Researchers at India's IISc have uncovered how a single gene mutation triggers swarming behavior in worms, revealing deep evolutionary roots in social regulation. Professor Kavita Babu's lab found that disrupting the CASY-1 gene in *C. elegans* worms disrupts serotonin signaling, causing them to swarm collectively even when food is nearby. This self-emergent swarming, observed even in single mutants, mirrors behaviors seen in locusts and suggests conserved neuromodulatory control of social behavior. The study, published in PNAS, used CRISPR to generate mutants lacking CASY-1, a protein related to human calsyntenins, and found it specifically disrupts pigment dispersing factor (PDF) signaling.

This unexpected behavior emerged when PhD student Navneet Shahi noticed mutants dispersing differently from wild types. Collaborating with physicists, the team modeled the movement, discovering the swarming arises spontaneously. They then used optogenetics to precisely control neuron activity, confirming serotonin as the master regulator tuning group interactions. The findings suggest fundamental genetic encoding of social behavior, moving beyond past focus on pheromones or environment.

The research highlights *C. elegans* as a powerful model for studying population-level behaviors due to its well-characterized nervous system. Future work will explore how genetic changes produce different outcomes under varying conditions, aiming to uncover universal rules of collective behavior across species.