Experimental results on cell volume, growth rate, and macronuclear DNA variation in a ciliated protozoan

Some species of ciliated protozoans vary their body volume when fed on preys of different sizes. This peculiarity has offered us the opportunity to examine the relationship between changes in cell volume, amount of macronuclear DNA (maDNA), and cell division rates in subclones derived from a single clone of the ciliate Blepharisma japonicum (Order Heterotrichida). Our results demonstrate that food‐induced size changes in this single‐celled organism are accompanied by substantial changes in maDNA content and in reproduction (cell division) rate. We find a strong, direct linear correlation between cell volume and maDNA quantity, and an inverse linear correlation between cell volume and reproduction rate. No correlation between cell reproduction rate and maDNA amount was found. We conclude that food‐induced coordinate change in cell volume, maDNA content, and cell division rate in this organism may be an effective mechanism for rapid phenotypic change in response to variable environmental conditions.