Pollinator specificity among three co-flowering Mediterranean Aristolochia species pollinated by Diptera

Abstract

Attracting species-specific pollinators can be favoured by natural selection to avoid reproductive interference between sympatric plant species. However, the ways in which fine differences in floral traits lead to the attraction of species-specific pollinators are diverse and unknown in most pollination interactions. We surveyed pollinators on three Aristolochia species that can occur in pairs in sympatry (A. clematitis-A. rotunda and A. pistolochia-A. rotunda) and are pollinated by Ceratopogonidae and Chloropidae (Diptera), to investigate the extent to which pollinator assemblages differ among plant species. To assess whether specificity in pollinator assemblages may be mediated by differences in floral odour composition, we characterised the volatile organic compounds (VOCs) emitted by receptive flowers and highlighted those VOCs electrophysiologically detected by pollinators of A. rotunda and A. pistolochia. Among the most abundant pollinators, females of Forcipomyia monilicornis were specific pollinators of A. pistolochia while males and females of two Dasyhelea species were specific pollinators of A. clematitis. Females of Forcipomyia aristolochiae and of Trachysiphonella ruficeps were the main pollinators in A. rotunda but also pollinated the other two species. The floral odours of A. rotunda and A. pistolochia differed significantly from each other and elicited specific electrophysiological responses in their respective pollinators. Although several pollinator species visit more than one Aristolochia species, those pollinators are preferentially found in one Aristolochia species. Selective attraction is likely mediated by specific VOCs.