The number of glyphosate resistant seeds produced by each of three bee species as they visit alfalfa flowers in sequence during a foraging bout
Data files
Mar 28, 2023 version files 319.46 KB
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Data_for_seed_curves_last_all_bees.csv
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README.md
Abstract
Since the release of genetically engineered (GE) crops, there has been increased concern about the introduction of GE genes into non-GE fields of a crop and their spread to feral or wild cross-compatible relatives. More recently, attention has been given to the differential impact of distinct pollinators on gene flow, with the goal of developing isolation distances associated with specific managed pollinators. To examine the differential impact of bee species on gene movement, we quantified the relationship between the probability of getting a GE seed in a pod, and the order in which a flower was visited, or the cumulative distance traveled by a bee in a foraging bout. We refer to these relationships as ‘seed curves’ and compare these seeds curves among three bee species. The experiments used Medicago sativa L. plants carrying three copies of the glyphosate resistance (GR) allele as pollen donors (M. sativa is a tetraploid), such that each pollen grain carried the GR allele, and conventional plants as pollen recipients. Different foraging metrics, including the number of GR seeds produced over a foraging bout, were also quantified and contrasted among bee species. The lowest number of GR seeds set per foraging bout, and the GR seeds set at the shortest distances, were produced following leafcutting bee visits. In contrast, GR seeds were found at the longest distances following bumble bee visits. Values for honey bees were intermediate. The ranking of bee species based on seed curves correlated well with field-based gene flow estimates. Thus, differential seed curves of bee species, which describe patterns of seed production within foraging bouts, translated into distinct abilities of bee species to move genes at a landscape level. Bee behavior at a local scale (foraging bout) helps predict gene flow and the spread of GE genes at the landscape scale.
Methods
The experiments were carried out inside cages set up in a greenhouse room at the University of Wisconsin Walnut Street Greenhouse in Madison, WI, USA. A smaller 2.0 x 2.0 x 1.8 m cage adjoined a larger 4.0 x 2.0 x 1.8 m cage (Fig 1). The frames of the cages were made of PVC tubing and were covered with mosquito netting (Skeeta, Inc., Bradenton, FL, USA) which was also used to separate the two adjacent cages. Glyphosate-resistant (GR) alfalfa plants, also known as Roundup Ready (RR) alfalfa, were placed in the small cage and used as pollen donors in the experiment. Conventional alfalfa plants were placed in the large cage and used as pollen recipients.
The GR plants used as pollen donors had a single copy of the GR gene, and at least three copies of the GR allele. Because alfalfa is a tetraploid, all pollen grains of plants with at least three copies of the GR allele will carry at least one GR allele. Because the GR allele is dominant, one copy of the gene suffices for the expression of glyphosate resistance in the seeds and seedlings. While the GR gene is hemizygous when inserted, crosses are made between plants to increase the number of copies of the GR allele in plants that carried only one inserted copy of the GR gene. The number of gene and allele copies is verified by the proportion of GR seeds produced in crosses and via quantitative PCR.