Many species of animals form social groups and behave collectively: An elephant herd follows its matriarch, flocking birds fly in unison, humans gather at concert events. Even humble fruit flies organize themselves into regularly spaced clusters, researchers have found.
Within those social networks, certain individuals will often stand out as “gatekeepers,” playing an important role for cohesion and communication within that group.
And now, scientists believe there is evidence that how central you are to your social network, a concept they call “high betweenness centrality,” could have a genetic basis. New research published Tuesday in the journal Nature Communications has identified a gene responsible for regulating the structure of social networks in fruit flies.
The study’s authors named the gene in question “degrees of Kevin Bacon,” or dokb, after a game that requires players to link celebrities to actor Bacon in as few steps as possible via the movies they have in common.
Inspired by “six degrees of separation,” the theory that nobody is more than six relationships away from any other person in the world, the game became a viral phenomenon three decades ago.
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Senior author Joel Levine, a professor of biology at the University of Toronto who went to high school with Bacon in Philadelphia, said the actor was a good human example of “high betweenness centrality.”
Aware of Levine’s link with Bacon, study lead author Rebecca Rooke, a postdoctoral fellow of biology at the University of Toronto Mississauga, suggested the gene’s name.
“The degrees of separation is a real-world thing for us,” Levine said.
Having high measures of centrality in a group network can be positive or negative, Levine explained.
“Patterns of sharing and communication can be absolutely wonderful,” he said. “You also have patterns that contribute to the spread of lethal diseases and infectious diseases, but the structure of the group is the same structure. It’s not a good or a bad or a positive or a negative.”
Levine said that the “degrees of Kevin Bacon” gene was specific to fruit flies’ central nervous systems, but he thought similar genetic pathways would exist in other animals, including humans. The study opened up new opportunities for exploring the molecular evolution of social networks and collective behavior in other animals.
The gene behind fruit fly social networks
The researchers investigated a number of gene candidates in fruit flies, a common lab organism used in the study of genetics.
“We found two versions of the dokb gene and one version produces networks with high betweenness centrality and the other version produces networks with low betweenness centrality,” Levine said.
“A network with a high average betweenness centrality indicates there are individuals in the network important for the flow of information from one part of the network to other parts.”
The team used gene-editing techniques to knock out and swap these distinct variants to see what happened among different strains of flies. This exchange influenced the patterns of interaction among a network of flies, with a social group taking on the pattern of the donor variant.
“The difference that we would see is a difference in group cohesion. It’s not a difference that you would see with your naked eye,” Levine said.
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If you observe video footage of fruit flies in a dish in the lab, Levine said they appear to interact with one another, forming repeatable patterns specific to different strains that can be analyzed statistically.
“What we know is that there’s a repeatable structure to the groups that they’re in,” Levine said. “And we imagine that those structures facilitate how they live.”
In nature, fruit flies show group behavior when laying eggs and encountering predators, Levine said.
“In our paper, we don’t actually characterize what is flowing through the network, so it is hard to speculate what advantages/disadvantages there are to flies who form these different patterns of interaction,” he explained in an email.
“However, we do show that the two different dokb variants exist in several wild strains of flies spanning the globe and that one of these variants correlates with low elevation environments,” Levine said. “Perhaps in low elevations, certain patterns of interaction are advantageous? Again, we don’t directly test this, so it is just speculation.”
Allen J. Moore, a distinguished research professor at the University of Georgia’s department of entomology, said in an email that the research was “careful work” and he agreed with the findings.
“Although a first step — and we (and they) don’t know exactly how it works — it is fascinating to find a single gene that influences social cohesion,” said Moore, who wasn’t involved in the research but reviewed the paper before publication.
What fruit flies and humans share in common
Drosophila melanogaster, best known for hovering around fruit bowls, has been a model organism to explore genetics for more than 100 years. The insects breed quickly and are easy to keep.
While flies are very different from humans, the creatures have long been central to biological and genetic discovery.
“Fruit flies are useful because of the power of manipulation. We can investigate things experimentally in Drosophila that we can only examine indirectly in most organisms,” Moore said.
The tiny creatures share nearly 60% of our genes, including those responsible for Alzheimer’s, Parkinson’s, cancer and heart disease. Research involving fruit flies has previously shed light on the mechanisms of inheritance, circadian rhythms and mutation-causing X-rays.