Meeting Abstract
Choanoflagellates, eukaryotes that are important predators on bacteria in aquatic ecosystems, share a common ancestor with sponges and are used as a model system to study the evolution of animals from protozoan ancestors. The choanoflagellate Salpingoeca rosetta, which has a complex life cycle that includes unicellular and multicellular stages, provides a model system to study within one species the functional consequences of: 1) different cell morphologies (swimming cell with a collar of prey-capturing microvilli surrounding a single flagellum; dispersal-stage cell with a slender body, long flagellum, and short collar), 2) being free-swimming vs. sessile (thecate cell attached to a surface), and 3) being a single cell vs. a multicellular colony. We used high-speed microvideography to measure swimming and feeding currents produced by different life stages, and computational fluid dynamics to study the effects of specific aspects of morphology on the fine-scale hydrodynamics of swimming and feeding. We found that a longer flagellum increases swimming speed, longer microvilli reduce speed, and cell shape only affects speed when the collar is very short. The flux of prey-carrying water into the collar capture zone is greater for swimming than sessile cells, but this advantage decreases with collar size. Stalk length has little effect on flux for sessile cells. Cells tethered to each other in colonies produce faster feeding currents and capture more prey per cell per time than do single cells, but there is a trade-off between feeding performance and predator avoidance because colonies produce larger hydrodynamic signals than do single cells.
