Differential ability of three bee species to move genes via pollen

Authors: FRAGOSO, FABIANA - Oak Ridge Institute For Science And Education (ORISE); Brunet, Johanne

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2023
Publication Date: 4/13/2023
Citation: Fragoso, F., Brunet, J. 2023. Differential ability of three bee species to move genes via pollen. PLOS ONE 18(4). https://doi.org/10.1371/journal.pone.0271780.
DOI: https://doi.org/10.1371/journal.pone.0271780

Interpretive Summary: 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. In insect-pollinated crops, which include a variety of fruits and most vegetables for seed production, together with some forage and oil-producing crops, insects move pollen from flower to flower, and field to field. Here, we use glyphosate resistance (GR) as a genetic marker to examine whether distinct pollinators, bumble bees, honey bees and alfalfa leafcutting bees, affect how genes are moved via pollen. Leafcutting bees had the lowest probability of moving GR genes, followed by honey bees, and last bumble bees. 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. These results correlated with field-based gene flow estimates for honey bees and leafcutting bees. Differences in body size was a good predictor of the distance traveled by GR genes, and their respective tripping rate correlated with the number of GR seeds produced in an average foraging bout. The tripping rate is the proportion of flowers visited by a bee whose stigma and anthers are released during the visit and thus can be pollinated. Bee species vary in their tripping rate. These results indicate that bee species vary in their abilities to move genes via pollen. Such knowledge has important implications in agriculture where predicting the gene flow risk of different bee species can guide the development of pollinator management strategies to minimize the spread of genetically engineered (GE) genes. Such practices would lower adventitious presence and facilitate coexistence, in addition to minimize the transfer of GE genes to cross-compatible populations of feral or wild relatives and reduce their potential negative impact. Finally, this information can help bio regulators in their important task of refining the rules for isolation distances between fields pollinated by specific pollinators.

Technical Abstract: Gene flow is an important evolutionary force, and high gene flow tends to homogenize the genetic diversity of plant populations. In agriculture, 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. Distinct pollinators have been shown to affect plant reproductive success, pollen dispersal, and selection on floral traits. Here we examine whether distinct pollinators affect how genes are moved via pollen. We used Medicago sativa plants carrying three copies of the glyphosate resistance (GR) allele as pollen donors, and conventional plants as pollen recipients to describe the “seed curve” for each bee species. A seed curve illustrates the relationship between the probability of getting a GR 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. Different foraging metrics, including the number of GR seeds produced over a foraging bout, were also quantified and contrasted among bee species. Leafcutting bees had the lowest probability of moving GE genes, followed by honey bees, and last bumble bees. 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 results correlated with field-based gene flow estimates. Distinct pollinators have different abilities to move genes via pollen, which are affected by their body size and efficiency. Different bee species are thus expected to differentially impact gene flow in wild plant populations, and the spread of GE genes in insect-pollinated crops.