Description of Research Area

A04: Synergy | Proposed Research Projects (2016-2017)

Kinematics of Phototaxis: Fluid Dynamics that Leads a Volvocine Green Alga towards Light


WADA, Hirofumi

Department of Physical Sciences, Ritsumeikan University

Research Subject

In this project, we will use theoretical approaches to obtain a quantitative understanding of phototactic ability of green algae, focusing on the recent experimental results on V. rousseletii as a model case [N. Ueki, et al BMCBiol (2010).]. Phototaxis refers to movements of organisms towards or away from a light source, and their mechanisms are diverse. In green algae phototaxis, a change of light intensity is a sensory input, and this information is processed to generate an output such that the swimming path is adjusted towards a light in a way governed by a fluid mechanics. This is a typical autonomous system in which a neither central nervous system nor intercellular communications is absent. We will compute translational and angular velocities of a Volvox colony from a profile of its surface fluid velocity field driven by the flagella beatings. This information is then integrated into three-dimensional kinematical equations that describe a trajectory of Volvox in presence and absence of a light source. In green algae, it is known that flagella response to illumination differs: V.carteri down-regulates flagella activity, V. rousseleti reverses its beating direction. We will perform a comparative study to explore how those differences of flagella regulation against light stimulus alter photoresponses of different kinds of algae based on our kinematic model, aiming to obtain evolutional implications of such differences. We will also explore, using the kinematic trajectory model, the robustness to noise, and possible advantages on the colony phototaxis of intrinsic fluctuations and variations in the photoresponse ability of individual somatic cells.

Research Partner

MURAYAMA, Yoshihiro
Division of Advanced Frontier Applied Physics,
Tokyo University of Agriculture and Technology
YOSHINAGA, Natsuhiko
Advanced Institute for Materials Research, Tohoku University
UEKI, Noriko
Laboratory for Chemistry and Life Science, Tokyo Institute of Technology
Grant-in-Aid for Scientific Research (KAKENHI) on Innovative Areas, MEXT, Japan
Synergy of Fluctuation and Structure : Quest for Universal Laws in Non-Equilibrium Systems