Specificity of the signal emitted by figs to attract their pollinating wasps: Comparison of volatile organic compounds emitted by receptive syconia of Ficus sur and F. sycomorus in Southern Africa

Abstract

Volatile organic compounds (VOCs) appear to be critical for mediating the extreme specificity of the obligatory mutualisms between Ficus species (Moraceae) and their pollinating wasps (Hymenoptera, Chalcidoidea, Agaonidae). In the present study, we characterized the blend of VOCs emitted by receptive syconia of two closely related fig species F. sur and F. sycomorus. Headspace samples were collected, respectively, at three and four localities per species in South Africa and Swaziland, including one locality where both species were present, and were analyzed by gas chromatography–mass spectrometry (GC–MS) using a sensitive direct thermal desorption method. A total of 56 compounds were detected, most of which were terpenoids. Some of the major VOCs emitted by receptive figs are shared by both species. However, the relative proportions of these compounds in the total blend are different between F. sur and F. sycomorus. Multivariate analysis revealed a significant difference between the volatile profiles of the two species. These results support the hypothesis that the chemical messages emitted by figs are species-specific.