Pollinator-driven speciation in sexually deceptive orchids of the genus ophrys

Abstract

Ophrys orchids mimic females of their pollinator species to attract male insects for pollination. Reproductive isolation is based on the specific attraction of males of usually a single pollinator species, mostly bees, by mimicking the female species-specific sex-pheromone. Sexually deceptive orchids are ideal candidates for studies of sympatric speciation, because key adaptive traits such as the pollinator-attracting scent are associated with their reproductive success and with premating isolation. We have investigated processes of ecological speciation by using behavioural experiments and chemical, electrophysiological and population-genetic analyses. We show that minor changes in floral odour bouquets might be the driving force for pollinator shifts and speciation events. New pollinators act as an isolation barrier towards other sympatrically occurring species. Hybridisation occurs because of similar odour bouquets of species and the overlap of flowering periods. Hybrid speciation can also lead to the displacement of species by the hybrid population, if its reproductive success is higher than that in the parental species.