DOI: 10.5061/dryad.ksn02v78q
title: The number of glyphosate resistant seeds produced by each of three bee species as they visit alfalfa flowers in sequence during a foraging bout

description: 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.
description: 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.