Chemical mediators of pollinator specificity breakdown in dioecious Ficus deltoidea complex

Abstract

The specific interaction of fig (Ficus) and its fig wasp pollinator (Agaonidae) is sustained by the olfactory signal in combination with morphological co-adaptations. Ficus deltoidea complex is a dioecious fig tree that is regularly pollinated by the fig wasp Blastophaga spp. This complex includes 13 varieties, seven of which are native to Peninsular Malaysia. The classification relies exclusively on leaf characterisation, without considering gene flow across sympatric taxa. Additionally, it remains unexplored whether different varieties support distinct fig wasp pollinators, or to what extent the floral scents emitted by receptive phase figs of these varieties differ. An experiment was conducted to determine the host specificity of Blastophaga sp. from var. trengganuensis in the germplasm of UniSZA by placing a donor male tree from var. trengganuensis surrounded by other varieties. To see the correlation between the varieties entered by the fig wasps and the volatile odour compound (VOC) releases from the receptive figs, a headspace solid-phase microextraction and gas chromatography–mass spectrometry analysis were used. The breakdown of one-to-one specificity in fig and fig wasp mutualism occurs when Blastophaga sp. from var. trengganuensis enters another variety (var. kunstleri) apart from its own variety. Monoterpenes, sesquiterpenes, and aliphatic compounds were detected in the odours of five sympatric fig varieties of F. deltoidea with varying compositions. Multivariate data analysis using PLS revealed the existence of three distinct groups based on differences in VOC content. Females of both var. kunstleri and var. trengganuensis were clustered together, with 12 compounds identified as potentially correlated with the number of fig wasps that entered. Our findings imply that pollinator specificity in figs was potentially mediated by chemical signals in the fig odour where the overlapping of compounds between two varieties caused the pollinators from one variety to reach their non-host plants. Pollinator sharing between two varieties revealed the breakdown of pollinator specificity in var. trengganuensis, showing gene flow is happening in the closely related trees that differ in appearance.