title: Genetic variation for pseudo-self-compatibility in self-incompatible populations of Leavenworthia alabamica (Brassicaceae).
abstract: Self-incompatibility (SI) promotes outcrossing, but transitions to self-compatibility (SC) are frequent. Population genetic theory describing the breakdown of SI to SC suggests that, under most conditions, populations should be composed of either SI or SC individuals. Under a narrow range of conditions, theory suggests that SI may persist alongside reduced expression of SI (pseudo-SI, PSI) in mixed-mating populations. We studied genetic variation for PSI segregating in four SI populations of Leavenworthia alabamica by measurement of the heritability of pollen tube number after self-pollination. We tested for the role of the S-locus in this variation by sequencing seven S-alleles from plants with high pseudo-SC (PSC) and testing for the co-segregation of these alleles with PSC. We found a continuous distribution of PSC in all populations and 90% of plants exhibited PSC. The heritability ranged from 0.39 to 0.57. All seven S-alleles from plants with high PSC exhibited trans-specific polymorphism, and no stop codons were observed within the c. 600-bp region sequenced. One of these S-alleles was directly associated with the inheritance of PSC. We conclude that heritable variation in PSC is largely a result of genetic variation in the signaling cascade downstream of the S-locus reaction, together with the presence of one leaky S-allele.
authors.affiliation: Department of Biology, McGill University, Montreal, QC, H3A 1B1, Canada.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Baldwin
authors.affiliation: Department of Biology, McGill University, Montreal, QC, H3A 1B1, Canada.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Schoen
mesh_terms: D000483:Alleles; D000704:Analysis of Variance; D019607:Brassicaceae / Q000235:genetics*; D014644:Genetic Variation; D005838:Genotype; D007178:Inbreeding; D040582:Inheritance Patterns / Q000235:genetics; D016014:Linear Models; D010641:Phenotype; D010802:Phylogeny; D053205:Pollen Tube / Q000502:physiology; D012044:Regression Analysis; D060436:Self-Incompatibility in Flowering Plants / Q000235:genetics*
keywords: 
  Leavenworthia alabamica
  ; S-alleles; heritability; plant mating systems; pollen tube growth; pseudo-self-compatibility; sporophytic self-incompatibility