Collective enforcement of S‐ <scp>RNase</scp> ‐based self‐incompatibility

Previous models have attempted to explain the origin of new self-incompatibilities, whereas the model presented here explains the origin of new nonself-incompatibilities. Natural selection favors mutational changes to S-RNases that create nonself-incompatibilities with self-compatible (SC) haplotypes. By this means, an self-incompatible (SI) haplotype with a new S-RNase can avoid the costs of inbreeding imposed by an SC haplotype. The generation of new nonself-incompatibilities is countered by selection on SLF repertoires to increase the proportion of maternal haplotypes with which a paternal haplotype is compatible. The model predicts an evolutionary dynamic in which selection on SLF repertoires favors new compatibilities (including self-compatibility), but 'mutational adjustment' of S-RNases to the presence of SC haplotypes generates new nonself-incompatibilities. The relative frequencies of SI and SC haplotypes will be determined by the fluctuating balance, on the time-scale of new mutations, between these countervailing forces.