Ecological Studies on the Mechanism of Bisexual Reproduction in the Rotifer Brachionus plicatilis —I General Aspects of Bisexual Reproduction Inducing Factors

Abstract

The effects of external conditions and internal factors on bisexual reproduction were investigated. More mictic females appeared at 5 individuals/ml than at 1 individ./ml. Even when cultured individually, the animals put in 0.1 ml medium produced mictic females similarly as those cultured together. Mictic female production was effectively suppressed when the culture medium was renewed regularly. It might be concluded that mictic female production, which is one of the stages of bisexual reproduction, is a density dependent phenomenon. Furthermore, the efficacy of bisexual reproduction inducing factors increases in time throughout the course of the culture. It was suggested that some internal (innate or genetic) factors took part in bisexual reproduction, as deduced from the results that there were differences in the manner of mictic female production among mothers placed in identical environments. Accordingly in case that a massculture is maintained for a long term, only the strains that have less ability to reproduce bisexually are supposed to succeed because any individual in the identical strain has the same gene through parthenogenesis. Hereafter, adopting proper individuals should be the prerequisite for any experiment to study the inducing factors. © 1976, The Japanese Society of Fisheries Science. All rights reserved.