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  • Open Access

From Individual to Swarm Dynamics of Motile Photokinetic Organisms

J. Morales

P. Muñoz

D. Noto

H. N. Ulloa*

F. Guzmán-Lastra†

  • *Contact author: ulloa@sas.upenn.edu
  • †Contact author: fguzman@uchile.cl
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PRX Life 4, 023010 – Published 30 April, 2026

DOI: https://doi.org/10.1103/b3m3-2ffz

Abstract

The day–night cycle drives the largest biomass migration on Earth: the diel vertical migration (DVM) of aquatic organisms. Here, we present a three-dimensional agent-based model that incorporates photokinesis, gyrotaxis, and stochastic reorientation to explore how individual-level swimming behaviors give rise to population-scale DVM patterns. By solving Langevin equations for swarms of swimmers, we identify four distinct regimes—surface accumulation, shallow DVM, deep DVM, and sinking—governed by two key dimensionless parameters: the Péclet number (Pe), representing motility persistence, and the vertical swimming asymmetry ratio (W=wdown/wup), encoding photokinetic bias. These regimes emerge from nonlinear interactions between light-driven navigation and active noise, diagnosed through topological and statistical features of vertical distributions. A critical feedback is uncovered: upward-biased swimming (W<1) promotes surface aggregation, while excessive downward bias (W>1) leads to irreversible sinking. Analytical estimates link regime boundaries to gyrotactic alignment and velocity reversals. Together, our results provide a mechanistic framework to interpret DVM diversity and emphasize the central role of light gradients—beyond absolute intensity—in shaping ecological self-organization.

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PRX Life 4, 023010– Published 30 April, 2026
  • Received 23 June 2025
  • Accepted 6 April 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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