Aiden M. Stanley

Climate change has increased temperature and precipitation across the temperate northeast United States for almost two centuries, along with concurrent changes in ecological interactions, such as herbivory and pollination. Changes in floral traits such as flowering time, floral morphology, and reproductive allocation can disrupt pollination and reduce plant fitness, but plants with mixed-mating systems can limit fitness losses through self-pollination. However, although climatic, geographic, and ecological factors can affect plant phenotypes, their relative contribution is not well-established. Herbarium specimens preserve plant phenotypes that can establish trait change over broad spatial and temporal scales. We investigate the influence of climate change, geography, and ecological factors on flowering phenology, outcrossing flower morphology, and mating system expression in Impatiens capensis using 538 digitized images of time-stamped and georeferenced herbarium specimens collected over 120 years from Pennsylvania, USA. We found that temperature increased over this time period, and that flowering phenology advanced by 2.6 days/°C. Decreases in flower size were associated more with increased herbivory and geography than climatic factors. Outcrossing allocation decreased over time and across space, and this was only partially explained by increases in self-pollinating flower production westward and at higher elevations. Increasing temperature because of climate change advanced flowering phenology, but geographic and ecological factors are more important than climatic changes in determining outcrossing flower morphology and mating system allocation. However, as climate change continues to intensify, the relative importance of climatic, geographic, and ecological factors may shift, further impacting plant phenotypes and fitness.

Urbanization is a major human‐mediated driver of environmental change. Plants in urban environments may differ in timing and investment in key life history traits compared to rural plants as a result of genetic differentiation or plastic responses to the urban environment. However, it is unclear for many species whether genetic differentiation or plasticity has shaped urban phenotypes. Impatiens capensis is an annual plant that produces self‐pollinating and outcrossing flowers, varying in timing and amount based on environmental conditions. In this study, we characterized differences in floral phenology, mating system allocation, and key life history events between urban and rural populations of I. capensis , in situ and in greenhouse common gardens. We asked whether (1) floral investment varies with urbanization in situ, if (2) the differences between urban and rural populations are maintained (genetic differentiation) or lost/exaggerated (plasticity) in a common garden, if (3) differences can be attributed to shifts in life history strategy, and if (4) urban population traits are more variable (higher coefficient of variation). In situ, we found that urban populations advanced flowering time and invested more in outcrossing flowers compared to rural populations. Within greenhouse common gardens, urban plants maintained advanced flowering and were less variable than rural plants (low CV), indicative of genetic differentiation. In contrast, urban plants lost outcrossing bias in mating system allocation observed in situ, indicating plasticity, although both urban and rural plants were highly variable (high CV) for this trait. Early onset of selfing flowers was tied to earlier germination, but outcrossing onset was not affected by germination time. Flowering probability in urban plants was higher than rural ones in common gardens. Our study demonstrates that urbanization influences plant phenotypes through both genetic differentiation and phenotypic plasticity, but the relative importance of the two mechanisms of change vary among floral traits.

Mutualistic interactions between plants and animal pollinators are increasingly under threat through anthropogenic change, and it is critical to understand how temporal changes affect the structure and function of these ecologically important interactions. Because the responses of plant–pollinator interactions to anthropogenic change may take place over decades, historical collections that store information across long time horizons contribute uniquely to our understanding. In this article, we highlight several key questions related to long‐term changes in the structure and function of plant–pollinator interactions. We articulate how research could proceed rapidly via new techniques, greater integration of resources in museum collections along with coincident use of a single data source. We acknowledge the challenges that come with using historical collections and discuss how to minimize them. We provide suggestions that will allow for full utilization of museum resources for addressing a variety of issues regarding plant–pollinator interactions. This perspective paper aims to stimulate new integrative research aimed at understanding temporal patterns in plant–pollinator interactions. Read the free Plain Language Summary for this article on the Journal blog.

Pollen is a unique vehicle for viral spread. Pollen-associated viruses hitchhike on or within pollen grains and are transported to other plants by pollinators. They are deposited on flowers and have a direct pathway into the plant and next generation via seeds. To discover the diversity of pollen-associated viruses and identify contributing landscape and floral features, we perform a species-level metagenomic survey of pollen from wild, visually asymptomatic plants, located in one of four regions in the United States of America varying in land use. We identify many known and novel pollen-associated viruses, half belonging to the Bromoviridae, Partitiviridae, and Secoviridae viral families, but many families are represented. Across the regions, species harbor more viruses when surrounded by less natural and more human-modified environments than the reverse, but we note that other region-level differences may also covary with this. When examining the novel connection between virus richness and floral traits, we find that species with multiple, bilaterally symmetric flowers and smaller, spikier pollen harbored more viruses than those with opposite traits. The association of viral diversity with floral traits highlights the need to incorporate plant-pollinator interactions as a driver of pollen-associated virus transport into the study of plant-viral interactions.