SUMMARY
Like many other species, the plant Arabidopsis thaliana has been introduced in recent history from its native Eurasian range to North America, with many individuals belonging to a single lineage. We have sequenced 100 genomes of present-day and herbarium specimens from this lineage, covering the time span from 1863 to 2006. Within-lineage recombination was nearly absent, greatly simplifying the genetic analysis, allowing direct estimation of the mutation rate and an introduction date in the early-17th century. The comparison of substitution rates at different sites throughout the genome reveals that genetic drift predominates, but that purifying selection in this rapidly expanding population is nevertheless evident even over short historical time scales. Furthermore, an association analysis identifies new mutations affecting root development, a trait important for adaptation in the wild. Our work illustrates how mutation and selection rates can be observed directly by combining modern genetic methods and historic samples.
HIGHLIGHTS
A historically young colonizing lineage of Arabidopsis thaliana allows observation of contemporary evolutionary forces.
Genomes from specimens collected over 150 years support direct calculation of mutation rates occurring in nature.
Drift predominates, but purifying selection is evident genome-wide over historical time scales.
New mutations with phenotypic effects can be identified and traced back in time and space.
