Gynodioecy in Plantago maritima L.; no compensation for loss of male function

Size, allocation of biomass, seed production of hermaphrodites and male steriles as well as germination, growth rate and survival among their progeny were compared between male fertile and male sterile cytoplasmic genotypes of Plantago maritima. The cytoplasmic genomes in angiosperms are predominantly maternally inherited. Thus we used the progeny originating from the male fertile and male sterile mothers in order to examine the relative success of the mothers. The progeny was grown together at three different densities in a greenhouse competition experiment. The results were analysed in a hierarchical model with siblings as replicates of mothers and mothers as replicates of sex-morphs. Differences between sex morphs were very small, but they were consistent in that the progeny from male steriles always performed less well than did the progeny from hermaphrodites. Male sterile progeny matched the hermaphrodite progeny best at the lowest density, where there was no effect of sex type on the level of individual performance. One explanation why hermaphrodites perform relatively better at higher densities could be that they are more plastic in their response to competition induced stress. This was indicated by density dependent allocation pattern of biomass to different parts of the plants, where the progeny of hermaphrodites appeared to be more plastic. The results from this experiment, and other studies, supports the idea that male sterility, if nucleo-cytoplasmically determined, can persist in a population even without any fitness advantages for females.