THE EVOLUTIONARY SIGNIFICANCE OF PSEUDO-SELF-FERTILITY

The shift from self-sterility to predominant self-fertility has occurr ed in a multitude of flowering plant lineages. This shift has been att ributed to the partial replacement of self-incompatibility alleles at the S locus by alleles conferring self-fertility. I propose that pseud o-self-fertility (i.e., self-fertility dictated by polygenic modifiers of S gene action) may have been pivotal in the evolution of self-fert ility. Pseudo-self-fertility is known in numerous species, whereas sel f-fertility governed by S alleles is known only in a few species, and then only in those with a history of selfing. Pseudo-self-fertility is readily increased by selection, although its expression also is influ enced by the environment. Pseudo-self-fertility maximizes the dual adv antages of outcrossing and selfing.