Meeting Abstract
The origin of multicellular animals from a unicellular protozoan represents a pivotal transition in life’s history. We are using choanoflagellate protozoans (close relatives of animals) that can be unicellular and can form multicellular colonies as a model system to study functional consequences of being colonial vs. unicellular so that we can gain insights about selective factors that might have affected the evolution of multicellularity. Each choanoflagellate cell propels water by beating a single flagellum and captures bacterial prey on a collar of microvilli around the flagellum. We used high-speed microvideography to study the water flow produced by solitary cells and by colonies, and how that affects their ability to swim, to capture bacterial prey, and to be hydrodynamically-cryptic. We found that unicellular choanoflagellates swim more rapidly than colonies, which often rotate in place. The flux of water past cells tethered to each other in a colony is greater than for single cells, and cells in colonies capture more prey per time than do single cells. The larger the colony, the higher the prey capture rate per cell and the greater the differences between capture rates of the cells in a colony. However, there may be a trade-off between feeding performance and predator avoidance: the region of water disturbed by colonies is much bigger than the region disturbed by unicellular choanoflagellates, thus colonies put out larger hydrodynamic signals. Protozoans, both unicellular and colonial, play an important role in aquatic food webs. Using choanoflagellates as model organisms enables us to compare the trophic performance of uni- and multicellular forms within the same species, while also providing insights about ecological interactions that might have affected the evolution of multicellularity in the ancestors of animals.
