Figure 1.

Self‐incompatibility is a textbook example of natural selection. Natural selection acts to remove nonfunctional variants in cases of strong inbreeding depression (as commonly observed in SI species such as A. lyrata, left, reproduced with permission from Sletvold, Mousset, Hagenblad, Hansson, & Agren, 2013). Even in populations devoid of SC variants, natural selection acts strongly by preventing fertilization between individuals expressing cognate specificities, hence causing negative frequency‐dependent selection on the genes controlling these specificities (right). The percentage of compatible mates is indicated for pollen expressing haplotypes with three contrasted frequencies, illustrating the rare‐allele advantage in this toy example