A research team from the Department of Physics of the Universitat Politècnica de Catalunya - BarcelonaTech (UPC) has published an innovative study in the journal Proceedings of the National Academy of Sciences (PNAS) revealing how speed influences social interactions and leadership within fish schools. The study, featured on the cover of PNAS, is led by researcher Andreu Puy from the Condensed, Complex and Quantum Matter (CCQM) research group. It demonstrates that fish tend to create temporary leadership patterns based on the relative speeds of individuals: they align with faster neighbours and ignore slower ones.

Using a novel analysis technique called force maps, which analyse variables such as attraction, repulsion and alignment, researchers have identified the alignment forces that shape the collective movement of fish schools. The conclusions obtained using this methodology have been validated with an agent-based model, a type of computational model that allows the simulation of actions and interactions of autonomous individuals in a given environment, determining their effects on the system as a whole.

Selective attention is key
The study provides new insights into the underlying mechanisms of social interactions in animals and a deeper understanding of the emergence of leadership based on the variable and adaptive speeds of individuals. It suggests that the mechanisms of attention switch in collective behaviour are crucial: selective attention would reduce the cognitive load of individuals and facilitate efficient and accurate group decision-making processes.

Thus, if we interpret social interactions between individuals as a method to transfer information across the group, the results of the study suggest higher relevance of information provided by faster-moving individuals. This makes biological sense as individuals acting on privately acquired information, such as perception of a predator or food, are expected to move at higher speeds. Also, faster movement cues, embedded in a background of slower movements, are perceptually more salient. Finally, the lateral line of fish, with which they detect movement, vibration and pressure gradients in the surrounding water, is also reactive to neighbouring individual speeds.

Entitled “Selective social interactions and speed-induced leadership in schooling fish”, the study provides a different perspective on the mechanisms of movement coordination in natural and artificial systems and could have applications in crowd management strategies or in engineering, such as swarm robotics and autonomous cars. The study was conducted by UPC researchers Andreu Puy and Romualdo Pastor-Satorras; Elisabet Gimeno and Jordi Torrents, also affiliated with the Department of Condensed Matter Physics of the University of Barcelona; Maria del Carmen Miguel, from the same UB’s department; and Palina Bartashevich and Pawel Romanczuk, from the Humboldt-Universität zu Berlin.

Reference paper

• Puy, A., Gimeno, E., Torrents, J., Bartashevich, P., Miguel, M. C., Pastor-Satorras, R., & Romanczuk, P. (2024). Selective social interactions and speed-induced leadership in schooling fish. Proceedings of the National Academy of Sciences, 121(18), e2309733121. https://doi.org/10.1073/pnas.2309733121