For the first time, scientists have directly linked social cues to an immediate genetic response in the brain, according to a new study in
"People forget that social influences are pretty important," said study co-author Russell Fernald at Stanford University in California. "Here's the case where the social is everything. [It] regulates brain structure in a very direct way."
Characterized by a dynamic social hierarchy, the cichlid fish
Previous work has shown that one week after males become dominant, neurons in the preoptic region of the brain become eight times larger and produce a great deal of gonadotropic-releasing hormone-1 (GnRH1), which regulates reproductive physiology in all vertebrates. To investigate what neural mechanisms rapidly connect social change to this physiological change, the researchers gave subordinate fish an opportunity to ascend in a familiar environment. Molecular analyses focused on
During the experiment, the researchers removed the dominant male from each observation tank containing four females and one other male, then turned on the lights an hour later so that the fish could see the dominant male was missing. Minutes later, the subordinate male changed body color and became more aggressive, with larger testes and other signs of heightened fertility following soon after. Burmeister said she was surprised to see the animals respond so quickly to a change in social environment.
Twenty minutes after they turned on the lights, the researchers used
The work "speaks to how dynamic these [social] situations can be and how natural selection has probably selected for these very, very rapid responses," said Sigal Balshine at McMaster University in Ontario, who did not participate in the study. Because of its "amazing reversibility and capacity for dynamic change," she said,
In a previous experimental model, the researchers moved the subordinate male into a tank where he could become dominant. In this scenario, it took longer for him to respond to the change in environment, something Fernald suspected might be due to the disruptive nature of the experiment. This new system minimized these stresses. "It's as if you woke up one morning in your house, and the neighborhood bully had suddenly moved away," Fernald explained.
In the future, Fernald said, genetic researchers "can now use
According to Burmeister, "the mechanisms that we're looking at are very fundamental" and could be extrapolated to other animals, particularly since both