Evolution of orchids (Ophrys) with a pseudocopulatory pollination mechanism

Flowers of the European and Mediterranean orchid genus Ophrys mimic female bees and their sex pheromones, thereby attracting males. Male bees mistake orchid flowers for females and attempt to mate with them. During this so-called pseudocopulation, pollen material is attached to, or removed from, the bee and pollination is achieved. Sex pheromones are species-specific in bees and so is their imitation by orchid flowers. Thus, every Ophrys species has only one highly specific pollinator. The formation of new orchid species, therefore, should primarily be due to changes in pollinators and an accompanying change in the odour bouquets of the flowers. This might even apply in cases where populations have remained in geographic contact (sympatric speciation). This project seeks to identify such pollinator changes by reconstructing evolutionary history using molecular markers (nuclear DNA markers). The impact of pollinators on gene flow between plant populations, and therefore also species formation, will be assessed using molecular population genetic methods. We will compare situations where different taxa can be reliably recognised based upon floral morphology. With respect to pollinators, three cases can be distinguished: (1) closely related species that have different pollinators; (2) closely related species that have identical pollinators but are separated by other means (e.g., by geography); and (3) taxa that have identical pollinators because these have been acquired independently (convergent evolution). We will be able to distinguish these cases once the exact relationships of orchid species are known. Moreover, the identification of pollinator switches during orchid evolution, and comparative analyses of odour bouquets, will allow us to develop a hypothesis on the molecular mechanisms underlying speciation.

Flowers of the European and Mediterranean orchid genus Ophrys mimic female bees and their sex pheromones, thereby attracting males. Male bees mistake orchid flowers for females and attempt to mate with them. During this so-called pseudocopulation, pollen material is attached to, or removed from, the bee and pollination is achieved. Sex pheromones are species-specific in bees and so is their imitation by orchid flowers. Thus, every Ophrys species has only one highly specific pollinator. The formation of new orchid species, therefore, should primarily be due to changes in pollinators and an accompanying change in the odour bouquets of the flowers. This might even apply in cases where populations have remained in geographic contact (sympatric speciation). This project seeks to identify such pollinator changes by reconstructing evolutionary history using molecular markers (nuclear DNA markers). The impact of pollinators on gene flow between plant populations, and therefore also species formation, will be assessed using molecular population genetic methods. We will compare situations where different taxa can be reliably recognised based upon floral morphology. With respect to pollinators, three cases can be distinguished: 1. closely related species that have different pollinators; 2. closely related species that have identical pollinators but are separated by other means (e.g., by geography); and 3. taxa that have identical pollinators because these have been acquired independently (convergent evolution). We will be able to distinguish these cases once the exact relationships of orchid species are known. Moreover, the identification of pollinator switches during orchid evolution, and comparative analyses of odour bouquets, will allow us to develop a hypothesis on the molecular mechanisms underlying speciation.