Meeting Abstract

113.6  Saturday, Jan. 7  Swimming and Feeding by Unicellular vs. Colonial Choanoflagellates KOEHL, M. *; STOCKER, R.; NICOLAU, D.; KING, N.; Univ. of California, Berkeley; MIT; Univ. of California, Berkeley; Univ. of California, Berkeley

Many aquatic protozoans are unicellular, while others form multicellular colonies. We used Salpingoeca rosetta, a unicellular choanoflagellate that can be induced to form colonies, to study consequences to feeding of being unicellular vs. mulitcellular. Feeding by unicellular and colonial protozoans is not only ecologically important, but is also of evolutionary interest. Choanoflagellates are closely related to animals, and S. rosetta is a model organism in studies of the evolution of multicellularity. By using S. rosetta to study feeding performance, we explore a basic aspect of choanoflagellate biology that could have been an important selective factor during the evolution of multicellularity. A choanoflagellate cell swims with a single flagellum and eats bacteria captured on a collar of microvilli encircling the flagellum. Feeding performance depends: 1) encountering patches of prey, and 2) capturing bacteria from the water that flagellar beating moves past the choanflagellate. To study how S. rosetta encounter prey patches, we used a microfluidic device to put a stripe of high bacterial density in the water in a chamber where we could video S. rosetta swimming behavior. Colonies swim slowly in tight spirals, and thus hold their position in the water. In contrast, single-celled S. rosetta swim more rapidly along straighter paths, and can aggregate in the bacterial patch by turning more often once there. High-speed video revealed that the water currents produced by colonies are different from the flow around single cells, and feeding studies showed that colonies capture more prey per time than do single cells, A model of swimming and feeding behavior in which prey patchiness and shear due to ambient flow are varied reveals the types of habitats in which colonies vs. single cells show better feeding performance.