The mechanics of nectar offloading in the bumblebee Bombus terrestris and implications for optimal concentrations during nectar foraging.
Journal of the Royal Society, Interface
Royal Society Publishing
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Pattrick, J. G., Symington, H., Federle, W., & Glover, B. (2020). The mechanics of nectar offloading in the bumblebee Bombus terrestris and implications for optimal concentrations during nectar foraging.. Journal of the Royal Society, Interface, 17 (162), 20190632. https://doi.org/10.1098/rsif.2019.0632
Nectar is a common reward provided by plants for pollinators. More concentrated nectar is more rewarding, but also more viscous, and hence more time-consuming to drink. Consequently, theory predicts an optimum concentration for maximising energy uptake rate, dependent on the mechanics of feeding. For social pollinators such as bumblebees, another important but little-studied aspect of foraging is nectar offloading upon return to the nest. Studying the bumblebee Bombus terrestris, we found that the relationship between viscosity (μ) and volumetric transfer rates (Q) of sucrose solutions differed between drinking and offloading. For drinking, Q ∝ μ^-0.180, in good agreement with previous work. Although offloading was quicker than drinking, offloading rate decreased faster with viscosity, with Q ∝ μ^-0.502; consistent with constraints imposed by fluid flow through a tube. The difference in mechanics between drinking and offloading nectar leads to a conflict in the optimum concentration for maximising energy transfer rates. Building a model of foraging energetics, we show that including offloading lowers the maximum rate of energy return to the nest and reduces the concentration which maximises this rate by around 3 %. Using our model we show that published values of preferred nectar sugar concentrations suggest that bumblebees maximise the overall energy return rather than the instantaneous energy uptake during drinking.
This work was supported by a Biotechnology and Biological Sciences Research Council PhD Studentship under grant BB/J014540/1 to J.G.P.
External DOI: https://doi.org/10.1098/rsif.2019.0632
This record's URL: https://www.repository.cam.ac.uk/handle/1810/300293
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