title: Population genetics of self-incompatibility in a clade of relict cliff-dwelling plant species.
abstract: The mating systems of species in small or fragmented populations impact upon their persistence. Small self-incompatible (SI) populations risk losing S allele diversity, responsible for the SI response, by drift thereby limiting mate availability and leading to population decline or SI system breakdown. But populations of relict and/or endemic species have resisted these demographic conditions over long periods suggesting their mating systems have adapted. To address a lack of empirical data on this topic, we studied the SI systems of three relict cliff-dwelling species of Sonchus section Pustulati (Asteraceae): S. masguindalii, S. fragilis and S. pustulatus in the western Mediterranean region. We performed controlled pollinations within and between individuals to measure index of SI (ISI) expression and identify S alleles in multiple population samples. Sonchus masguindalii and S. pustulatus showed strong SI (ISI = 0.6-1.0) compared to S. fragilis (ISI = 0.1-0.7). Just five S alleles were estimated for Spanish S. pustulatus and a moderate 11-15 S alleles for Moroccan S. pustulatus and S. fragilis, respectively. The fact that autonomous fruit set was generally improved by active self-pollination in self-compatible S. fragilis suggests that individuals with weak SI can show a wide range of outcrossing levels dependent on the degree of self or outcross pollen that pollinators bear. We conclude that frequent S allele dominance interactions that mask the incompatibility interactions of recessive S alleles leading to higher mate availability and partial breakdown of SI leading to mixed mating, both contribute to reproductive resilience in this group.
authors.affiliation: Departamento De Biología Vegetal Y Ecología, Universidad De Sevilla, Sevilla, CP 41012, España jlsilva@us.es.
authors.forename: Jose L
authors.initials: JL
authors.lastname: Silva
authors.affiliation: School of Biological and Biomedical Sciences, University of Durham, Durham, UK.
authors.forename: Adrian C
authors.initials: AC
authors.lastname: Brennan
authors.affiliation: Departamento De Biología Vegetal Y Ecología, Universidad De Sevilla, Sevilla, CP 41012, España.
authors.forename: José A
authors.initials: JA
authors.lastname: Mejías
keywords: Breakdown of SI; S allele diversity; Sonchus section Pustulati; diallel crosses; index of self-incompatibility; resilience; sporophytic self-incompatibility