Genome-wide genotyping in Tolpis succulenta

The mating system has profound consequences, not only for ecology and evolution, but also for the conservation of threatened or endangered species. Unfortunately, small populations are difficult to study owing to limits on sample size and genetic marker diversity. Here, we estimate mating system parameters in three small populations of an island plant using genomic genotyping. Although it is known that self-incompatible species often set some self-seed, little is known about how this affects mating system parameters or the role that multiple paternity plays in small populations. We generalize the BORICE mating system program to determine the siring pattern within maternal families. We applied this algorithm to maternal families from three populations of Tolpis succulenta from Madeira island and genotyped the progeny using RADseq. We applied BORICE to estimate each individual offspring as outcrossed or selfed, the paternity of each outcrossed offspring, and the level of inbreeding of each maternal plant. Despite a functional sporophytic self-incompatibility system, these data establish T. succulenta as a Pseudo Self Compatible (PSC) species. Two of 75 offspring were strongly indicated as products of self-fertilization. Despite selfing, all adult maternal plants were fully outbred. There was high differentiation among and low variation within populations, consistent with a history of genetic isolation of these small populations. There were generally multiple sires per maternal family. Twenty two percent of sib contrasts (between outcrossed offspring within maternal families) share the same sire.