At the Fourth International Volvox Meeting in St. Louis, a student from Harriton High School in Rosemont, Pennsylvania presented a talk and a poster on “flocking” behavior in Volvox barberi. Now a preprint describing his work is available on bioRxiv.
I can’t think of another time I’ve seen a high school student present at an international conference. It’s a bit unusual for undergraduates to present, but it’s certainly done. High school, though?
The preprint, by Ravi Balasubramanian, describes self-organized “flocks” of Volvox colonies, in some cases over 100 colonies. The flocks are essentially two-dimensional (one colony thick) and form just below the surface of the medium. Balasubramanian shows that they achieve nearly optimal packing, given that the colonies have a range of radii:
In mathematics, objects are considered optimally packed when they gather so that as many fit into a given space as possible…
I show here that V. barberi flocks have a log-normal distribution of colony radii, and form lattices which are nearly identical structurally to random close-packings in molecular dynamics simulations of weakly-attracting spheres with the same radius distribution. The characteristic feature of both the Volvox and simulation lattices is a log-normal distribution of lattice vertex angles. This shows that Volvox barberi gather into flocks that are near-optimally packed for their polydisperse radius distribution.
He also proposes a mechanism for the flocking behavior and provides evidence that this mechanism is at least consistent with the observations:
It is known that another species of Volvox – V. carteri is capable of using fluid forces created by flagellar beating to form waltzing pairs . I hypothesized that V. barberi, being one of the fastest species of Volvox , could exert similar attractive forces strong enough to pull V. barberi into well-packed sheets. To test for these attractive forces, a dye tracer was placed into culture wells containing either Volvox in medium or clear water (as a control).
Hopefully this work is in review somewhere; if so, I’ll provide an update when the final version is published.
Balasubramanian, R.N. 2018. Volvox barberi flocks, forming near-optimal, two-dimensional, polydisperse lattice packings. bioRxiv, 1–7. DOI: 10.1101/279059