Introgression across ploidies contributes to genetic diversity in introduced urban <i>Capsella bursa-pastoris</i>

Successful establishment of a species in a new range is a useful way to understand the impact of demography and selection on the evolution of globally distributed species. In particular, introductions influence genetic diversity and population structure in the introduced range in unpredictable ways. Additionally, introgressive hybridization is often associated with successful establishment in new ranges. In this study, we explore the impact of introgressive hybridization on the polyploid <i>Capsella bursa-pastoris</i> in the New York City metropolitan area. We find <i>Capsella bursa-pastoris</i> in the New York City metropolitan area likely originated from multiple introductions from northern Eurasia, and that populations across the New York City metropolitan area are generally panmictic. As with <i>Capsella bursa-pastoris</i> in Eurasia, we discover evidence of introgression from the diploid <i>Capsella rubella</i> in this population. By evaluating ancestry in regions across the genome, we find introgressed regions are rich in gene content and contribute to genetic diversity in this population. These results suggest that introgressive hybridization before introductions may buffer species from the negative effects of population bottlenecks and allow for successful establishment.