Patch selection by bumble bees navigating discontinuous landscapes

Authors: FRAGOSO, FABIANA - Oak Ridge Institute For Science And Education (ORISE); JIANG, QI - University Of Wisconsin; CLAYTON, MURRAY - University Of Wisconsin; Brunet, Johanne

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2021
Publication Date: 4/26/2021
Citation: Fragoso, F.P., Jiang, Q., Clayton, M.K., Brunet, J. 2021. Patch selection by bumble bees navigating discontinuous landscapes. Scientific Reports. 11. Article 8986. https://doi.org/10.1038/s41598-021-88394-2.
DOI: https://doi.org/10.1038/s41598-021-88394-2

Interpretive Summary: When pollinators collect pollen from one flower and deposit it on another flower, they move genes in the process. In insect-pollinated plants, pollinators can move genes via pollen between patches of plants and between crop fields. With the introduction of genetically engineered (GE) crops, limiting the movement of GE genes to fields destined to the organic or export markets has become a priority. Understanding pollinator foraging behavior can help us predict how far pollinators can move pollen over the landscape. Pollinators forage within a patch (or field) and then move to the next patch where they will continue moving pollen from flower to flower. Understanding the rules pollinators follow to select the next patch they will move to has been a difficult task. However, it is a crucial step if we are to link pollinator foraging behavior to gene movement. Here, we propose a novel approach to determine the rules bumble bees follow when moving between patches. We developed mathematical expression for each of four models of pollinator movement, each based on a different theory of patch attractiveness. To derive predictions from these models and test the different models, we designed an experiment with one central patch and four peripheral patches of two distinct sizes and distances from the center patch. Using the dimensions of the experiment, we assigned values to the variables of the models and derived predictions for each of the four models. We collected bee transition data from the center patch to each of the peripheral patches over two summers. To select the best model to explain bee behavior, we contrasted observed to predicted transition data. The best model indicated that bees considered both distance and total patch area when selecting a patch. Such a strategy optimizes energy gain as optimal foraging theory would predict. Our approach successfully identified how bumble bees selected the next patch they move to, information that is crucial to linking pollinator foraging behavior to pollinator movement, pollen dispersal and gene flow. This information is of interest to any researcher or the general public interested in bumble bee behavior. It is also of interest to the regulatory agencies dealing with GE crops and farmers and the industry because it will allow the development of models that better link bee foraging behavior to bee movement, pollen dispersal and gene flow.

Technical Abstract: Resources are unevenly distributed over space and bees must determine how to exploit such patchily distributed resources. Identifying the rules used by bees to select patches in a spatially variable environment has represented a daunting task. Here, we propose a simple and novel approach to identify the rules used by bees when navigating patchy resources and show how bumble bees use both distance between patches and patch size to select a patch. Bumble bees follow rules of optimal foraging when selecting patches and prefer nearby patches with more resources. We developed mathematical models of patch attractiveness and tested these models against empirical data. The mechanism highlighted in this study represents a major step towards understanding bee foraging over discontinuous landscapes. Such knowledge will improve the design of habitats to preserve bee populations and guide the development of models of bee movement in discontinuous landscapes to limit adventitious presence, or unwanted gene flow. These two issues have become imperative due to declining bee populations and the eminent release of new varieties produced via gene editing technologies for various insect-pollinated crops.