Abstract
Active pollination, although rare, has been documented in a few pollination mutualisms. Such behaviour can only evolve if it benefits the pollinator in some way. The wasps that pollinate Ficus inflorescences can be active or passive pollinators. They lay their eggs in fig flowers, so that a proportion of flowers will host a wasp larva instead of a seed. We show in an actively pollinated monoecious fig that lack of pollination does not induce fig abortion or affect wasp offspring size but results in smaller numbers of offspring. Hence, conversely to other active pollination systems, seed formation is not obligatory to sustain developing pollinator larvae; however there is a direct fitness cost to active pollinators not to pollinate. We then compared the locations of eggs and fertilised flowers of three actively pollinated Ficus species and one passively pollinated species. We found that more flowers containing wasp eggs were fertilised in the actively pollinated species relative to those of the passively pollinated one. These results along with comparison with similar studies on dioecious figs, support the hypothesis that active pollination has evolved in fig wasps to ensure that more flowers containing wasp eggs are fertilised as this may increase the chances of successful gall development. The stigmatic platform characterising actively pollinated figs is probably an adaptation to increase pollen dispersion within the fig.
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Acknowledgements
This research was partly supported by a Brunei Shell Environmental Studies Fellowship and a CNRS and NRF combined s & t grant. We are grateful to Dr D. Edwards and to the Biology department staff at Universiti Brunei Darussalam for their help. We also acknowledge the Director of the Brunei Museum and the Forestry Department for allowing us to export specimens. Many thanks to Jaco Greeff and Simon van Noort for their help in finding and identifying fig trees in the field. We thank C. Brouat, J. Greeff, D. McKey, J. Pienaar and J. Shykoff for advice on earlier versions of this manuscript.
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Jousselin, E., Hossaert-McKey, M., Herre, E.A. et al. Why do fig wasps actively pollinate monoecious figs?. Oecologia 134, 381–387 (2003). https://doi.org/10.1007/s00442-002-1116-0
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DOI: https://doi.org/10.1007/s00442-002-1116-0