Fishbein, Mark , O'Quinn, Robin , Slotta, Tracy , Raguso, Robert A. .
Patterns of Floral Scent Variation in an Asclepias Hybrid Zone.
FLORAL odor acts as a powerful attractant for animal pollinators and may also play a critical role in pollinator-mediated hybridization. Here we characterize scent chemistries for Asclepias exaltata, A. syriaca and their putative hybrid offspring using combined gas chromatography-mass spectrometry. We found striking differences in the scent compositions and emission rates of the two parental species. Asclepias syriaca has a strong, pleasing floral scent with a complex spectrum of compounds including several apparently novel floral odors. In contrast, A. exaltata has a weak, fairly unpleasant scent composed of fewer compounds. Hybrid scents are more similar in complexity and emission rate to A. syriaca than A. exaltata. Hybrid individuals have strong, sweet scents that differ from both parents by exhibiting transgressive expression for several key aromatic compounds found in A. syriaca, but not A. exaltata. Emission rates are consistent between night and day for all taxa, but higher overall for A. syriaca and hybrids than for A. exaltata. We also found variation in floral organ-specific patterning, at the level of biosynthetic pathways for all taxa. We dissected flowers into three parts: petals, coronas and gynostegia; and classified scent compounds into three major categories: aromatics, monoterpenoids and sesqueterpenoids. Aromatic compounds are localized to the gynostegium and corona in A. exaltata, but are found in all three floral parts of A. syriaca and hybrids. Sesqueterpenoids are plentiful in A. exaltata, are largely absent from A. syriaca, and have intermediate expression in hybrids. Sesqueterpenoids are expressed in all three parts of A. exaltata, but only the gynostegium and corona of hybrids. Levels of monoterpenoid expression are uniformly high across all floral parts and all taxa. Similarity in scent composition and emission rates between A. syriaca and hybrids suggest asymmetrical introgression and/or that backcrosses with A. syriaca may be more prevalent in this system.
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1 - Portland State University, Biology Department, Po Box 751, Portland, Oregon, 97207-0751, USA
2 - United States Department of Agriculture-Agricultural Research Service, Plant Science Research Unit, 1605 Albrecht Blvd., Fargo, North Dakota, 58105-5674, USA
3 - University of South Carolina, Department of Biological Sciences, Coker Life Sciences Building, 700 Sumter St., Columbia, South Carolina, 29208, USA
Presentation Type: Oral Paper:Papers for Topics
Date: Monday, July 31st, 2006
Time: 4:15 PM