On the maintenance of gynodioecy: Lewis' result extended

Abstract

The classical one-locus model of the maintenance of male sterile plants among hermaphrodites, first published by Lewis (1941) , is slightly modified and generalized to the case with an arbitrary number of sex determining loci, each with an arbitrary numbers of alleles. An essential feature of the model is that only fitness differences between sex phenotypes are considered. It is shown that the results of our population-genetic model differ from those of a phenotypic model, applied to this situation by Lloyd (1977) . Further, Lewis' model was extended to include overlapping generations so that the impact of differences between sexes in adult survival, i.e. in the number of seasons available for reproduction, on the frequency of male steriles could be studied. Small differences in adult survival may greatly affect sex ratio, and frequencies of male steriles higher than 50% are possible. The possibility of such differences has seldom been taken into account in experimental studies, although the majority of gynodioecious species have a perennial life habit. The problem in detecting survival rate differences among adults, especially in long lived species, is discussed.