Growth rate variability in geographically diverse clones of Uronema (Ciliophora: Scuticociliatida)

Abstract Growth rates in 15 clones from the bacterivorous ciliate Uronema and one from Parauronema acutum have been compared under similar culture conditions. Five species were identified on a morphological basis: U. marinum, U. nigricans, U. elegans, P. acutum , and an undescribed form designated here as SWi1 . Intra- and inter-specific distinct growth characteristics were observed. Net cellular production tended to decrease with lower growth rate in different species or morphotypes but increased in those clones belonging to the same species. Growth rate and cell volume were not significatly correlated although mean growth rate increased with mean cell volume. Growth rate was however significantly correlated to the relative variation in cell volume between different growth phases. Estimation of growth rates using different models indicated that the experimental growth rates observed were not significatly different from those expected for the cell volumes. These results indicate how effects of habitat or geographical variability, in this cosmopolitan genus, may account for trophodynamic variation of morphologically similar species.