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How aggressive ant-guards assist seed-set in Acacia flowers

Nature volume 388, pages 165–167 (1997)Cite this article

Abstract

The phenomenon of ant-guarding on Acacia trees is probably the best known case of a mutualism between plants and animals, the ants conferring biotic defence against herbivores and perhaps against encroaching vegetation1,2,3. However, as with many defence mutualisms, sometimes the interests of the plant and its defender conflict: for example, when they are in flower the Acacia trees require the presence and service of other insects to effect cross-pollination. How is pollinator access achieved in the face of aggressive ant-guards? Here we report that ants are deterred from young flowers at the crucial stage of dehiscence, allowing bees and other pollinators to visit and transfer pollen. This deterrence appears to be a response to a volatile chemical signal from young flowers, perhaps from the pollen itself. Ants patrol the young (undehisced) buds, and also return to the flowers after dehiscence, protecting the fertilized ovules and developing seeds. The outcome is a directly improved seed-set in the presence of ants (rather than an indirect extra reproductive resource allocation due to decreased defoliation4,5,6).

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Figure 1
Figure 2
Figure 3: Effects of ant-guard abundance on seed-set.

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Acknowledgements

We thank D. Mafunde at Mkomazi Research Station for expert field assistance; T. Morgan and N. McWilliam for invaluable logistic back-up; and M. Ritchie and J. Graves for statistical advice. We thank the Royal Geographical Society, the Darwin Initiative and the British Council for financial support, as part of the Mkomazi Ecological Research Programme, and the Department of Wildlife of the Tanzanian Government.

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Authors and Affiliations

  1. School of Biological & Medical Science, University of St Andrews, KY16 9TS, Fife, UK

    P. G. Willmer

  2. Department of Zoology, South Parks Road, OX1 3PS, Oxford, UK

    G. N. Stone

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  1. P. G. Willmer
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  2. G. N. Stone
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Correspondence to P. G. Willmer.

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Willmer, P., Stone, G. How aggressive ant-guards assist seed-set in Acacia flowers. Nature 388, 165–167 (1997). https://doi.org/10.1038/40610

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