The evolution of dominance in sporophytic self-incompatibility systems. II. Mate availability and recombination.
Sporophytic self-incompatibility (SSI) is a self-pollen recognition system that enforces outcrossing in plants. Recognition in SSI systems is typically controlled by a complex locus (S-locus) with separate genes that determine pollen and stigma specificity. Experimental studies show that S-alleles can be dominant, recessive, or codominant, and that the dominance level of a given S-allele can depend upon whether pollen or stigma specificity is examined. Here and in the companion paper by Llaurens and colleagues, the evolution of dominance in single-locus SSI is explored using numerical models and simulation. Particular attention is directed at factors that can cause S-allele dominance to differ in pollen versus stigma. The effect of recombination between the S-locus and modifier locus is also examined. The models predict that limitation in the number of compatible mates is required for the evolution of S-allele dominance in the stigma but not in the pollen. Tight linkage between the S-locus and modifier promotes the evolution of S-allele dominance hierarchies. Model results are interpreted with respect to published information on the molecular basis of dominance in SSI systems, and reported S-allele dominance relationships in a variety of species. These studies show that dominant S-alleles are more common in the pollen than in the stigma, a pattern that when interpreted in light of model predictions, suggests that mate limitation may be relatively infrequent in natural populations with SSI.
Schoen
Daniel J
DJ
Department of Biology, McGill University, Montreal Québec, Canada. daniel.schoen@mcgill.ca
Busch
Jeremiah W
JW
D000483:Alleles; D005075:Biological Evolution; D006239:Haplotypes; D019684:Magnoliopsida / Q000235:genetics* / Q000254:growth & development; D009154:Mutation; D010641:Phenotype; D054817:Pollination; D011110:Polymorphism, Genetic; D011995:Recombination, Genetic