Resurrection genomics reveals rapid genetic change in natural Brassica rapa populations following drought. Brassica rapa

Genetic responses to selective events are rarely documented in the wild. We analyzed genome-wide differences between ancestors and descendants of two natural populations of Brassica rapa plants that rapidly evolved changes in multiple phenotypic traits following a 6 yr drought. We found many highly differentiated (FST outlier) genes between ancestors and descendants, including some related to drought stress and flowering time. This result reveals multiple genes that evolved over the course of the drought, potentially in response to this selective event. There was little overlap in genes found with outlier FST analysis and with site frequency spectrum (SFS) analysis, indicating that these different approaches are likely sensitive to selection acting at different temporal scales. Thus the resurrection genomics approach we used appeared able to detect recent evolutionary shifts that could have been missed by SFS analysis. Few loci were outliers in both populations, suggesting independent genetic trajectories of evolution.