Investigating past range dynamics for a weed of cultivation, Silene vulgaris

Since the last glacial maximum (LGM) ~21 kya, when colder climates and ice sheets restricted most European taxa to southern regions, the warming climate has allowed certain species to colonize previously unsuitable regions. This phenomenon of post-glacial expansion from glacial refugia has been documented in studies of numerous plant and animal taxa. During contemporary biological invasions, species also experience dramatic range expansions but by very different mechanisms. For example, human mediated dispersal may allow species to expand into suitable, but previously unoccupied, sites. Weeds of cultivation may have spread globally following the expansion of agriculture and/or ruderal habitats associated with human-mediated disturbance. In this thesis, I tested whether the range expansion of Silene vulgaris across Europe fit the classical model of post-glacial expansion from southern refugia, or followed known routes of the expansion of human agricultural practices. I used Species Distribution Modeling (SDM) to predict patterns of post-glacial expansion and contrasted these with the patterns of human agricultural expansion. A population genetic analysis using microsatellite loci was then used to test which scenario was better supported by spatial patterns of genetic diversity and structure. Genetic diversity was highest in Southern Europe and declined with increasing latitude, and locations of ancestral demes from genetic cluster analysis were consistent with areas of predicted refugia. These results support post-glacial colonization while refuting the East to West agricultural spread as the main mode of expansion for S. vulgaris. We know that Silene vulgaris has recently colonized many regions (including North America and other continents) via human-mediated dispersal, but there is no evidence for a direct link between the Neolithic expansion of agriculture and current patterns of genetic diversity in Europe. Therefore, S. vulgaris likely participated in a long history of post-glacial expansion since the Last Glacial Maximum, but has since spread around the globe by other means.