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Phototactic Decision-Making by Microalgae
Shantanu Raikwar1, Adham Al-Kassem1, Nir S Gov2,3
1Laboratoire de Physique de l'École Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, F-75005 Paris, France.
Physical Review Letters
|December 12, 2025
Summary
Chlamydomonas reinhardtii algae navigate competing light stimuli using an intensity-weighted average of light directions. This strategy minimizes light exposure and arises from varied photoreceptor placement within the cell population.
Area of Science:
- Cell biology
- Biophysics
- Microbiology
Background:
- Unicellular algae like Chlamydomonas reinhardtii exhibit phototaxis, moving towards or away from light sources.
- Understanding decision-making in response to competing stimuli is crucial for simple organisms.
Purpose of the Study:
- To investigate how Chlamydomonas reinhardtii responds to multiple light sources with varying intensities and angles.
- To elucidate the underlying mechanisms and adaptive strategies governing phototaxis in competing light environments.
Main Methods:
- Experimental observation of Chlamydomonas reinhardtii behavior under dual-beam illumination.
- Development of a mathematical model to describe cell navigation based on light intensity and direction.
Main Results:
- Cells exhibit phototaxis following an intensity-weighted average of light propagation vectors when faced with two beams.
- This behavior aligns with an adaptive model that minimizes average light intensity at the cell's anterior pole.
- At large angular separations, cell populations split, with some cells exhibiting stochastic switching between different swimming directions.
Conclusions:
- The observed phototactic response is a geometrically determined law, representing an adaptive strategy for light avoidance.
- Population-level variations in photoreceptor distribution explain the observed behavioral diversity and front-back symmetry breaking.
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