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Insects are important pollinators for many fruit, vegetable, forage, and oil-seed crops. Because many of these crops are visited and pollinated by wild pollinators, in addition to managed pollinators, it is important to consider the impact of different pollinators on gene flow. This has become especially important when considering the potential for transgene escape from genetically modified crops. As a first step, we used the Rocky Mountain columbine (Aquilegia coerulea) to establish that distinct pollinators differentially disperse pollen. We showed that distinct pollinators can differentially affect the outcrossing rate of plants (Brunet and Sweet, Evolution, 2006) and, using genetic markers, that these different pollinators may differentially move pollen long distances (Brunet and Holmquist, Molecular Ecology, 2009). In addition, we have shown that features of the landscape may differentially affect gene flow for distinct pollinators (Brunet and Stewart, Psyche: A Journal of Entomology, 2010).
To expand these studies, we are using alfalfa (Medicago sativa) in an agricultural setting, where landscape features can be manipulated. Honey bees and leaf cutting bees are used as managed pollinators of alfalfa in seed production fields. Bumble bees also visit alfalfa fields (Brunet and Stewart, 2010). We are examining how different pollinators forage in alfalfa fields and how they move pollen around. We are looking at features of the alfalfa landscape such as patch size and isolation distances between patches that affect bee movement within and among patches. Our ultimate goal is to link pollinator behavior to gene flow in order to make a more predictive model of gene flow by insect pollinators. In collaboration with Dr. Murray Clayton in the departments of Statistics and Plant Pathology at the University of Wisconsin in Madison, we are developing a simulation model that links pollinator behavior to gene flow over the agricultural landscape. Such model will help predict gene flow and the risk of transgene escape for alfalfa seed production fields and for other insect-pollinated crops. We are looking at patterns of pollinator movements, at how pollinators move pollen as they forage between flowers and at the factors that affect the probability that the pollen deposited on the stigma will generate viable seeds. We are building models for pollinator movements, pollen dispersal and for gene flow (seed set). We are examining pollinator foraging range and how it is affected by resource availability. In these studies, we are interested in identifying the plant traits, including floral volatiles, that are most attractive to honeybees, leaf cutting bees and bumble bees. We are examining how these three pollinators affect the plant mating system (Riday et al. 20015) and how this impacts inbreeding and gene flow. We are examining the impact of distinct pollinators on pollen dispersal curves and gene flow. Our studies combine various approaches including ecology, genetics, pollinator behavior and modeling.
Earlier studies with A. coerulea demonstrated that selfing in this plant species is most likely a non-adaptive consequence of having more than one flower open at the same time on a plant (Brunet and Sweet Evolution, 2006; International Journal of Plant Sciences, 2006). We have quantified the variation in pollination biology and floral traits among populations over part of the range of A. coerulea (Brunet, Annals of Botany, 2009). We have examined the impact of pollination and mating system on the geographical variation in genetic structure of A. coerulea populations (Brunet et al. IJPS 2012). In collaboration with Ken Keefover-Ring, we are examining the floral scent of this plant species and how they affect bumble bees and hawkmoths, the two major pollinators of this plant species. We are also examining pollinator behavior and Margaret Thairu, a Master student in the laboratory, recently finished a study examining the role of pollinators in maintaining flower color variation within and among A. coerulea populations (Thairu and Brunet Annals of Botany 2015).
Insect pollinators are vital to both natural and agricultural systems. Although the European honeybee is the most commonly managed pollinator in U.S. agricultural systems, wild bee species contribute to crop pollination as well. Native, wild bees are highly diverse, occur in many habitats, and are active throughout the growing season under a diversity of conditions. They also provide a pollination service to growers that is free of charge. The intensification of agricultural practices, herbicide and pesticide use, and the simplification of our landscapes have made life more difficult for honeybees and native pollinators. We have yet to fully understand how much native bees bolster crop yields in Wisconsin, or how certain management practices help or hurt their populations. To better understand these questions we partner with Wisconsin apple and cranberry growers, the Wisconsin Department of Natural Resources and the US Fish and Wildlife Service.