Abstract
Some plants are exclusively pollinated by an insect whose larvae feed on their seeds. The net outcome of a single visit for the plant depends on the number of ovules fertilised by the visitor, the number of eggs laid, and the number of seeds eaten by each larva. Unlike other known plant-seed eater pollinating mutualisms, the globeflower-globeflower fly mutualism (Trollius europaeus-Chiastocheta spp.) is unique in that not only females but also males visit flowers, and both sexes are potential pollinators. I analysed the relative efficiency of Chiastocheta males versus females in transporting pollen and fertilising globeflower ovules. I show that there is no sex-specific morphological adaptation or behaviour to enhance pollen collection and transportation in Chiastocheta flies, and that males contribute to pollination. However, because of their smaller body size, males transport significantly less pollen than females. Less seeds are produced after a visit from a male than after a visit from a female. A single female visit contributes to about 12% of total seed production, and a single male visit to only 5.4%. Females tend to spend more time inside the flower than males, and the number of ovules fertilised is significantly correlated with the time insects spent inside the closed corolla. The lower efficiency of ovule fertilisation by a male's single visit is compensated for by the higher rate of flower visitation by males: a flower receives about twice as many visits from males as from females during a time unit. The contribution of males to pollination is of major importance with respect to understanding the evolutionary stability of the globeflower-globeflower fly mutualism, as males satiate pollen requirement of flowers, masking the antagonistic effect of ovipositing females.
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Acknowledgements
I thank Julie Siegel, Ophélie Clet, Nicolas Champurney and Pierre Touraille for field assistance. I also thank Stéphanie Blanc-Manel, Irène Till-Bottraud and Finn Kjellberg for critical reading of the manuscript.
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Després, L. Sex and pollen: the role of males in stabilising a plant-seed eater pollinating mutualism. Oecologia 135, 60–66 (2003). https://doi.org/10.1007/s00442-003-1181-z
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DOI: https://doi.org/10.1007/s00442-003-1181-z