Skip to main content
ARS Home » Midwest Area » Madison, Wisconsin » Vegetable Crops Research » Research » Research Project #434431

Research Project: Pollinators and Gene Flow

Location: Vegetable Crops Research

2020 Annual Report

Objective 1: Identify pollinator behaviors, pollinator management strategies, and crop production strategies that together mitigate unintended gene flow. Sub-objective 1.1: Pollinator behavior and plant reproductive strategies affect gene flow risk. Sub-objective 1.2: Visual and Olfactory cues that attract pollinators can guide the development of pollinator or crop management strategies that reduce gene flow and increase yield. Objective 2: Determine the impacts of cultivated carrot genes on the genomic landscape of wild carrot.

Objective 1. This objective is divided into two sub-objectives, each with three hypotheses to be tested. Sub-Objective 1.1. We will use a combination of field and greenhouse experiments to test the hypotheses within this subobjective. For example, the rules bees use when moving between patches or fields will be tested using patches of distinct sizes and isolation distances and measuring the number of transitions made by bees from a center glyphosate-resistant patch to the different conventional patches. The number of gene flow events in the different conventional patches, identified by the presence of glyphosate-resistant seeds, will also be used to test the decision making process of bumble bees. Greenhouse experiments will examine the pattern of seed deposition on flowers visited in succession by three bee species, honey bees, leafcutting bees and bumble bees. We will use glyphosate-resistant pollen donor and conventional pollen recipients and examine the number and proportion of glyphosate-resistant seeds on flowers visited in succession to determine the seed curve for each bee species. Sub-Objective 1.2. To determine the preference of each of three bee species to visual and/or olfactory cues, we will perform greenhouse experiments and quantify approaches and landings to different visual and/or olfactory cues. To identify a blend derived from nest cells that attract leafcutting bees, we will capture and identify the chemicals present in the bee cell using Gas Chromatography-Mass Spectrometry (GC-MS); determine whether there is a behavioral response and then use couple gas chromatography – electroantennographic detection (GC-EAD) to identify physiological responses. Finally, the electrophysiologically active constituents will be tested using a behavioral assay. Objective 2. We will use genotyping by sequencing on both cultivated carrots used in a breeding program and wild carrots in close proximity to the breeding area and far away to detect the presence of cultivated carrot genes in wild carrot populations. The presence of cultivated genes in wild populations represents introgression. We will determine the extent of introgression of cultivar genes in wild carrot populations.

Progress Report
Objective 1. ARS and Oakridge Institute for Science and Education (ORISE) scientists at Madison, Wisconsin, have completed greenhouse experiments to determine the pattern of seed deposition for flowers visited in succession by three bee species, the European honey bees, the alfalfa leafcutting bees and the common eastern bumble bee. Glyphosate-resistant pollen donors were used in the experiment and the number and proportion of glyphosate-resistant seeds were identified in successive flowers visited by the pollinators. These data are being analyzed to identify the seed curve for each of these three bee species. A manuscript has been written and submitted that summarizes the rules used by bumble bees when selecting patches. ARS and University of Wisconsin scientists at Madison, Wisconsin, reared leafcutting bees in the greenhouse and examined their behavior while foraging on alfalfa flowers. Objective 2. ARS and ORISE scientists at Madison, Wisconsin, collected carrot leaves from individuals in distinct populations over different states. We obtained genotyping by sequencing data on individuals from wild populations in Wisconsin, Iowa and Massachusetts. We performed further analyses to examine the extent of introgression of cultivar genes into wild carrot populations. A manuscript that compared trapping methods to identify pollinators of a crop species and quantify bee diversity was submitted. ARS and ORISE scientists completed the analyses of the genetic data collected from the 32 seed production fields and are preparing a manuscript summarizing these results. University of Georgia collaborators and ARS scientists at Madison, Wisconsin, are working out best methods to perform outcross crosses that produce few to none self-fertilize seeds.

1. Decision-making process of bees navigating discontinuous landscapes. Resources (pollen and nectar) are unevenly distributed over space and bees must make routing decisions when exploiting resources. A critical gap in our understanding of bee foraging over discontinuous landscapes is how they select patches or fields. To fill this gap, ARS, Oak Ridge Science and Education and University of Wisconsin scientists in Madison, Wisconsin, developed four mathematical models of patch attractiveness and tested predictions derived from these models against empirical data. Models differed in whether bees considered both resources and distance and whether they could fully or partially assess available resources when selecting a patch. Empirical data supported the model where bees utilized both resources and distance to select a patch and could assess the total resources available in a patch. Determining the decision-making process of bees when foraging permits the development of a conceptual and predictive framework to the study of bee movement. Such knowledge will guide the development of models to predict the movement of genetically engineered pollen carried by bees and will facilitate the design of habitats to ensure bee conservation.

2. The pattern of pollen foraging for two social bees. Honey bees and bumble bees are generalist eusocial bees that collect resources from a variety of plant taxa. Both bee species have distinct foraging strategies that affect patterns of resource collection, with implications for gene flow and for the design of pollinator-friendly habitats. ARS and University of Wisconsin researchers in Madison, Wisconsin, collected pollen from returning foragers of each bee species over five time periods and at three sites. They quantified the frequency of flower constant foragers, or foragers that collected a single pollen type in a foraging trip, and the richness and diversity of pollen collected by a colony. They explored bee preferences for pollen types by comparing the taxonomic identity of pollen collected to the resources available. Within a foraging trip, honey bees foraged on a single plant family more frequently than bumble bees throughout the summer, except during July, when both bee species had a similar frequency of flower constant foragers. Honey bees collected less diverse pollen relative to bumble bees and both bee species collected least diverse pollen in June. Bumble bees preferred some types of pollen and avoided other pollen, while honey bees foraged randomly and collected pollen based on the frequency of the plant morphotypes over the landscape. Therefore, the abundance of plant species over the landscape is expected to impact honey bee foraging more than bumble bee. Explicitly considering pollinator foraging strategy when designing agri-environment schemes will facilitate the development of pollinator friendly habitats and can inform on habitat design to reduce gene flow.

Review Publications
Brunet, J., Van Etten, M. 2019. The response of floral traits associated with pollinator attraction to environmental changes expected under anthropogenic climate change in high-altitude habitats. International Journal of Plant Sciences. 180(9):954-964.
Sapir, Y., Brunet, J., Byers, D., Imbert, E., Schonenberger, J., Staedler, Y. 2019. Floral evolution: Breeding systems, pollinators and beyond. International Journal of Plant Science. 180(9):929-933.
Guzman, A., Gaines-Day, H., Lois, A., Steffan, S.A., Brunet, J., Zalapa, J.E., Guedot, C. 2019. Surrounding landscape and spatial arrangement of honey bee hives affect pollen foraging and yield in cranberry. Agriculture, Ecosystems and Environment. 286:106624.
Palmieri Rocha, L., Ellison, S.L., Senalik, D.A., Simon, P.W., Brunet, J. 2020. Genetic markers to detect introgression of cultivar genes in wild carrot populations. Acta Horticulturae. 1264:165-174.