FLORAL ISOLATION IS THE MAIN REPRODUCTIVE BARRIER AMONG CLOSELY RELATED SEXUALLY DECEPTIVE ORCHIDS
Article first published online: 9 JUN 2011
© 2011 The Author(s).
Volume 65, Issue 9, pages 2606–2620, September 2011
How to Cite
Xu, S., Schlüter, P. M., Scopece, G., Breitkopf, H., Gross, K., Cozzolino, S. and Schiestl, F. P. (2011), FLORAL ISOLATION IS THE MAIN REPRODUCTIVE BARRIER AMONG CLOSELY RELATED SEXUALLY DECEPTIVE ORCHIDS. Evolution, 65: 2606–2620. doi: 10.1111/j.1558-5646.2011.01323.x
- Issue published online: 1 SEP 2011
- Article first published online: 9 JUN 2011
- Accepted manuscript online: 15 APR 2011 10:53AM EST
- Received November 30 2010, Accepted March 31 2011
- Floral odor;
- reproductive isolation;
- sexually deceptive orchids;
Floral isolation is an important component of pollinator-driven speciation. However, up to now, only a few studies have quantified its strength and relative contribution to total reproductive isolation. In this study, we quantified floral isolation among three closely related, sympatric orchid species of the genus Ophrys by directly tracking pollen flow. Ophrys orchids mimic their pollinators’ mating signals, and are pollinated by male insects during mating attempts. This pollination system, called sexual deception, is usually highly specific. However, whether pollinator specialization also conveys floral isolation is currently under debate. In this study, we found strong floral isolation: among 46 tracked pollen transfers in two flowering seasons, all occurred within species. Accounting for observation error rate, we estimated a floral isolation index ≥0.98 among each pair of species. Hand pollination experiments suggested that postpollination barriers were effectively absent among our study species. Genetic analysis based on AFLP markers showed a clear species clustering and very few F1 hybrids in natural populations, providing independent evidence that strong floral isolation prevents significant interspecies gene flow. Our results provide the first direct evidence that floral isolation acts as the main reproductive barrier among closely related plant species with specialized pollination.