Ancient polymorphisms contribute to genome-wide variation by long-term balancing selection and divergent sorting in Boechera stricta

Background:
Genomic variation is widespread, and both neutral and selective processes can generate similar patterns in the genome. These processes are not mutually exclusive, so it is difficult to infer the evolutionary mechanisms that govern population and species divergence. Boechera stricta,is a perennial relative of Arabidopsis thaliana native to largely undisturbed habitats with two geographic and ecologically divergence subspecies. Here we delineate the evolutionary processes driving genetic diversity and population differentiation in this species.
Results:
Using whole genome re-sequencing data from 517 Boechera stricta accessions, we identify four genetic groups that diverged around 30 - 180 thousand years ago, with long-term small effective population sizes and recent population expansion after the Last Glacial Maximum. We find three genomic regions with elevated nucleotide diversity, totaling about 10% of the genome. These three regions of elevated nucleotide diversity show ...