What is it about?

In this study, we investigate a striking collective behavior in tiny worms (C. elegans) in which animals gather into dense groups and continue feeding together, even when dispersing would allow them to access nearby food and avoid starvation. This unusual aggregation does not arise from commonly known environmental cues such as pheromones or oxygen deprivation. Instead, it results from changes in the balance of chemical signals within the nervous system. We found that disruption of a conserved gene, casy-1, alters the balance between serotonin and neuropeptide (PDF-1) signaling pathways. Increased serotonin activity, combined with reduced opposing neuropeptide signaling, shifts worms into a persistent group-feeding state. At the level of individual animals, this imbalance reduces locomotion, impairs their ability to sense neighboring worms through touch, and increases local crowding. Together, these changes scale up from altered neural signaling in single worms to the emergence of coordinated swarm-like behavior.

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Why is it important?

This study shows how group behavior is regulated by neuromodulatory balance. Neuromodulators such as serotonin influence mood, motivation, and social interaction. When this balance is disrupted, behavior changes. Understanding how it is maintained at the molecular level is therefore essential. The study also highlights the role of conserved synaptic genes in shaping collective behavior. Identifying how these genes regulate neuromodulatory signaling provides insight into the fundamental principles governing complex interactions. By linking genes, neural signaling, and behavior, this work offers a framework for understanding how genetic variation may contribute to social behavior deficits. Overall, the study advances our understanding of the genetic and molecular basis of complex group behaviors and provides mechanistic insight relevant across species.

Perspectives

I hope this article makes readers pause and appreciate that complex social behaviours can emerge from alterations in the function of specific genes. Although this study is in a tiny nematode, the broader idea is deeply human. Many of our own collective behaviors, from crowd dynamics to social conformity, are shaped by internal states we rarely recognize. Neuromodulators like serotonin influence mood, motivation, and decision-making across species. Understanding how internal signaling can override seemingly rational choices may help us think differently about social behavior, mental health, and even group decision-making. I also hope this work encourages people to trust their observations, even when they appear puzzling or counterintuitive at first. Watching worms remain aggregated at the edge of abundant food, even at the cost of delayed development, was intriguing. The most rewarding part was not just uncovering the mechanism, but choosing to pursue the question despite setbacks and slowly building a coherent story from it.

Navneet Shahi
Indian Institute of Science

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This page is a summary of: Neuromodulation of swarming behavior in Caenorhabditis elegans : Insights into the conserved role of calsyntenins, Proceedings of the National Academy of Sciences, February 2026, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2520029123.
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