Behaviour of a sex-differential fertility gene in hermaphrodite populations

Abstract

In genera of flowering plants that contain closely related gynodioecious and near dioecious species, near dioecy has probably evolved from gynodioecy by gradual reduction of seed set on hermaphrodites, caused by the action of several genes for partial female sterility. A literature survey shows that several types of sex-function differential fertility effects are widespread in hermaphrodite plants, so that a model of such variation may be of interest both as a model of normal hermaphrodite populations, and for the above evolutionary process. Such a model is presented where there is a dominant or non-dominant gene p for partial female sterility (ovule fertility values w3, w5 t1. Numerical results are given for equilibrium populations and include some cases of complete female sterility for comparison. These results show that frequencies of subhermaphrodites decrease with increased selfing. The heterozygous subhermaphrodite is the fittest, and the homozygous subhermaphrodite the least fit genotype. The fitness of the heterozygous subhermaphrodite decreases, and that of the hermaphrodite increases, with increased selfing. Except for males, proportions of ovule offspring decrease with increased selfing, and again with this exception and with t1 ≠ 1, t2 is highest for heterozygous subhermaphrodites, and for this type is > t1 whereas t2 is least for hermaphrodites. The total ovule production of the population increases, and total pollen production decreases, with increased selfing.