A group of researchers in Japan recently set out to uncover the evolution of hierarchy inside ant colonies. Why and how did a queen come be crowned?

How does the same set of genes produce two different classes of ants, worker and royalty?

To solve the mystery, scientists at the Okinawa Institute of Science and Technology Graduate University, the University of Helsinki and elsewhere surveyed the differences between workers and queens in 16 different ant species from around the world.

Instead of looking for genetic differences, the scientists searched for gene sets or patterns that were consistent among workers and queens from all 16 species. By sequencing each species' transcriptome, or messenger RNA molecules, the researchers were able to identify 36 sets of similarly expressed genes.

Because ants have evolved so many unique adaptations, their genome is constantly changing. But the evolution of hierarchy has been constant. For that reason, researchers believe common sets of genes, preserved by evolution -- like the 36 sets -- are more likely to hide the source of hierarchy. Researchers found almost all of the sets of genes they identified were associated with queen or worker traits.

The research suggests the differentiation of queen and worker is inspired not by a specific gene, but by the interplay of these gene groups.

"Our findings further highlight the importance of gene expression for the evolution of traits," lead researcher Alexander Mikheyev, an ecologist at OIST, said in a news release. "In particular, one should consider not just the individual genes involved, but what other genes they interact with."

Mikheyev and his colleagues found the same genetic relationships that influence worker-queen disparity also determine the number of queens in a colony, worker sterility and whether or not a species is invasive.

The research was published this week in the journal Genome Biology.