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Evidence for beetle pollination in the African grassland sugarbushes (Protea: Proteaceae)

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Abstract

Most lineages in the African genus Protea consist of species with large unscented flowers pollinated principally by birds, and several of these lineages also show evidence of shifts to rodent pollination, associated with concealed yeasty-scented flowerheads. In this study we investigated the hypothesis that brightly coloured and fruity-scented flowerheads of four Protea species (P. caffra, P. simplex, P. dracomontana and P. welwitschii) represent a novel shift from bird to insect pollination in a grassland lineage in the genus. These species are visited by a wide range of insects, but cetoniine beetles were found to be the most important pollinators because of their abundance, size and relatively pure pollen loads. Three of the four putatively insect-pollinated Protea species have flowers presented at ground level, and experiments showed that cetoniine beetles preferred inflorescences at ground level to those artificially elevated to the height of shrubs and small trees. Relative to insects, birds were infrequent visitors to all of the study species. The nectar of all the study species contained xylose, as documented previously in bird- and rodent-pollinated Protea species, suggesting that this is a phylogenetically conserved trait. However, the very low concentration of nectar (ca. 8%), short nectar-stigma distance and the fruity scent of florets appear to be traits that are associated with specialisation for pollination by cetoniine beetles.

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Acknowledgments

We are grateful to the Mondi forestry company for permission to work in the Mount Gilboa Estate; KZN Wildlife for permission to work in KZN protected areas (project no. NA/20094/02); the National Research Foundation for funding the study; Prof. Dennis Brothers, Ray Miller, Serban Proches and Adam Shuttleworth for insect identifications; Ben-Erik Van Wyk, Isa Bertling and Samson Tesfay for helping with the HPLC sugar analysis; UKZN Centre for Microscopy; Paul Neal for helping with rodent trapping; and Anna Hargreaves, Dave Thompson, Paulo Massinga, Craig Peter, Justin Hart, Caroline Bell, Gail Potgieter, Katherine Johnston and the Steenhuisen family for field assistance; and Jeannette Valerie Steenhuisen, Natalie Swanepoel and Rushda Khan for assistance with counting pollen.

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  1. School of Life Sciences, University of KwaZulu-Natal, P/Bag X01, Scottsville, 3209, South Africa

    Sandy-Lynn Steenhuisen & Steven D. Johnson

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  1. Sandy-Lynn Steenhuisen
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  2. Steven D. Johnson
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Correspondence to Sandy-Lynn Steenhuisen.

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Steenhuisen, SL., Johnson, S.D. Evidence for beetle pollination in the African grassland sugarbushes (Protea: Proteaceae). Plant Syst Evol 298, 857–869 (2012). https://doi.org/10.1007/s00606-012-0589-5

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  • DOI: https://doi.org/10.1007/s00606-012-0589-5

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