Ingestion rate decrease as the stimulus for sexuality in populations of Moina macrocopa1

The stimulus for the switch from asexual to sexual reproduction in populations of Moina macrocopa americana is an abrupt decrease in ingestion rate caused by a rapid reduction in the amount of available food. When nearly constant ingestion rates are maintained, through the addition of either nutritive or nonnutritive particles, asexual females do not produce any male or sexual female progeny. The stimulus seems to be physical in nature. Sexuality in the Cladocera can be attributed to a variety of environmental variables, all of which can significantly reduce ingestion rates.