Animals rely on group behavior to survive, whether its fish swimming together to avoid predators or humans sharing knowledge with each other. But despite the importance of such social interactions, scientists do not have a good understanding of the biological processes that guide collective behavior.

In a new study published in iScience, researchers at Harvard University and the Max Planck Institute of Animal Behavior developed a new way to study how genes influence collective behavior. Using zebrafish as a model, they set out to establish the connection between genetic mutations and behavior.

We are interested in answering a fundamental biological question: why do animals live in groups? said Mark Fishman, Harvard professor of stem cell and regenerative biology. To search for genes that affect collective behavior, we focused on genetic mutations that are associated with psychiatric diseases that have a social behavior component, including autism and schizophrenia.

The team observed that in fish with specific genetic mutations associated with human psychiatric disease, group behavior was altered. The findings pave the way for a new generation of research into neuropsychiatric conditions such as bipolar disorder, autism, and depression.

The researchers tested 90 different genes to see if they affect zebrafish social behavior, using gene editing to mutate one gene at a time. For each genetic mutation, the researchers put the edited fish together in a large tank to see how they interacted with each other.

We used computer vision to track individual fish and analyze their interactions, said Fishman. By documenting how interactions change among the fish whether they get out of each others way, or whether they align with each other we could see how the overall pattern of group behavior changes.

The researchers found several genetic mutations that had a distinctive effect on fish group behavior. Normally, zebrafish spend much of their time in dynamically moving groups, called schools when all moving together in a coordinated fashion, and shoals when in less directed groups. Some mutations affected these groups, for example causing the fish to be scattered throughout the tank, or huddling together in one location.

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Study connects specific genes with defective social behavior - Harvard Gazette