Volvox are microscopic algae, spherical aggregates of thousands of flagellated cells. The spheres twirl about in ponds, swimming up and down in the water and interacting with their neighbours in seemingly orchestrated dances.
Physicist Raymond Goldstein of the University of Cambridge, UK, and his colleagues investigated the fluid dynamics used by Volvox carteri contained in a microscope-equipped chamber. Near the top of the chamber they observed the tiny dancers 'waltzing', spinning about each other in a clockwise fashion. Near the bottom, the spheres participated in a more complex 'minuet'.
The authors suggest that the careful dances increase female encounters with sperm packets during sexual reproduction.
For movies, see http://tinyurl.com/degwdj .