A team of researchers from the University of Toronto has identified a gene in fruit flies that regulates the types of connections between flies within their “social network.”

The researchers studied groups of two distinct strains of Drosophila melanogaster fruit flies and found that one strain showed different types or patterns of connections within their networks than the other strain.

The connectivity-associated gene in the first strain was then isolated. When it was swapped with the other strain, the flies exhibited the connectivity of the first strain.

The researchers named the gene “degrees of Kevin Bacon” (dokb), for the prolific Hollywood star of such films as Footloose and Apollo 13. Bacon’s wide-ranging connections to other actors is the subject of the parlour game called “The Six Degrees of Kevin Bacon,” which plays on the popular idea that any two people on Earth can be linked through six or fewer mutual acquaintances.

“There's been a lot of research around whether social network structure is inherited, but that question has been poorly understood,” says Rebecca Rooke, a post-doctoral fellow in the department of ecology and evolutionary biology in the Faculty of Arts & Science and lead author of the paper, published in Nature Communications. “But what we’ve now done is find the gene and proven there is a genetic component.”

The work was carried out as part of Rooke’s PhD thesis in Professor Joel Levine’s laboratory at U of T Mississauga before he moved to the department of ecology and evolutionary biology, where he is currently chair.

“This gives us a genetic perspective on the structure of a social group,” says Levine. “This is amazing because it says something important about the structure of social interactions in general and about the species-specific structure of social networks.

“It's exciting to be thinking about the relationship between genetics and the group in this way. It may be the first time we’ve been able to do this.”

The researchers measured the type of connection by observing and recording on video groups of a dozen male flies placed in a container. Using software previously developed by Levine and post-doctoral researcher Jon Schneider, the team tracked the distance between flies, their relative orientation and the time they spent in close proximity. Using these criteria as measures of interaction, the researchers calculated the type of connection or “betweenness centrality” of each group.

Rooke, Levine and their colleagues point out that individual organisms with high betweenness centrality within a social network can act as “gatekeepers” who play an important role in facilitating interactions within their group.

Gatekeepers can influence factors like the distribution of food or the spread of disease. They also play a role in maintaining cohesion, enhancing communication and ensuring better overall health of their group.

In humans, betweenness centrality can even affect the spread of behaviours such as smoking, drug use and divorce.

At the same time, the researchers point out that social networks are unbiased and favour neither “good” nor “bad” outcomes. For example, high betweenness centrality in a network of scientists can increase potential collaborators; on the other hand, high betweenness centrality in another group can lead to the spread of a disease like COVID-19.

“You don't get a good or a bad outcome from the structure of a network,” explains Levine. “The structure of a network could carry happiness or a disease.”

Rooke says an important next step will be to identify the overall molecular pathway that the gene and its protein are involved in “to try to understand what the protein is doing and what pathways it’s involved in – the answers to those questions will really give us a lot of insight into how these networks work.”

And while the dokb gene has only been found in flies so far, Rooke, Levine and their colleagues anticipate that similar molecular pathways between genes and social networks will be found in other species.

“For example, there's a subset of cells in the human brain whose function relates to social experience – what in the popular press might be called the ‘social brain,’” says Levine.

“Getting from the fly to the human brain – that's another line of research. But it almost has to be true that the things that we're observing in insects will be found in a more nuanced, more dispersed way in the mammalian brain.”