The evolution of self‐compatibility in geographically peripheral populations of Leavenworthia alabamica (Brassicaceae)

Self‐compatibility and adaptations to self‐fertilization are often found in plant populations at the periphery of species' ranges or on islands. Self‐compatibility may predominate in these environments because it provides reproductive assurance when pollinators or availability of mates limits seed production. This possibility was studied in Leavenworthia alabamica , a flowering plant endemic to the southeastern United States. Populations at the center of the species' range retain sporophytic self‐incompatibility, but peripheral populations are smaller, self‐compatible, and have adaptations for self‐fertilization. A reciprocal‐transplant experiment was designed to test whether there is pollen limitation of seed set and to examine its strength in central and peripheral populations. Self‐compatible genotypes produced more fruit and 17–22% more seed than self‐incompatible genotypes in all environments, suggesting that the transition to self‐compatibility may be favored by natural selection in all populations inhabited by L. alabamica . Sequence analyses demonstrated that two peripheral populations have 90–100% reductions in genetic variation, consistent with the effects of small population size or historical bottlenecks. Although pollen limitation of seed set occurs in all environments, self‐compatibility may evolve at the periphery in L. alabamica because the benefits of reproductive assurance are influenced by population size or bottlenecks following extinction and colonization.