Population Genomics Reveals Demographic History and Climate Adaptation in Japanese Arabidopsis halleri.

Climate oscillations in the Quaternary forced species to major latitudinal or altitudinal range shifts. It has been suggested that adaptation concomitant with range shifts plays key roles in species responses during climate oscillations, but the role of selection for local adaptation to climatic changes remains largely unexplored. Here, we investigated population structure, demographic history and signatures of climate-driven selection based on genome-wide polymorphism data of 141 Japanese Arabidopsis halleri individuals, with European ones as outgroups.

The genetic architecture of the load linked to dominant and recessive self-incompatibility alleles in and .

The long-term balancing selection acting on mating types or sex-determining genes is expected to lead to the accumulation of deleterious mutations in the tightly linked chromosomal segments that are locally 'sheltered' from purifying selection. However, the factors determining the extent of this accumulation are poorly understood. Here, we took advantage of variations in the intensity of balancing selection along a dominance hierarchy formed by alleles at the sporophytic self-incompatibility system of the Brassicaceae to compare the pace at which linked deleterious mutations accumulate among them.

Dominance between self-incompatibility alleles determines the mating system of allopolyploids.

The shift from outcrossing to self-fertilization is one of the main evolutionary transitions in plants and has broad effects on evolutionary trajectories. In Brassicaceae, the ability to inhibit self-fertilization is controlled by 2 genes, and , tightly linked within the -locus. A series of small non-coding RNAs also encoded within the -locus regulates the transcriptional activity of alleles, resulting in a linear dominance hierarchy between them.

The homomorphic self-incompatibility system in Oleaceae is controlled by a hemizygous genomic region expressing a gibberellin pathway gene.

In flowering plants, outcrossing is commonly ensured by self-incompatibility (SI) systems. These can be homomorphic (typically with many different allelic specificities) or can accompany flower heteromorphism (mostly with just two specificities and corresponding floral types). The SI system of the Oleaceae family is unusual, with the long-term maintenance of only two specificities but often without flower morphology differences.

Long-Term Balancing Selection and the Genetic Load Linked to the Self-Incompatibility Locus in Arabidopsis halleri and A. lyrata.

Balancing selection is a form of natural selection maintaining diversity at the sites it targets and at linked nucleotide sites. Due to selection favoring heterozygosity, it has the potential to facilitate the accumulation of a "sheltered" load of tightly linked recessive deleterious mutations. However, precisely evaluating the extent of these effects has remained challenging.