Meeting Abstract
Comparative genomic and molecular phylogenetic evidence has revealed a close relationship between animals and choanoflagellate protozoans. Therefore, choanoflagellates that can form colonies are used as a model system to study mechanisms that may have been involved in the evolution of multicellularity in the ancestors of animals. For multicellularity to evolve, there may have been performance advantages that resulted in improved fitness for colonial organisms. This study explored predation as a potential selective pressure. The ciliated protozoan, Stentor coeruleus, was used as a model predator because its morphology is similar to that of ciliated protozoans that were abundant in the fossil record before animals evolved. Salpingoeca helianthica, a choanoflagellate with both unicellular and multicellular forms, was used as prey. High-speed videomicrography was used to record S. coeruleus preying upon S. helianthica. Videos were analyzed frame by frame to determine the feeding efficiency (number of prey captured per number encountered in the feeding current) of S. coeruleus for single-celled choanoflagellates vs. for colonies. Feeding efficiency was highest for unicellular prey and decreased significantly with number of cells in colonial prey. The mechanism responsible for better predation avoidance in colonial S. helianthica was that colonies escaped from the oral pouch of S. coeruleus more frequently than did single-celled choanoflagellates. These findings show that formation of multicellular colonies can improve the performance of choanoflagellates in avoiding predation, and suggest that predation might have been a selective factor in the evolution of multicellularity, a pivotal transition in life’s history.
