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Does urbanization affect natural selection on floral size in the spotted jewelweed?
Jérôme Burkiewicz, Jérémie Lavoie, Simon Joly
Urbanization has important impacts on wildlife. Amidst various effects, it can result in changes in the pollinator diversity, which could influence floral evolution by selecting floral features better adapted to the local pollinator community. In a previous study, we found that urban flowers of the spotted jewelweed (Impatiens capensis) were larger than the natural ones in the regions of Montreal and Quebec. Despite important phenotypic plasticity in the field, this genetic divergence was found to be significantly correlated with the size of its main pollinator – bumblebees. In this study, we test whether larger flowers have higher fitness in urban populations and if natural populations show an increase in reproductive success for smaller flowers. During the summers of 2023 and 2024, we sampled one pair of urban/natural populations of Impatiens capensis in the regions of Montreal and Quebec. We tagged 240 flowers, photographed them, and counted the seeds they produced as a measure of reproductive success. Selection gradients were used to assess if flower size is related to reproductive success. Although urban areas have been extensively studied in recent years, very few studies assessed natural selection in these environments. Our work provides insight on if and how natural selection acts in cities, and how Impatiens capensis overcame phenotypic plasticity to increase its reproductive success.
