A model for the evolution of high frequencies of males in an androdioecious plant based on a cross‐compatibility advantage of males

Lloyd’s (1975) and Charlesworth & Charlesworth’s (1978) phenotypic selection models for the maintenance of androdioecy predict that males (female‐sterile individuals) must have an advantage in fertility ( K ) of at least two in order to invade a hermaphroditic population, and that their equilibrium frequency ( x eq =( K  − 2)/2( K −  1)) is always less than 0.5. In this paper, we develop a model in which male fertility is frequency‐dependent, a situation not investigated in the previous models, to explore the conditions under which a high frequency of males (i.e. more than 50%) could be maintained at equilibrium. We demonstrate that a gametophytic self‐incompatibility (GSI) locus linked to a nuclear sex determination locus can favour rare alleles through male function, by causing frequency‐dependent selection. Thus, the spread of a female‐sterility allele in a hermaphroditic population may be induced. In contrast with the previous models, our model can explain male frequencies greater than 50% in a functionally androdioecious species, as long as there is (i) dominance of female‐sterility at the sex locus, and (ii) a few alleles at the self‐incompatibility locus, even if the advantage in fertility of male phenotype is lower than two.