Abstract
Floral stickiness is a rare trait with unknown function, but it is common in the mega-diverse Cape genus Erica (Ericaceae). This study investigated the role of stickiness measured as adhesive strength in Erica as protection against nectar robbing and its correlation with floral traits. We compared the incidence of nectar robbing in flowers of the same species with or without experimentally added stickiness, and amongst communities of co-occurring species with flowers differing in stickiness. Additionally, we tested the relationship between stickiness and pollination syndrome, corolla shape, corolla length and sepal-corolla ratio across the whole genus. Stickiness was correlated with lower floral damage rates within and between species, indicating it functions as an anti-nectar robbing trait. Across the genus Erica, stickiness is most strongly correlated with bird and long-proboscid fly pollination, presumably because of their larger nectar rewards. Stickiness was also correlated with floral traits that are often associated with high risk of being damaged by nectar robbers: narrow-mouthed corollas, long corollas and shorter sepals. These results show that corolla stickiness defends Erica flowers against nectar robbing and thereby potentially improves fitness.
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Acknowledgements
We are very grateful to all the landowners who permitted us to conduct fieldwork on their land, particularly to Vogelgat Private Nature Reserve and Giorgio Lombardi, Thys de Villiers, South African National Parks and Cape Nature. We thank Felix Herzog for advice on how to measure stickiness. We also wish to thank Betty Ann Illing for providing accommodation in Hermanus.
Funding
This study was funded by the South African National Research Foundation (Grant number: MND190724458797), the UCT Science Faculty Research Committee and DST-NRF Centre of Excellence at the FitzPatrick Institute of African Ornithology.
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The idea for this study was first conceived by SM. All authors contributed to the study design. Material preparation, data collection and analysis were performed by SM and AC. The first draft of the manuscript was written by SM and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
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McCarren, S., Coetzee, A. & Midgley, J. Corolla stickiness prevents nectar robbing in Erica. J Plant Res 134, 963–970 (2021). https://doi.org/10.1007/s10265-021-01299-z
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DOI: https://doi.org/10.1007/s10265-021-01299-z