows that fire ants offer a dramatic, gene-driven version of the same principle. A handful of workers carrying a particular stretch of “selfish DNA” can push their nest-mates to welcome extra queens, transforming the colony’s entire social order.

Selfish DNA and ant colony structure

The invasive red imported fire ant, Solenopsis invicta, dominates swaths of the southeastern United States and is spreading on multiple continents.

Ecologically and economically, it is one of the most impactful insects on Earth. It also comes in two distinct social forms.

Single-queen colonies (monogyne) recognize and defend one egg-laying monarch. Workers in these nests are intensely territorial, killing any foreign queen that dares enter.

Multiple-queen colonies (polygyne) tolerate several unrelated queens and spread by budding – new queens and escorts walk a short distance and start satellite nests.

The social form matters: monogyne nests are aggressive but slower to spread; polygyne nests can carpet landscapes with interconnected supercolonies.

A single gene complex, dubbed Gp-9, largely decides whether a colony embraces one queen or many. The variant known as Gp-9 B promotes single-queen structure; the variant Gp-9 b pushes toward multiple queens.

Only workers with the b allele accept extra royalty – and that gene acts in strikingly “selfish” fashion, ensuring its own propagation.

Genetic roots of ant behavior

Takao Sasaki, now an associate professor in the University of Rochester’s Department of Brain and Cognitive Sciences, teamed with postdoctoral researcher Haolin Zeng and Professor Kenneth Ross at the University of Georgia. Together, they tested how small a minority of b-bearing workers could tip an entire colony.

Most previous work had examined stable nests already committed to one form or the other. The new experiments created mixed groups from scratch, mirroring the early stages of an invasion when different ant lineages collide.

“Our research may help us understand how other animals make consensus decisions,” Sasaki said.

Using DNA markers, the team first verified each ant’s social-genotype – B B for single-queen preference or B b for multiple-queen preference. They then built experimental colonies of 3,000 workers and a single B-type queen.

Into these colonies they introduced B b workers in varying proportions, from zero to 30 percent, along with test queens carrying either genotype. Continuous video monitored how workers treated potential newcomers.

DNA can shift the ant colony

With no B b workers present, resident ants killed any stranger queen in the colony within hours, matching monogyne behavior in the wild. But once the minority of B b workers reached roughly 10 percent, the colony’s stance softened.

Those few workers began grooming and feeding extra queens that carried the same b allele, escorting them safely into the brood chambers.

Over the following days, B B workers joined the caretaking – even though the shift ultimately lowers their own inclusive fitness. The single-queen colony had morphed into a multi-queen society, simply because a genetic minority rewrote the ground rules.

“By looking at their genes, we know their preferences for having one queen versus multiple queens,” Sasaki said. “By manipulating the proportion of workers with certain genes, we can test if and how a minority can convince the rest of the group members.”

Chemical communication is the likely mechanism. Fire ants rely on pheromones to tell friend from foe and to decide which queens belong.

Additional tests showed b-bearing workers alter queen pheromones or change how nest-mates respond to those chemical signals. Whichever the pathway, the outcome favors any queen – and thus any gene – matching the minority’s genotype.

Selfish DNA shapes behavior

The study highlights an evolutionary twist known as an indirect genetic effect: one individual’s traits are molded not just by its own DNA and environment, but by the genes carried by its social partners.

Here, the selfish DNA in roughly a tenth of the ants drives an outcome (polygyne structure) that benefits copies of that same element, even though it may not help the colony at large.

“This knowledge is important not only for understanding the biology of social insects like fire ants but also for broader insights into the evolution of cooperation and sociality in animals, including humans,” Zeng said.

Because multi-queen colonies bud readily and thus expand invasion fronts, the ability of a genetic minority to flip nest behavior could accelerate the spread of fire ants worldwide. Evolutionary models will need to account for such feedback between genes and group dynamics.

Ants think like neurons

Sasaki frames the findings in terms of “collective cognition,” his broader research focus. Just as neurons exchange signals to create unified thoughts, social insects exchange chemical and tactile cues to make group decisions.

If a small cluster of neurons can trigger a mental state, why not a small cluster of genetically distinct ants triggering a social state?

“The brain is a good example,” Sasaki explained. “Each neuron talks to other neurons. A brain is a cognitive unit. Ants as colonies make collective decisions like brains do.”

Genes help outvote majority rule

The fire-ant case suggests that minority influence may have a deeper biological foundation than previously realized. In some cases, it’s encoded in selfish stretches of DNA that manipulate social systems like ant colonies from within.

Whether similar elements lurk in other species, subtly guiding flock movements, pack hierarchies, or even aspects of human social networks, remains an open question.

What is clear is that in complex societies, majority rule is never absolute: under the right genetic and social conditions, the few can still lead the many.

The study is published in the journal Proceedings of the National Academy of Sciences.

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