Variability of ingestion rates with stage in cell cycle of a heterotrophic nanoflagellate (Spumella Sp.) measured by an individual-based approach
Behavioural patterns and variability of feeding capacity during cell growth of a strain of the most common freshwater flagellate genus, Spumella (Chrysomonadida) were investigated. Individual cells and their daughter cells were continuously observed for 15 hours. Associated with the formation of a second pair of flagella the flagellates stopped feeding for 16 +/- 3 minutes during the phase of cell division. Non-feeding of individuals was related to cell division but not to any general inactivity of certain individuals. In contrast to ingestion, digestion proceeded during cell division and the food vacuoles were shared between the daughter cells. Cells stayed attached to the substratum even during cell division and the daughter cells already had a separate stalk before separation of the cell body started. Starvation synchronised the cells with respect to division. An initial shift in food concentration had a significant effect on the population feeding and growth rate even after three generations. The individual feeding capacity was positively correlated with cell size but increased roughly threefold whereas cell size doubled during cell growth. Due to these growth-phase-correlated differences in the individual ingestion rates, overall variability in the population ingestion rate was at least 47% (standard deviation) but decreased to ca. 10% when calculated from complete cell cycles as growth-phase-dependent effects were averaged. Growth-related feeding capacity may therefore account for flagellate subpopulations exhibiting different feeding regimes but only partly account for fractions of non-feeding or inactive individuals.
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