Comparative analysis of floral scents in four sympatric species of Serapias L. (Orchidaceae): clues on their pollination strategies

Orchid species of Mediterranean genus Serapiasoften live in sympatry, exhibit similar floral morphology,bloom in the same period and share the samepollinators. Previous studies on Serapias species haveascertained that reproductive isolation is based on prepollinationbarriers, that secretory cells and trichomes aretypically distributed on the floral labellum and that flowersproduce aliphatic compounds. In this study we compare thefloral scent composition of four widespread, co-occurringSerapias species, namely Serapias lingua, Serapias parviflora,Serapias vomeracea and Serapias cordigera. Ourgoals are to assess if differences in floral scent may act asinterspecific pre-pollination barriers and if these olfactorysignals may be involved in the pollination strategy ofSerapias. We find that all the selected species produceC20–C29 alkanes and alkenes and, in addition, havedetected the presence in S. cordigera of large amounts ofoleate and stearate ethyl ester. Our findings help to clarifythat the sympatric Serapias species have slightly differentfloral scent signatures that may account for their relevantrole as pre-pollination barriers. Therefore, the pollinationstrategy of Serapias relies not only on the tubular shape oftheir floral corolla but also on the production of olfactorysignals that may lure potential pollinators and even assure asufficient degree of pollinator fidelity.