A multi-city examination of neutral and adaptive evolution in Impatiens capensis

Urbanization is a major driver of environmental change, yet the effects of city characteristics on neutral and adaptive evolution in plants remains poorly understood. We investigated evolutionary patterns in Impatiens capensis, a wildflower that can be found in many cities in eastern North America. We used genotype-by-sequencing to evaluate genetic variation, contemporary demographic history, and local adaptation across 10 cities in Ontario, Canada. Urbanization and city size shaped the amount of genetic diversity present in sites and contributed to fine-scale spatial genetic structure. We identified a signal of repeated population bottlenecks occurring across all cities that corresponded to the timing of rapid urban expansion in the region. City size was an important environmental driver of local adaptation among site, highlighting the role of cities on the adaptive evolution of populations. In addition to providing one of the first examples of parallel demographic shifts in response to urbanization, our results offer insights into why I. capensis may be particularly resilient to urbanization. Our findings emphasize the role that urban parks can play in maintaining genetic diversity and facilitating adaptation and suggest that prioritizing greenspace conservation is critical for supporting biodiversity in cities.