A conflict between two sexes, females and hermaphrodites.

We have reviewed models dealing with the maintenance of male-sterility under different modes of inheritance. For females to remain among hermaphrodites requires cytoplasmic information determining male-sterility and nuclear information restoring male-fertility. Such a nuclear-cytoplasmic polymorphism can be maintained at equilibrium given certain assumptions. However this equilibrium result may be irrelevant because gynodioecious populations are usually not at equilibrium, and because founder effects may give rise to high frequencies of females, due possibly to the fact that populations are often very different from one another genetically. The genetic structure of such a species depends on the frequency of females. Females are obligate outbreeders and usually produce more seeds than hermaphrodites. These two traits are beneficial to a group where females are present, in terms of effective size and seed output, although they are not, themselves, causes of the occurrence of females. Nuclear-cytoplasmic gynodioecy may lead to dioecy.