Control of sexuality in the rotifer Asplanchna brightwelli by dietary lipids of plant origin.

The relatively brief occurrences of sexual periods in Asplanchna and other pre- dominantly parthenogenetic rotifers of the order Ploima are the consequence of the parthenogenetic production of mictic rather than amictic females.Both types of females are diploid and similar in size and structure but differ in the kinds of eggs they lay.Amictic females lay eggs which produce one polar body during matura- tion, are diploid, and develop parthenogenetically into females.Mictic females lay eggs which produce two polar bodies during maturation, are haploid, and de- velop parthenogenetically into males if unfertilized, and into diploid, thick-walled resting eggs if fertilized.These low-temperature and desiccation-resistant eggs may resume development after diapause periods of variable length and always hatch into amictic females.Thus, as in many organisms, the sexual process results in the production of both new genotypes and inactive stages capable of withstanding ecologically unfavorable conditions.Many authors have reported that amictic females of the usually carnivorous, fresh-water zooplankter Asplanchna brightwelli tend to produce significant propor- tions of mictic female offspring when cultured in the presence of algae. 1-7A recent study by this author' indicates that the transition to mictic female production