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

Attracting 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 specific pollinators are diverse and unknown in many pollination interactions. We surveyed pollinators on three sympatric Aristolochia species (A. clematitis, A. pistolochia and A. rotunda) pollinated by Diptera to investigate if specific pollination occurs. To decipher if specific pollination may be mediated by different floral odours, we characterized the volatile organic compounds (VOCs) emitted by flowers and highlighted those VOCs electrophysiologically detected by pollinators in A. rotunda and A. pistolochia. Among the most abundant pollinators, Forcipomyia monilicornis was a specific pollinator of A. pistolochia while two Dasyhelea species were specific pollinators of A. clematitis. Forcipomyia aristolochiae and T. ruficeps were non-specific pollinators of A. rotunda, although they were more frequently found in A. rotunda flowers. 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.