Mom genes: What makes a bee brain buzz?

Small carpenter bees
Small carpenter bees
Small carpenter bees
Small carpenter bees (genus Ceratina)

The extremely common “small carpenter bee” (genus Ceratina) can be found all over the world.

Sandra Rehan, an assistant professor of biology at York University who has dedicated much of her career to studying the species, describes them as “often overlooked,” and a very abundant and critical wild pollinator.

These solitary, typically not aggressive bees couldn’t hurt you with a sting even if they tried – but maybe that’s just the way their mothers raised them.

Sandra Rehan

As the principal investigator at The Rehan Lab @ York, Rehan is directing research into the origins of social behaviour in bees like the small carpenters. By observing the bees in their natural environment (living inside sticks) as well as studying comparative genomics in the laboratory, Rehan and her team of researchers are discovering the vital role mother bees play in the genetic and social development of their young.

“There are genes for behaviour,” Rehan explained. “When an individual (bee) forages, guards or cares for offspring, we are interested in what is underlying each heavily regulated trait.

“In terms of studying the evolution of social behaviour, this bee is extremely useful,” said Rehan, noting that the species operate in a malleable system with both solitary and group roles, that provides opportunities to observe long-term parental care. “Not everyone is doing the same thing all the time, so we can look at differences due to ecological factors but also at differences in real-time gene expression and what underlies these different traits.”

Much of what can be learned about bee behaviour begins by “experimentally modifying the social environment,” as Rehan described it. “You can look at a normal system and not know how it works,” she said. “You have to start testing each component to see.”

Small carpenter bee
Small carpenter bee

Having established a baseline of how the bees behave and which genes react when they do, the researchers attempt to perturb the social system and observe how it, along with the bee’s brain, changes.

The work is based on seminal research involving mice and rats which showed a connection between mothers licking and grooming their offspring and a low-stress, low-anxiety, “normative and tolerant” brain.

“When you take away mom, licking and grooming, they become very anxious, avoidant and aggressive with each other,” Rehan explained. “Not being cared for fundamentally changes their behaviour.”

Intrigued by these findings, Rehan has been testing the theory with populations of small carpenter bees.

“It turns out, they tell the same story,” Rehan said. “We can use these bees to understand effect of maternal care on offspring behaviour.”

Female small carpenter bee in a stick nest
Female small carpenter bee in a stick nest

In a study titled “The effect of maternal care on gene expression and DNA methylation in a subsocial bee” published in Nature Communications, Rehan and her team found that when mother carpenter bees are removed from their populations, otherwise calm and tolerant bees begin to avoid each other or become aggressive to one another.

This change can be observed easily in the bees’ behaviour when the mother is gone, but in order to see it in gene expression, Rehan and her team need to look at what the bees’ brains look like frozen, literally, in time.

The field aspect of this research involves translocating the bees’ stick habitats for observation, watching individuals interact, and identifying a bee, or bees – in this case, the mother – to remove from the group.

A subject is put in a small container, the kind takeout dipping sauce comes in, where it can be paint marked, measured, examined for wear and then either kept in observation nests for further study or frozen so its brain can be extracted.

Bee brain layer map
Bee brain layer map

Once a bee brain is frozen and removed, Rehan and her team are able to examine thousands of genes regulated under different conditions to determine which genes and regulatory networks are associated with certain social behaviours and their related social environment.

This is how they can see that the presence of a mother has a significant impact on the makeup of a small carpenter bee’s behaviour.

The researchers’ conclusions aren’t just limited to small groups of the species; they also found that the same gene regulatory networks underly both simple and complex societies, suggesting that this kind of “hard wiring” is in place well before the elaboration of queen and workers castes – a foundational finding for this field.

For Rehan, this demonstrates that the presence of a mother and maternal care for an otherwise solitary being is fundamental to accepting a society and wanting to be with kin. She believes that as species develop their social structures, maternal care may be a critical first step.

genus Ceratina
genus Ceratina

“That could be the golden ticket to understanding how societies evolved,” she said.

Rehan, who joined York in 2019, hopes to continue studying bees from novel perspectives, such as exploring how they are interacting with increasingly urban ecologies, and believes the interdisciplinary nature of her lab positions her researchers to answer complex questions with a collaborative approach.

She noted that, likely due to general concern that bees aren’t doing well, everyday people seem much more interested in bees than they were a decade ago. “They think they are cute, they are important, they want to learn about them,” she said.

While many academics and enthusiasts typically focus their interests on non-native honeybees and pollination systems, Rehan’s lab is unique in specifically studying native species including the small carpenter bees from this perspective.

“There is so much untapped potential,” Rehan said. “It is a unique niche that students come to me to work on. There are so many open questions.”

By Aaron Manton, communications officer, YFile