Bee species perform distinct foraging behaviors that are best described by different movement models

Authors: Brunet, Johanne; JIANG, QI - University Of Wisconsin; ZHAO, YANG - University Of Wisconsin; THAIRU, MARGARET - University Of Wisconsin; CLAYTON, MURRAY - University Of Wisconsin

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2022
Publication Date: 1/2/2023
Citation: Brunet, J., Jiang, Q., Zhao, Y., Thairu, M.W., Clayton, M.K. 2023. Bee species perform distinct foraging behaviors that are best described by different movement models. Scientific Reports. Article 71.. https://doi.org/10.1038/s41598-022-26858-9.
DOI: https://doi.org/10.1038/s41598-022-26858-9

Interpretive Summary: The predicted increase in genetically engineered (GE) crops, resulting from gene editing technologies, makes limiting the movement of GE genes to fields destined to the organic or export markets and to wild populations an important priority. In insect-pollinated plants, pollinators can move genes via pollen within and among plants and fields. A better understanding of how pollinator foraging behavior affects pollinator movement, for distinct bee species, would improve our predictions of how far distinct pollinators can move genes over the landscape. In this study, we examined the foraging behavior of three bee species, the European honey bee, Apis mellifera, the common eastern bumble bee, Bombus impatiens, and the alfalfa leafcutting bee, Megachile rotundata visiting alfalfa (Medicago sativa) flowers. Using the resulting distance and direction data, we developed and compared four different models of bee movement for each bee species. The models simulated a bee moving a given distance and direction from raceme to raceme within a foraging bout. A foraging bout includes all the racemes visited by a bee from the time it enters and leaves a patch. The models differed in how the distances and directions traveled between consecutive racemes were selected. For the random distance or random direction model, distances or directions were selected from the empirical distributions of distances or directions. For the modeled distance model, distances were derived from the best model for distance and for modeled direction, transitions probabilities were used to select directions. The Modeled Distance-Modeled Direction model best predicted bumble bee movement. For leafcutting bees, a Random Distance-Random Direction model was favored. If we assume the lower sample sizes provided lower power to discriminate among models, the Modeled Distance-Modeled Direction would best describe honey bee movement. We calculated and compared net distances traveled by each bee species, based on these best movement models. We obtained the shortest net distances traveled by leafcutting bees, followed by honey bees and the longest distances for bumble bees. The predicted ranking for leafcutting bees and honey bees is supported by empirical gene flow data. This study provides a mechanistic explanation for the lower gene flow distances by leafcutting bees and the approach developed here can be extended to other crops and their pollinators. Linking pollinator foraging behavior to pollinator movement can guide the design of pollinator strategies to minimize gene flow and facilitate coexistence in agricultural crops. Results of this study will benefit farmers, the alfalfa industry, and bioregulators interested in limiting adventitious presence (unwanted gene flow) and facilitating coexistence.

Technical Abstract: Linking animal behavior to models of animal movement has been an important, yet challenging goal for animal ecologists. In insect-pollinated plants, the foraging behavior of pollinators can influence their movement and ultimately affect how genes, including genetically engineered (GE) genes, are moved via pollen. We recorded the fine scale movement of three bee species foraging in patches of alfalfa (Medicago sativa), the European honey bee, Apis mellifera, the common eastern bumble bee, Bombus impatiens, and the alfalfa leafcutting bee, Megachile rotundata. Using the resulting distance and direction data, four models of bee movement were compared for each bee species. Each model simulated a bee moving a given distance and direction between consecutive racemes during a foraging bout. The models differed in whether the distance or direction traveled between consecutive racemes were randomly selected from the empirical distribution of distances (Random Distance) or directions (Random Direction) or were derived from the best model for distance (Modeled Distance) and transition probabilities for direction (Modeled Direction). The Modeled Distance-Modeled Direction model best described bumble bee movement. For leafcutting bees, a Random Distance-Random Direction model was favored. If we assume the lower sample sizes provided lower power to discriminate among models, the Modeled Distance-Modeled Direction likely describes honey bee movement. Using these models of pollinator movement, we obtained shortest net distances traveled by leafcutting bees, followed by honey bees and last, bumble bees. Pollen dispersal curves and seed curves provided similar rankings of bee species with respect to pollen dispersal and gene flow. Rankings for leafcutting bees and honey bees were supported by gene flow data. Leafcutting bee is the recommended pollinator to limit adventitious presence in alfalfa seed production fields. This study provides a mechanistic explanation for the lower gene flow by leafcutting bees and the approach developed here can be extended to other crops and their pollinators. Linking pollinator foraging behavior to pollinator movement can guide the design of pollinator strategies to minimize gene flow and facilitate coexistence in agricultural crops.