Gene flow in Australian sexually-deceptive orchids

A project undertaken at the School of Botany & Zoology, Australian National University, and supervised by Michael Whitehead and Rod Peakall

Species of the Australian orchid genus Chiloglottis employ the intriguing pollination strategy of sexual deception in which the orchid lures the pollinator - male thynnine wasps - through chemical mimicry of the wasp’s sex pheromones. At the flower the wasps will often attempt copulation during which a load of pollen is stuck to its body for export to another orchid flower. Pollen-laden wasps will transfer the pollen package, completing pollination, when they visit a second flower.

This project focuses on a system of co-occurring and co-flowering (sympatric) closely related sexually deceptive orchids; Chiloglottis valida and the undescribed C. aff. jeansii. Recent research on these and other orchids in the genus Chiloglottis has identified the chemicals involved in pheromone mimicry. Furthermore, related but slightly different chemical variation has been shown to illicit attraction of different pollinator species. These recent discoveries lead us to predict that these two sister species have evolved as a result of pollinator-driven speciation. Furthermore, it is possible that reproductive isolation or barriers to gene flow may have arisen despite the species co-occuring when changes in floral chemical profile resulted in pollinator switching and strong pollinator-mediated selection.

Studies of gene flow are required to expand our knowledge of speciation in this system and pollinator-driven speciation more generally. By studying gene flow we hope to answer questions such as: How far can a pollinating wasp take pollen from a paternal plant? How exclusive is the orchid’s relationship with its associated pollinator? Does hybridization occur between co-occurring and co-flowering orchid taxa? Our multidisciplinary approach to the investigation of gene flow in this system employs modern molecular genetic methods such as DNA profiling and paternity analysis as well as traditional ecological methods such as pollen labeling techniques and mark-recapture of pollinators.

Further reading:

Ledford, H (2007) Plant Biology: The Flower of Seduction. Nature 445, 816-817

Schiestl FP, Peakall R, Mant JG, et al. (2003) The chemistry of sexual deception in an orchid-wasp pollination system. Science 302, 437-438.

http://www.anu.edu.au/BoZo/orchid_pollination

 

Figure 1: Chiloglottis valida, Kanangra-Boyd National Park, NSW. (Photo: M Whitehead)

Figure 2: The labellum of Chiloglottis valida with its projecting calli is highly specialized to attract wasp pollinators. (Photo: R Peakall)