Filter-feeding in Colonial Protists.

Many protists form cell colonies. Among them several are filter-feeders depending on suspended food particles such as bacteria. It has been suggested that the formation of colonies enhances feeding efficiency and implied that - in the case of colonial choanoflagellates - it was an adaptive trait that led to the evolution of metazoans. Here it is shown experimentally - for a colonial peritrich ciliate and for a choanoflagellate - that colony-formation does not enhance the efficiency of filter-feeding relative to solitary cells and that the adaptive significance of cell colony-formation must have some other explanation.