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The green alga Volvox swims by means of flagella on thousands of surface somatic cells. This geometry and its large size (diameter ~600 \mu m) make it a model organism for studying the fluid dynamics of multicellularity. Remarkably, when two nearby Volvox swim close to a solid surface, they attract one another and can form stable bound states in which they "waltz" around each other. This image shows a top-view of this state, obtained when the colonies swim up against a horizontal cover slip.
A surface-mediated hydrodynamic attraction combined with lubrication forces between spinning, bottom-heavy Volvox explains the formation, stability and dynamics of the bound states. These phenomena are suggested to underlie observed clustering of Volvox at surfaces.
Collaborators include: Knut Drescher (University of Cambridge), Kyriacos C. Leptos (University of Cambridge), Idan Tuval (University of Cambridge), Takuji Ishikawa (Tohoku University), Timothy J. Pedley (University of Cambridge), and Raymond E. Goldstein (University of Cambridge).
This research was supported by the Biotechnology and Biological Sciences Research Council, UK, the Human Frontier Science Program, the DOE, and the Schlumberger Chair Fund; and, was featured in the APS 2009 March Meeting Image Gallery and published in PRL April 20, 2009.
Physical Review Letters, "Dancing Volvox: Hydrodynamic Bound States of Swimming Algae"
March Meeting Image Gallery
Image Credit: Knut Drescher and Raymond E. Goldstein, University of Cambridge