New paper: Rats show prosocial behavior in a natural setting

Comparing types of behavior between species is never straightforward. Types of social behavior for example, are not always expressed exactly the same. It would for example be rare to see human families or other social groups lick each others teeth to greet each other, such as wolves do. On the other hand, sometimes behaviors might look the same, but they mean something quite different. A smiling dog is really just breathing; it expresses joy in a different way. Often we see common types of behavior in many species, but the ways these behaviors are expressed, developed based on the specific needs of the species (food situation, group organisation, location).

If we consider prosocial behavior (helping behavior, consolation) to be a social behavior intended to reduce stress, we should in our study be looking at patterns of behavior following situations that are stressful to the species we work with. Studies with other group animals looked for signs of consolation behavior after stressful fights in the group. Our seminatural environment proved to be the perfect setup to study those spontaneously occuring fights. 

The goal of this study was not solely to determine if rats show prosocial behavior, but also to study whether antidepressant use during pregnancy would have consequences for the child on this kind of behavior. Just as in previous work, we let healthy female rats breed with healthy males and afterwards separated the females into two treatment groups. During pregnancy and breastfeeding we treated these mothers with either the antidepressant fluoxetine or with a control substance. The offspring was thus either exposed or not exposed to fluoxetine during their development. After the 32 pups had grown up, we put them in our seminatural environment for eight days (eight at a time) and observed their behavior. If a fight occurred, we observed what each rat did in the following 15 minutes. In particular we were interested in social behavior (sniffing, grooming) and if witnessing or not had an influence on the behavior.

The first thing we noticed, was that females in the control group who witnessed the fight spent more time (during more episodes) on grooming other animals compared to the control females who did not see the fight happen. If only the animals who see the stressful situation react with this type of behavior, this reaction must be related to an implicit ‘understanding’ of the situation. Interestingly, females that had been exposed to fluoxetine, showed this consolation-like behavior less than control females, and equally when witnessing and not witnessing. This may not be entirely surprising, since fluoxetine exposure was linked to lower levels of active social behavior in our previous paper.

We further analyzed whether the consoling animal consoled the winner of the fight, the loser, or other rats. Even though it looked as if the consolers had more attention for losers of the fights, this did not turn out to be statistically significant.

Maybe surprisingly, both control and fluoxetine-exposed males did not show more active social behavior, or grooming behavior, after a stressful fight. Can we then conclude that male rats do not have the ability to show consolation or procosial behavior? Not quite. Maybe males do not experience this type of fights as so stressful that consolation is necessary. We know from other studies that male rats are capable of helping behavior, which is a form of prosocial behavior too.

Does this research definitively show that female rats are capable of consoling conspecifics? Not exactly. First of all, quantifying the stress levels caused by stressors is possible by measuring stress hormone. In our current setup, that is not possible without disturbing the animals. This means that we don’t really know if the fights did cause significant stress, or if the stress was relieved by being groomed. Still, our results are the first to argue that rats might have to be added to the growing list of species capable of the complex and socially beneficial behavior that is consolation.

This study is part of a collaboration between our group at UiT The Arctic University of Norway and the University of Groningen. It was funded by Helse Nord RHF.

[Summary by Roy]

Heinla, I., Heijkoop, R., Houwing, D.J., Olivier, J.D., Snoeren, E.M.S. (2020). Third-party prosocial behavior in adult female rats is impaired after perinatal fluoxetine exposure. Physiology and Behavior. doi: 10.1016/j.physbeh.2020.112899