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Durham University

Department of Biosciences


Publication details for Dr. Adrian Christopher Brennan

Silva, J.L., Brennan, A.C. & Mejías, J.A. (2016). Population genetics of self-incompatibility in a clade of relict cliff-dwelling plant species. AoB PLANTS 8: plw029.

Author(s) from Durham


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.