Loss of gametophytic self-incompatibility with evolution of inbreeding depression.
Gametophytic self-incompatibility (SI) in plants is a widespread mechanism preventing self-fertilization and the ensuing inbreeding depression, but it often evolves to self-compatibility. We analyze genetic mechanisms for the breakdown of gametophytic SI, incorporating a dynamic model for the evolution of inbreeding depression allowing for partial purging of nearly recessive lethal mutations by selfing, and accounting for pollen limitation and sheltered load linked to the S-locus. We consider two mechanisms for the breakdown of gametophytic SI: a nonfunctional S-allele and an unlinked modifier locus that inactivates the S-locus. We show that, under a wide range of conditions, self-compatible alleles can invade a self-incompatible population. Conditions for invasion are always less stringent for a nonfunctional S-allele than for a modifier locus. The spread of self-compatible genotypes is favored by extremely high or low selfing rates, a small number of S-alleles, and pollen limitation. Observed parameter values suggest that the maintenance of gametophytic SI is caused by a combination of high inbreeding depression in self-incompatible populations coupled with intermediate selfing rates of the self-compatible genotypes and sheltered load linked to the S-locus.
Porcher
Emmanuelle
E
Department of Biology, University of California-San Diego, La Jolla, California 92093, USA. eporcher@ucsd.edu
Lande
Russell
R
D000483:Alleles; D003433:Crosses, Genetic; D019143:Evolution, Molecular; D017343:Genes, Plant; D005854:Germ Cells; D007178:Inbreeding; D015810:Linkage Disequilibrium; D019684:Magnoliopsida / Q000235:genetics; D008957:Models, Genetic; D009154:Mutation; D011058:Pollen / Q000235:genetics