Differential ability of three bee species to move genes via pollen

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 travelled 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, 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. Leafcutting bees produced the lowest number of GR genes in a foraging bout, and moved them the shortest distances, bumble bees the longest. Values for honey bees were intermediate. Seed curves correlated with field-based gene flow estimates. Thus, differential seed curves of bee species, reflecting within foraging bout patterns, translated into distinct abilities of bee species to move genes at a landscape level. Differences in seed curves reflected differences in foraging behavior among bee species, and helped explain their differential impact on gene flow and the spread of GE genes in insect-pollinated crops.