selfing

Selfing, short for self-fertilization, is a reproductive mode in which an organism fertilizes its own ovules with its own pollen or sperm. In plants, selfing typically refers to self-fertilization within a flower or from the same individual, and it contrasts with outcrossing, where fertilization occurs between distinct individuals. Selfing is common among many hermaphroditic plants but occurs in other organisms as well.

In flowering plants, selfing can occur via autogamy (self-pollination within a flower) or geitonogamy (pollination between flowers on the same individual). Mechanisms that promote selfing include temporal separation of male and female functions (dichogamy), floral traits that favor self-pollination (cleistogamy, or close proximity of anthers and stigma), and a transition from self-incompatibility to self-compatibility. Some species retain self-incompatibility and rely on outcrossing; others are predominantly selfing.

Genetic consequences of selfing are significant. Selfing rapidly increases homozygosity and the inbreeding coefficient, and reduces effective population size. This can lead to inbreeding depression, the reduced fitness of selfed offspring due to expression of recessive deleterious alleles. Over time, sustained selfing can purge some deleterious alleles, potentially reducing later inbreeding costs. Selfing also lowers genetic diversity and can slow adaptation to new environments, though it provides reproductive assurance when pollinators or mates are scarce.

Evolutionary context: transitions from outcrossing to selfing have evolved repeatedly. Selfing can facilitate reproduction in sparse populations or during colonization, but may limit long-term adaptive potential. The model plant Arabidopsis thaliana is highly selfing, and many crops exhibit mixed or predominant selfing.