Hydrodynamic performance of choanoflagellate cells with flexible flagella and microvilli

A unicellular choanoflagellate has an ovoid cell body and a single flagellum surrounded by a collar of microvilli. By waving its flagellum, it swims and creates a water current that brings bacteria to its collar of microvilli. Alternatively, a thecate cell is not free swimming, but attaches itself to a substrate by a stalk that can deform with flow. Some choanoflagellates, like C. flexa, form colonies that are able to rapidly change their shape due to contraction of the microvilli apparatus. Detailed computational models of choanoflagellate hydrodynamics that capture body morphology typically assume rigid microvilli, rigid stalks, and prescribe the kinematics of the flagellum. However, the flagellum, microvilli, and stalks are not rigid structures, but flexible filaments whose evolving shapes are coupled to their fluid environment. We present a model that treats the flagellum and the microvilli as elastic Kirchhoff rods whose shapes are not pre-set, but emerge from the coupled system. In addition to understanding the effect of compliance of these structures on the swimming of a single organism, we will study the hydrodynamic interaction of two choanoflagellates and how the collars might affect this interaction.