Believe it or not, bullying is not only bad for humans – but fish too!

Hello, Tyrone here! You know what’s not fun? – Being bullied and harassed over long periods of time. I’ve been picked on by dominant males before, especially Burt, and because of it I wanted to better understand the effects of this constant bullying on the behavior, brain, and overall health of a fish like me.

Luckily, the scientists are interested in this too! They study the effects of repeated bullying using something called a resident-intruder paradigm. Males of our species are either dominant (like Burt) or subordinate (like me, Tyrone). Dominant males are brightly colored and aggressively defend their territory from rival males like me. In a resident-intruder paradigm, there is a tank divided into two territories by a solid barrier. One side contains an intruder male, and the other side contains a resident dominant male who is slightly larger than the intruder. If you place the intruder male into the resident male’s territory, he will be socially defeated by that resident. What does social defeat look like, you ask? An intruder male is socially defeated when he stops trying to fight back and starts performing coping behaviors like freezing or swimming away or hiding, while the resident continues to be aggressive. Scientists can use this set up to study just one instance of bullying or repeated bullying over time – called chronic social defeat!

Here’s where it gets interesting. If a male is socially defeated over a long period of time, even after given a break from being bullied, there is a good chance his coping behaviors might change!  If I were trying to get Burt to stop bullying me, I would cope by using a mix of strategies such as being aggressive and attempting to escape or freezing, hiding, and not trying to escape sometimes. What would be really strange is if I did nothing but freeze when in the presence of Burt. But that’s exactly what the scientists saw for some of the chronically defeated males!

So far, it looks like males who are chronically socially defeated can be divided into two different groups: 1) unaffected or resilient (will use a combination of different coping strategies like me!) or 2) reactive or susceptible (exclusively freeze as a coping strategy). As a result of long-term bullying these susceptible males display a behavioral abnormality and may be less successful with the ladies.

Scientists also found differences in the brain of resilient and susceptible males! A brain network called the social decision-making network mediates a lot of social behaviors in many different animals – including stress coping behaviors in response to bullying. Using a neural activation marker called pS6, scientists found differences in specific regions of this brain network between resilient and susceptible males, which is pretty cool!

For example, in a region called the anterior thalamic nucleus (ATn), control males that were not socially defeated had some activation, but not as much as in the socially defeated males! Also, in the superior raphe nucleus (SR), found in the hindbrain, scientists see a lot of activation in non-socially defeated males and almost none in the socially-defeated males.

Overall, scientists are able to show some of the negative behavioral impacts of this repeated social defeat, which can influence how successful males like me might be in the future when we try to challenge males like Burt to take over their territory. This includes better understanding how the brain regulates different coping behaviors in response to bullying, which is something that happens in lots of animals that live in a dominance hierarchy like monkeys, or even humans! One day this knowledge could also be used to better understand human psychiatric disorders such as depression and PTSD!

Check back in the future for more updates on this research project!