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.