This array shows 306 genes in female swordtails turning on (red), turning off (green) or not changing (black). When females were with attractive males, many of their genes turned off (first column, green). The same genes were turned on when females were with other females (second column, red). The third and fourth columns show gene activity when females were swimming with unattractive males or alone, respectively.
Molly Cummings jokingly calls it the “bar effect:” imagine sitting at a local watering hole with a friend who is behaving perfectly normal, and then someone attractive saunters into the room. You watch as your friend morphs into someone you don’t even recognize.
That quick behavioral change could be caused by the fast action of brain genes turning on and off. At least that’s what Cummings and Hans Hofmann (both assistant professors of integrative biology) recently uncovered in their studies of female swordtail fish.
They found that when a female found a male attractive—she liked his long tail and flashy colors—a large number of genes in her brain were turned off, or “down regulated.” The same genes were turned on when females swam with other females.
“The same sets of genes are having to do opposite things depending on the social situation,” says Cummings.
The biologists speculate that the change in gene activity could lead to a release of inhibition in the females, a transition to their being receptive to mating. They also say that the same genes could be involved in orchestrating mating responses across all vertebrates.
Perhaps most surprising is the rapidness of the action of the genes. Females saw something they liked; genes were up and down regulated; and a behavior emerged, all within a 30-minute time period.
“What we have not appreciated until now his how dynamic the genome is,” says Hofmann. “Even in a very short period of time you can have 10 percent of the protein-coding genome change its activity.”
He likens it to what might happen while a student is taking an exam. “Those 30 minutes of the exam could lead to profound changes in gene activity. That’s exactly what we are seeing with the fish. The same neural circuitry that has generated a behavior before has been changed and may generate a different behavior.”
Their research also led to the discovery of new genes never before implicated in mating behavior.
This article also appeared in the Spring 2008 issue of Focus magazine.
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