Differences in particle size-dependent feeding efficiencies of closely related rotifer species

Size-selective feeding of four Brachionus strains was studied with three experimental setups: selection between polystyrene spheres of different sizes in short-term (10 min) feeding experiments, selection between pairs of dual-labeled algal taxa in short-term feeding experiments, and selection among three algal taxa in long-term (24 h) feeding experiments. Food size preferences were related to body sizes between strains but not within one strain (Brachionus calyciflorus). Brachionus angularis preferred food items <5-µm equivalent spherical diameter (ESD), Brachionus rubens strain F fed most efficiently on particles ∼5-µm ESD, and B. calyciflorus on particles of ∼10-µm ESD. Brachionus rubens strain B ingested particles from 3.5- to 12-µm ESD equally well. Apart from particle size effects, feeding was unselective. Polystyrene spheres of the appropriate sizes were ingested readily.