L. Ruth Rivkin

Urbanization is a major driver of environmental change that shapes the evolution of populations. However, the environmental differences amongst cities and their effects on neutral and adaptive evolution are less well understood. We investigated the contribution of city‐level variation to patterns of genetic evolution in Impatiens capensis , a native wildflower found in parks and green spaces in many cities across eastern North America. While the mixed mating system and flexible pollination requirements of I. capensis likely contribute to its resilience to urbanization, microenvironmental differences among cities may shape how this species evolves in cities. We used genotype‐by‐sequencing to evaluate genetic variation, contemporary demographic history, and genetic signatures of local adaptation in plants sampled from urban and rural sites across 10 cities in Ontario, Canada. Urbanization and city size shaped the amount of genetic diversity present at sites and were associated with fine‐scale spatial genetic structure. We identified a signal of repeated population bottlenecks across all cities, corresponding to the timing of rapid urban expansion in the region. City size was the environmental predictor most strongly associated with multilocus selection, highlighting the contribution of city variation to adaptive genomic evolution. Our findings provide one of the first examples of parallel demographic shifts in response to urbanization in plants and offer insights into why a native wildflower like 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 promoting urban biodiversity.

Knowledge of evolutionary patterns and genetic variation across a species' range is important for determining conservation and management strategies. The Arctic is the fastest‐warming ecosystem on Earth and has already reached temperature increases not expected in the rest of the world until the end of the century. Consequently, synthesizing patterns of evolutionary and genetic change in Arctic species will be instructive for understanding future change in other systems. Here, we present a literature review of peer‐reviewed published research exploring evolutionary processes in polar bears, a sentinel species for climate action. The wealth of knowledge generated from the long‐term monitoring of polar bears has provided data for exploring patterns of evolutionary change associated with climate change. Warming temperatures have led to significant reductions in sea ice coverage and availability, contributing to declines in genetic variation in some, but not all, polar bear subpopulations. Natural selection driven by warming and selective subsistence harvests may be contributing to the evolution of smaller body sizes in polar bears. However, evidence of adaptive change in polar bears remains limited, despite clear behavioral and phenological plasticity in the species in response to changing sea ice conditions. Following our review, we suggest pathways for identifying the effects of climate warming on the evolution and genetic variation in polar bears, which may improve strategies for locally supported conservation and management decisions. Our results highlight the general complexity of predicting the consequences of warming for wide‐ranging, genetically structured, and adaptively specialized species such as polar bears, and underscore the importance of developing evolutionarily informed management and conservation priorities for species threatened by climate change.

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.

The Arctic is warming four times faster than the rest of the world, threatening the persistence of many Arctic species. It is uncertain if Arctic wildlife will have sufficient time to adapt to such rapidly warming environments. We used genetic forecasting to measure the risk of maladaptation to warming temperatures and sea ice loss in polar bears (Ursus maritimus) sampled across the Canadian Arctic. We found evidence for local adaptation to sea ice conditions and temperature. Forecasting of genome‐environment mismatches for predicted climate scenarios suggested that polar bears in the Canadian high Arctic had the greatest risk of becoming maladapted to climate warming. While Canadian high Arctic bears may be the most likely to become maladapted, all polar bears face potentially negative outcomes to climate change. Given the importance of the sea ice habitat to polar bears, we expect that maladaptation to future warming is already widespread across Canada.

The polar bear (Ursus maritimus) is a species particularly vulnerable to the effects of climate change. As the climate warms, polar bears will be forced to move to more suitable habitats which are likely to shrink, adapt to the new conditions, or decline in population size. However, the genomic diversity within and among all 19 subpopulations of polar bears, and therefore their adaptive potential, is currently unknown. In addition, warmer climates are likely to result in more frequent contact between polar bears and grizzly bears (U. arctos), with which they can hybridize. Here we describe the development, quality control, and application of the Ursus maritimus V2 SNP chip. This 8 K SNP chip contains loci explicitly selected to assess both RAD-derived and transcriptome-derived loci, as well as SNPs to detect hybridization between species. A total of 7,239 loci (90.3% of those printed) were successfully genotyped, with over 99% genotype concordance for individuals typed in duplicate on this chip, and between individuals typed here and on the Ursus maritimus V1 SNP chip. Using simulations, we demonstrate that the markers have high accuracy and efficiency to detect hybridization and backcrosses between polar bears and grizzly bears. However, empirical analysis of 371 polar bears, 440 grizzly bears, and 8 known hybrids found no novel instances of recent hybridization. The Ursus maritimus V2 SNP chip provides a powerful tool for monitoring the adaptive potential of this species along with assessing population structure, quantitative genomics, and hybridization in polar bears.

The Arctic is warming four times faster than the rest of the world, threatening the persistence of Arctic species. It is uncertain if Arctic wildlife will have sufficient time to adapt to such rapidly warming environments. We used genetic forecasting to measure the risk of maladaptation to warming temperatures and sea ice loss in polar bears (Ursus maritimus) sampled across the Canadian Arctic. We found evidence for local adaptation to sea ice condition and temperature. Forecasting of genome-environment mismatches for predicted climate scenarios suggested that polar bears in the high Arctic had the greatest risk of becoming maladapted to climate warming. While bears in the high Canadian Arctic may be most likely to become maladapted, all polar bears face potentially negative outcomes to climate change. Given the importance of the sea ice habitat to polar bears, we expect that the increased risk of maladaptation to future warming is already widespread.

Urbanization is associated with numerous changes to the biotic and abiotic environments, many of which lead to a loss of biodiversity. Some studies have documented increased herbivory rates in cities, which has been hypothesized to lead to the evolution of novel defence traits in plants. Yet evidence supporting this hypothesis is contradictory and entirely absent from South American cities. To address this research gap, we evaluated herbivory rates in the native urban wildflower, Turnera subulata (Turneraceae), along an urbanization gradient in Joao Pessoa, Brazil. We predicted that higher rates of herbivory in cities would lead to the expression of cyanogenesis, a chemical defence found in a closely related Turnera species. We estimated herbivory rates and screened for cyanogenesis in 32 populations along the urbanization gradient, quantified by the Human Footprint Index and the amount of impervious surface surrounding each site. We found herbivory rates increased in T. subulata populations with increasing urbanization, but we did not find evidence of cyanogenesis in any of the populations. Our results suggest that although herbivores respond positively to urbanization, the fitness effects of leaf herbivory may be insufficient to select for the evolution of cyanogenesis in some plants. Our results provide valuable insight into the effects of urbanization on plant‐herbivore interactions in the tropics.

Although the field of urban evolutionary ecology has recently expanded, much progress has been made in identifying adaptations that arise as a result of selective pressures within these unique environments. However, as studies within urban environments have rapidly increased, researchers have recognized that there are challenges and opportunities in characterizing urban adaptation. Some of these challenges are a consequence of increased direct and indirect human influence, which compounds long‐recognized issues with research on adaptive evolution more generally. In this perspective, we discuss several common research challenges to urban adaptation related to (1) methodological approaches, (2) trait–environment relationships and the natural history of organisms, (3) agents and targets of selection, and (4) habitat heterogeneity. Ignoring these challenges may lead to misconceptions and further impede our ability to draw conclusions regarding evolutionary and ecological processes in urban environments. Our goal is to first shed light on the conceptual challenges of conducting urban adaptation research to help avoid the propagation of these misconceptions. We further summarize potential strategies to move forward productively to construct a more comprehensive picture of urban adaptation, and discuss how urban environments also offer unique opportunities and applications for adaptation research.