MY RESEARCH | ADVANCED SEARCH | UNC HOME
The Office of
307 Bynum Hall
Campus Box 4106
UNC-Chapel Hill
Chapel Hill, NC 27599-4106
Tel: (919) 962-6136
This is a fish story. But it’s not about the one that got away—it’s about the ones that stayed behind. When Sabrina Burmeister, now a research assistant professor at Carolina, and her colleagues at Stanford University took dominant male African cichlid fish out of their tank, the remaining subordinate males became dominant within minutes.
Two dominant cichlid males dispute a territorial boundary as a way to demonstrate authority.
Previous experiments have shown that, given the chance, a subordinate cichlid male will eventually become dominant. For example, when researchers take a subordinate male out of his tank and put him in a new tank, the subordinate’s colors will, in time, change from drab to bright. He’ll start sporting a new black stripe called an eye bar, and he’ll generally start behaving like he owns the tank and all the females in it. But those changes have tended to happen over the course of a few days.
So Burmeister decided to see what would happen if she more or less instantly removed the dominant male from the tank. She did it at night, in complete darkness, when the cichlids can’t see well and aren’t very active.
Burmeister wore infrared night-vision goggles and took the dominant male out one hour before turning the room lights back on.
“We used this nighttime, kidnap-the-bully approach as a gentle way of not disturbing other fish in the tank,” Burmeister said.
When the lights came on, it didn’t take long for the subordinate male to realize that the top fish was gone.
Within minutes, the subordinate’s colors started to change. He developed an eye bar and started bullying the rest of the fish.
“Once they start changing, there’s no question that they’ll become dominant within two to 10 minutes,” Burmeister said. “It’s like they decide to go for it. They know their position in the hierarchy, and they make a decision to change.”
Burmeister and colleagues then examined the brain cells of the formerly-subordinate cichlids.
They were looking for a gene called egr-1, which helps turn other genes on and off. Their theory was that the egr-1 in the brains of newly dominant males would signal hormone-producing cells to start growing.
The hormone-producing cells would then quickly help make the subordinate male dominant. Compared to both dominant males and subordinate males, newly dominant males had twice as much egr-1 in their brains.
Study co-author Russell Fernald, of Stanford University, said this research provides the first direct evidence that changes in social status can trigger cellular and molecular changes in the brain.
“I think there could be parallels in human social status change,” he said. “If you’re in a situation that’s socially awkward, it may influence how well you can speak, or your sense of yourself may be altered. Those reactions have to have some kind of cellular underpinnings.”
Burmeister said these fish are always on the make, so to speak. “They must constantly be ready, because they make the shift in no time,” she noted. “They keep track of who’s who and who’s the biggest so they can take the opportunity to reproduce.”
The study appeared in the November issue of PLoS Biology. The study’s third co-author is Erich Jarvis of Duke University. The National Institutes of Health and the National Science Foundation funded this research.
Provided by the Division of Research and Economic Development
Editor: Neil Caudle
Writer: Jason Smith