title: The population genetics of sporophytic self-incompatibility in Senecio squalidus L. (Asteraceae): avoidance of mating constraints imposed by low S-allele number.
abstract: Senecio squalidus L. (Asteraceae) has been the subject of several ecological and population genetic studies due to its well-documented history of introduction, establishment and spread throughout Britain in the past 300 years. Our recent studies have focused on identifying and quantifying factors associated with the sporophytic self-incompatibility (SSI) system of S. squalidus that may have contributed to its success as a colonist. These findings are of general biological interest because they provide important insights into the short-term evolutionary dynamics of a plant mating system. The number of S-alleles in populations and their dominance interactions were investigated in eight wild British populations using cross-diallel studies. The numbers of S-alleles in British S. squalidus populations are typically low (average of 5.3 S-alleles) and the entire British population is estimated to possess no more than 7-11 S-alleles. Such low numbers of S-alleles are most probably a consequence of population bottlenecks associated with introduction and colonization. Potential evolutionary impacts on SSI caused by a paucity of S-alleles, such as restricted mate availability, are discussed, and we suggest that increased dominance interactions between S-alleles may be an important short-term means of increasing mate availability when S-allele numbers are low.
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
authors.forename: Adrian C
authors.initials: AC
authors.lastname: Brennan
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Harris
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Hiscock
mesh_terms: D000483:Alleles; D005799:Genes, Dominant / Q000235:genetics; D005828:Genetics, Population; D007178:Inbreeding; D012098:Reproduction / Q000235:genetics; D012674:Senecio / Q000235:genetics*; D006113:United Kingdom