The Growth of Mixed Populations of Chilomonas paramecium and Tetrahymena patula

Abstract

ABSTRACT In mixed cultures, where Tetrahymena patula preys on Chilomonas paramecium, the growth of the Chilomonas population does not initially differ significantly from that in single cultures. Later, however, the decrease in numbers of Chilomonas is more rapid in mixed cultures, where it dies out after two months. The composition of the polymorphic Tetrahymena patula population depends on age and on the presence or absence of Chilomonas. Slitmouthed forms are absent at the beginning of growth in both mixed and single cultures, and only appear subsequently in mixed cultures. The percentage of these forms increases in older cultures. The percentage of microstomatous forms is larger, however, at the beginning of population growth, both in mixed and single cultures. The percentage of macrosto-matous forms increases from the beginning, reaches a maximum, and then decreases. Cannibalism has been observed in old mixed cultures. Significant differences in the size of individual organisms of Chilomonas between single and mixed cultures appeared from the beginning of the logarithmic phase of growth, and were pronounced up to the end of observations. Significant differences in the size of Tetrahymena patula between single and mixed cultures appeared somewhat later, from the sixth day onwards. The differences in size and shape between organisms in cultures of the same kind but of different ages were also significant. Variation in size and shape of both species was greater in mixed than in single cultures.