Dietary Control of Sexuality in the Rotifer Asplanchna brightwelli Gosse

Abstract

Rotifers fed on paramecia in suspensions of Chlamydomonas or Euglena (> 50 cells per mm3) produced significant proportions of mictic female offspring. Those fed on pure paramecia produced only amictic females, irrespective of the population density (1-20 per ml) at which they were cultured. Starvation of newly born animals from mictic female producing cultures for 10-24 hr. did not affect the probability of their developing into mictic females. Mictic female production was sometimes associated with but not dependent upon changes in the fecundity and intrinsic rate of natural increase of the population. The activity of algal suspensions resided in the algal cells themselves. Cell free supertants of dense algal cultures were without effect. Acetone soluble material from Chlamydomonas, Euglena, and spinach leaves triggered mictic female production. It was assayed by preparing it in participate form and incorporating it into paramecia which were then fed to the rotifers. When amictic females with growing oocytes and embryos in different stages of development were transferred from pure paramecia to a diet containing Chlamydomonas, oocytes and embryos in developmental stages earlier than middle to late cleavage at the time of transfer were labile and could develop into mictic females. Embryonic stages in which organ differentiation could be observed were not affected by the dietary change. Since oocytes separate from the yolk gland before cleavage begins, mictic female production does not depend on the transfer of maternal cytoplasm into the egg. Rotifers continued to produce significant proportions of mictic females when maintained in algal suspensions for periods as long as 6 weeks. In one clone, rates of mictic female production soon declined under these conditions and stabilized at relatively low levels. This decline appeared to be irreversible and possibly caused by laboratory selection against the more sensitive animals in the population.