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Scent variation and hybridization cause the displacement of a sexually deceptive orchid species¹

² Institute for Experimental Ecology, University of Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany ³ Department of Systematic and Evolutionary Botany, University of Vienna, Rennweg 14, 1030 Vienna, Austria ⁴ Department of Evolutionary Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria ⁵ Institute for Human Genetics, University of Ulm, Albert-Einstein-Allee, 11 89069 Ulm, Germany

ABSTRACT

In the sexually deceptive orchid genus Ophrys, reproductive isolation is based on the specific attraction of males of a single pollinator species, mostly bees, by mimicking the female sex pheromone of this species. Changes in the floral odor can lead to hybridization, introgression, and possibly speciation. We investigated hybrid swarms of O. lupercalis and O. iricolor on Sardinia using behavioral, electrophysiological (GC-EAD), chemical, morphological, and genetic methods (AFLPs). In behavioral experiments, approximately 20% of the flowers from both species and hybrids were attractive to the "wrong" or both pollinator species. Analysis of the EAD-active hydrocarbons in the floral odor showed an overlap in the two species, whereby hybrid individuals could not be separated from O. iricolor. The genetic analysis confirmed the hybridization of the species. Plants of O. iricolor and hybrids are genetically indistinguishable and form an O. iricolor x lupercalis hybrid population. Remaining plants of O. lupercalis will possibly be displaced by the O. iricolor x lupercalis hybrid population in the future. Our study showed that in deceptive orchids, variation in the pollinator attracting cues, in this case, scent, can be the first step for speciation and at the same time cause the displacement of a species.

Key Words: AFLP • GC-EAD • hybridization • Ophrys, Orchidaceae • pollination • Sardinia • sexual deception

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