Connection Between Gene Regulatory Networks and Aggression in Honey Bee Colonies

Collective behaviors exist across many different groups of animals: groups of fish swimming in a circular pattern together, large flocks of birds migrating during the night, and groups of bees coordinating their behavior to defend their hive.

These behaviors are commonly seen in social insects in which up to thousands of individuals work together, often in distinct roles. In honey bees, the role the bee plays in the hive changes with age. Younger bees perform duties inside the hive, such as nursing and building wax, while older bees transition into roles outside the hive, either foraging (foraging) or defending the colony (soldiers).

What determines whether older bees become foragers or soldiers is unknown, but a new study published in the journal nature and its evolution It explores the genetic mechanisms underlying collective colony-defense behavior, and how these mechanisms relate to overall colony aggression.

said Ian Traniello, a former graduate student at the University of Illinois Urbana-Champaign and now a research associate at Princeton University and first author on the study.

“If you ask anyone outside the street to guess which ant is a soldier versus forager, they will probably guess it right 100% of the time, because soldiers are huge. Instead, honey bees have a division of labor based on age, where Older bees tend to be foragers or soldiers, both of which are dangerous and deadly roles.”

A genome-wide association study previously conducted on a subspecies of honey bee in Puerto Rico that has evolved to become less aggressive in recent years revealed strong correlations between variation in the sequences of certain genes and the level of overall colony aggression. The researchers called these genes “colony aggression genes.”

In the current study, the researchers compared the expression and regulation of genes in the brains of soldiers and foragers, and across colonies that varied in aggressiveness. The researchers measured the colony’s aggressiveness by counting the number of stings on suede patches placed outside the hives after a disturbance.

They identified the soldiers as the bees that attacked the spots and the foragers as the bees that returned to the hive with pollen. The researchers then used single-cell transcriptomics and gene-regulatory network analysis to compare the brains of foraging bees and soldiers from low- and high-aggressive colonies.

The researchers found that although there are thousands of genes in the brain that differ in their expression between soldiers and foragers, none of them were part of the list of colony aggression genes. However, when they created models of the brain’s gene regulatory networks, which control when and where certain genes are expressed, the researchers found that the structure of these networks differed between soldiers and foragers—and the differences were greatest when soldiers and foragers came from a more aggressive colony.

“What we think is happening is that the regulation of genes involved in group behavior influences the mechanisms that underlie the division of labor,” Traniello explained. “Therefore, colonies can become more or less aggressive by influencing the level of aggressiveness of the individuals within that colony. Essentially, a forager may be more or less likely to transition into a soldier-like state if the environment calls for it.”

The findings highlight the importance of gene regulation to our understanding of the relationship between genes and behavior.

“Although some studies have found potential genetic differences between soldiers and foragers, this study demonstrates that older honey bees may have the potential to assume any role,” said Jane Robinson (GNDP), director of the IGB and author of the paper. “In more aggressive colonies, likely due to increased danger in the environment, older bees may be more willing to become soldiers to help defend the colony.”

Plans for future directions include developing functional tests to explore the role of gene networks identified in the study, and to spatially determine where they are expressed in the brain. Traniello says he’s looking forward to exploring these new questions.

“We have extraordinary techniques for probing genes and behavior on an unprecedented scale, both with single cell and now, spatial transcription,” Traniello said.

“These give us new means of understanding old questions, such as the relationship from individual to group, or the relationship between genotype to phenotype. It’s exciting to be able to take these tools and apply them in natural contexts, and I hope this work inspires others to do the same.”