The genetic consequences of contrasting breeding systems in Plectritis (Valerianaceae)

Isozyme variation at 12 loci was analyzed in 10 populations of Plectritis brachystemon and 15 populations of P. congesta, two related species of annual plants that differ primarily in floral characters. They have similar life-history strategies and habitat requirements and often occur sympatrically. Plectritis brachystemon is highly autogamous, with an average outcrossing rate of 2%, while P. congesta is predominantly allogamous, with an average outcrossing rate of 70%. All measures of genetic variation within populations showed that the outcrossing species maintained significantly more genetic variation within populations than did the selfing species. Most of the gene diversity in the selfing species, P. brachystemon, was interpopulational, while most of the diversity in the outcrossing species, P. congesta, was intrapopulational. The differences in genetic variability within populations of these species and in the genetic structure of these species are primarily the result of their contrasting breeding systems.