Urbanization is a major driver of environmental change that shapes the evolution of populations. However, the effects of environmental differences among cities on neutral and adaptive evolution remains poorly understood. We investigated evolutionary patterns in Impatiens capensis, a native 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 at 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 predictor of local adaptation, highlighting the role of cities in driving the adaptive evolution of populations. Our findings provide one of the first examples of parallel demographic shifts in response to urbanization in plants and offer insights into why I. capensis may be particularly resilient to urbanization. Taken together, our results emphasize the role that urban parks can play in maintaining genetic diversity and facilitating adaptation, suggesting that prioritizing greenspace conservation is critical for maintain urban biodiversity.

Urban evolutionary biology is the study of rapid evolutionary change in response to humans and our use of lands to support city dwellers. Because cities are relatively modern additions to the natural world, research on urban evolution tends to focus on microevolutionary change that has happened across a few to many hundreds of generations. These questions still fall under the broad purview of evolutionary ecology. But the severity, rapidity, and replication of environmental changes that drive evolution in this context make it worthy of specific attention. Urban evolution provides the opportunity to study the earliest stages of evolution in a context that is scientifically interesting and societally important. The newness of urban populations and their proximity to natural populations also creates challenges when trying to detect population genetic change. In a From the Cover article in this issue of Molecular Ecology, Mueller et al. (2020) use whole genome resequencing data to address some of these challenges while exploring genetic changes associated with urbanization in 3 replicate urban-rural burrowing owl (Athene cunicularia) populations. Combining multiple approaches across these sample sites Mueller et al. find evidence for selection on genes whose function is related to synapses, neuron projections, brain connectivity, and cognitive function in general. That selection was parallel suggests brain processes were likely important for urban adaptation.