  Many plants harbor complex mechanisms that promote outcrossing and efficient
pollen transfer. These include floral adaptations as well as genetic
mechanisms, such as molecular self-incompatibility (SI) systems. The
maintenance of such systems over long evolutionary timescales suggests that
outcrossing is favorable over a broad range of conditions. Conversely, SI has
repeatedly been lost, often in association with transitions to
self-fertilization (selfing). This transition is favored when the short-term
advantages of selfing outweigh the costs, primarily inbreeding depression. The
transition to selfing is expected to have major effects on population genetic
variation and adaptive potential, as well as on genome evolution. In the
Brassicaceae, many studies on the population genetic, gene regulatory and
genomic effects of selfing have centered on the model plant Arabidopsis
thaliana and the crucifer genus Capsella. The accumulation of population
genomics datasets have allowed detailed investigation of where, when and how
the transition to selfing occurred. Future studies will take advantage of the
development of population genetics theory on the impact of selfing, especially
regarding positive selection. Furthermore, investigation of systems including
recent transitions to selfing, mixed mating populations and/or multiple
independent replicates of the same transition will facilitate dissecting the
effects of mating system variation from processes driven by demography.
