Native-range origin predicts genomic contribution in an experimental Mimulus guttatus invasion

Biological invasions and range expansions act as natural experiments for understanding evolutionary processes at and beyond a species' range margin. However, unlike manipulative experiments, invasions and range expansions are less genetically tractable and often involve genotypes of uncertain origin that are subject to complex evolutionary pressures. Here, we replay the earliest stages of the colonisation of the widespread North American plant species Mimulus guttatus (synonym Erythranthe guttata) in the United Kingdom. We established a common garden in the invaded range using northern and southern native genotypes, allowed plants to freely mate and recruit, and quantified the genomic contribution made after five growing seasons using whole genome pooled sequencing (Pool-Seq). Despite having lower genome-wide variation, northern genotypes contributed disproportionately to the experimental population, which showed a two-fold excess of northern relative to southern ancestry, with 63-70% northern contribution across chromosomes. The experimental population also showed extensive individual admixture, which we detected using diagnostic short sequences (k-mers) in the Pool-Seq data. Our results indicate that preadaptation of northern genotypes, despite reduced genome-wide variation, may have facilitated the successful range expansion of M. guttatus into the UK. This work also demonstrates how "invade and resequence" experiments can be used to dissect the genomic processes underlying expansion beyond a species' native range.