Evidence for beetle pollination in the African grassland sugarbushes (Protea: Proteaceae) |
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Authors: | Sandy-Lynn Steenhuisen Steven D Johnson |
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Institution: | (1) School of Life Sciences, University of KwaZulu-Natal, P/Bag X01, Scottsville, 3209, South Africa |
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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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