Social position changes the brains of fish

Peter Dijkstra’s research on how social stress affects fish brains has a way of catching the attention of media outlets. Under that layer of headlines, however, is a simple question:

Can anxiety of occupying a lower social status lead to diseases that cause a decline in brain function?

He asked that question when he came to CMU in 2015. Since then, he’s mentored 40 undergraduate and 10 graduate students.

Last year, for example, he co-published a paper that said stress related to social hierarchy might damage the brains of African cichlids. The inquiry has proven popular with media outlets in the U.S. and Europe.

Media outlets in Europe took notice. The attention helps lift CMU’s reputation and highlights science in general.

“The international attention Dijkstra’s work has received highlights the extraordinary work done by the faculty at Central Michigan University and shows the importance of doing science and its worldwide impact,” said Brad Swanson, interim vice president for research and innovation at CMU.

Attention aside, the underlying question has big implications, said Dijkstra, a faculty member in the College of Science and Engineering’s Biology department.

Research has connected the kinds of physical changes he’s seen in the brains of cichlids suffering from social stress to diseases like dementia and Parkinson’s.

Paper looks at the brains of tropical aquarium fish

His latest paper involved the brains of Burton’s Mouthbrooder, a highly social species of cichlid, a tropical fish popular in aquariums. Males are also territorial and establish clear hierarchies. Their territorial behavior is also of interest to biologists and neurologists.

It turns out that fish at the bottom of the social strata know it and feel it, he said. It was enough to change how their brains function through the creation of highly unstable molecules called free radicals.

On the flip side, the adage “heavy is the head that wears the crown” is also true. It turns out, being at the top also causes stress, as the king of the hill faces competitors trying to take what they have, he said.

Stress connected to molecular instability

Free radicals damage DNA and certain proteins by stealing electrons from other. At a large enough scale this theft is linked to aging, cell damage and cancer. The process is called oxidative stress.

It’s not exactly new that individual organisms at the bottom of social strata are stressed over it. They get fewer opportunities to mate, and in fact, the gonads of lower-strata male Burton’s Mouthbrooders are smaller than upper-strata males, his research concluded.

For this research, Dijkstra also focused on something different.

Do fish at the top suffer stress?

“What are the dominant males experiencing,” he said.

They released fish into an aquarium, where they promptly set up a clear social hierarchy. Dominant males occupied the best nesting ground and turned brighter colors. Submissive males got what was left over.

When they examined the brains of both kinds of fish, they found that both had damage from oxidative stress, he said. The interesting thing is that the damage was manifested in different regions of the brain depending on where the fish was in the social hierarchy.

Lower-status fish had oxidative stress damage to the fish’s DNA in the mid-brain region; upper-status fish had oxidative stress damage to the fish’s DNA in the hypothalamus region.

In a press release outlining his findings, Dijkstra said that the study doesn’t draw any major conclusions but raises interesting questions for further research.

“I think we just uncovered some interesting patterns across different divisions of the brain,” Dijkstra said in an article in Frontiers of Neuroscience. “The next step is to understand the regulation of oxidative stress better and how social stress influences this. This requires more rigorous experimental studies.”

Because cichlids are such a territorial, hierarchal fish, they make excellent study subjects to look at social settings, he said.

His current research tracks are being funded by a $443,000 grant from the National Institutes of Health.

In addition, they are easy to maintain and have a certain something.

“They’re very beautiful animals,” he said. “Very charismatic.”

Previously, Dijkstra’s lab made waves after discovering that female Burton’s Mouthbrooders ate their own young as a means to relieve stress and how the proximity of territory relates to oxidative stress damage.

He’s also expanded the basic question to whether the chances of someone winning a judo contest are enhanced by the color of their uniform.