Presentation Information
[C06-01]Swimming upstream while drawing helical trajectory: mathematical modeling of rheotaxis in basal relatives of vertebrates
*Ayumi Ozawa1, Oleg Tolstenkov2, Marios Chatzigeorgiou2, Tetsuya Hiraiwa3 (1. JAMSTEC (Japan), 2. University of Bergen (Norway), 3. Academia Sinica (Taiwan))
Keywords:
Rheotaxis,Tunicates,Circle swimmer,Chiral active Brownian particle
Some motile organisms tend to move with or against the current of the surrounding fluid. This behavioral response, called rheotaxis, can be advantageous for their survival. While neuronal and behavioral mechanisms of rheotaxis in vertebrates are extensively studied, relatively less is known outside of it, let alone how this behavior has evolved [1]. Here, we show that the larvae of Ciona intestinalis, one of the closest relatives of vertebrates, exhibit positive rheotaxis in the absence of visual cues and propose behavioral mechanisms behind it by combining experimental observation and mathematical modeling [2].
The experimental data indicated that the larvae achieved rheotaxis while drawing helical trajectories. Furthermore, they varied their heading speed and angular velocity according to the relative angle between the body axis and flow direction. Theoretical investigations with the use of mathematical models that account for this dependence indicate that the modulation of the angular velocity is the primary mechanism of the rheotaxis, while the modulation of the heading velocity also contributes to the rheotaxis.
Combined with whole-brain imaging of the larvae, these results propose how the larvae with a relatively simple nervous system can achieve rheotaxis by using solely mechanical information. More generally, this study extends our understanding of rheotaxis and will be a clue to trace back the evolution of the rheotaxis behavior.
[1] Wheeler, J. D., Secchi, E., Rusconi, R. and Stocker, R. Annual Review of Cell and Developmental Biology 35 (2019).
[2] Tolstenkov, O., Ozawa, A. et al. The cellular and behavioral blueprints of chordate rheotaxis. 2025.03.22.644710 Preprint at https://doi.org/10.1101/2025.03.22.644710 (2025).
The experimental data indicated that the larvae achieved rheotaxis while drawing helical trajectories. Furthermore, they varied their heading speed and angular velocity according to the relative angle between the body axis and flow direction. Theoretical investigations with the use of mathematical models that account for this dependence indicate that the modulation of the angular velocity is the primary mechanism of the rheotaxis, while the modulation of the heading velocity also contributes to the rheotaxis.
Combined with whole-brain imaging of the larvae, these results propose how the larvae with a relatively simple nervous system can achieve rheotaxis by using solely mechanical information. More generally, this study extends our understanding of rheotaxis and will be a clue to trace back the evolution of the rheotaxis behavior.
[1] Wheeler, J. D., Secchi, E., Rusconi, R. and Stocker, R. Annual Review of Cell and Developmental Biology 35 (2019).
[2] Tolstenkov, O., Ozawa, A. et al. The cellular and behavioral blueprints of chordate rheotaxis. 2025.03.22.644710 Preprint at https://doi.org/10.1101/2025.03.22.644710 (2025).