Abstract
A fundamental question in pollination ecology is how pollinators affect the evolution of different floral forms. Yet functional effects of shifts in floral form for plant and pollinator are frequently unclear. For instance, flowers that conceal pollen within tube-like anthers that are spread apart and move freely (free architecture) or are tightly joined together (joined architecture) have evolved independently across diverse plant families and are geographically widespread. Surprisingly, how their bee pollinators affect the function of both architectures remains unknown. We hypothesised that bee body size would affect foraging success and pollination differently for free and joined anther architectures. Therefore, we modified the anther architecture of a single plant species (Solanum elaeagnifolium) and used a single species of generalist bumble bee (Bombus impatiens), which varies greatly in body size. We found that on free anther architecture, larger bees were better pollinators. More pollen on their bodies was available for pollination and they deposited more pollen on stigmas. Conversely, on joined anther architecture, smaller bees were better pollinators. They collected less pollen into their pollen baskets, had more pollen on their bodies available for pollination, and deposited more pollen on stigmas. While we also found modest evidence that plants benefit more from joined versus free anther architecture, further investigation will likely reveal this also depends on pollinator traits. We discuss potential mechanisms by which pollinator size and anther architecture interact and implications for floral evolution.
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08 July 2023
A Correction to this paper has been published: https://doi.org/10.1007/s00442-023-05413-x
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Acknowledgements
We are grateful to Koppert Biologicals for bee colonies, Steve Buchmann for seeds, Abilene Mosher for greenhouse care, Jenny Burrow for assistance with pollen counting, and Russell lab members for discussion. We acknowledge this work was performed on unceded traditional territory of the Kiikaapoi, Sioux, and Osage.
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RVW, MVM, and ALR: conceived and designed the experiments. RVW, MMM, and ALR: performed the experiments and collected the data. ALR and MVM analysed the data. RVW and ALR: wrote the original draft of the manuscript; the other authors provided editorial advice.
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Communicated by Jared Gregory Ali.
The original online version of this article was revised: Error in Figure 1 legend updated.
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Wilkins, R.V., Mayberry, M.M., Vallejo-Marín, M. et al. Hold tight or loosen up? Functional consequences of a shift in anther architecture depend substantially on bee body size. Oecologia 200, 119–131 (2022). https://doi.org/10.1007/s00442-022-05246-0
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DOI: https://doi.org/10.1007/s00442-022-05246-0