University of Illinois entomology and neuroscience professor Gene Robinson, lead author of a review on the subject this week in the journal Science, says that a critical insight came from a study of songbirds led by David Clayton in 1992, which showed that expression of a specific gene increases in the forebrain of a zebra finch or canary just after it hears a new song from a male of the same species.
The gene, egr1, codes for a protein that itself regulates the expression of other genes, the reviewer points out.
Robinson says that the finding made by Clayton's team drew attention to how powerfully social interactions could alter gene expression in the brain.
Reading that study "was a eureka moment for me," Robinson added.
"This just brought it out into the social world, saying that this occurred in animals that have to make a living in the real world and pay attention to a lot of nuanced stimuli. So I think that was really a very important step in our understanding," he said.
For his own research, Robinson used microarrays to study this phenomenon on a larger scale, and found that thousands of genes actually turned on or off in the honeybee brain in response to social stimuli.
In a study published in 2002, Robinson and his colleagues reported that expression of a gene called "for" did in fact increase in the brains of honey bees as they developed into foragers, and manipulating its expression caused bees to forage precociously.
The researchers also found that social factors, in the form of chemical signals called pheromones, induced this "upregulation" of the gene.
Foragers produce a pheromone that signals to the younger bees that there are enough foragers. If the foragers are removed from the hive, some young bees develop into foragers much earlier in life than usual.
While the for gene is said to have changed over evolutionary time to produce two varieties of fruit flies that differed in their behaviour, Robinson says that social information altered expression of the same gene over a much shorter timescale - within the lifespan of a honey bee - also changing its behavior.
"An appreciation of the idea that differences in gene expression can occur over vastly different time scales helps understand some of the complex relationships between genes, brain and behavior," Robinson said.
Taking into account the picture emerging from such studies, the reviewers came to the conclusion that social signals can have a profound effect on when and how genes function.