PARENT SESSION
Oral Session # 34: Plant Ecology II: Pollination and Dispersal.
Presiding: A McEuen
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 202.
Targeting pollinators and evading herbivores: Floral scent emission in two species of Cirsium.
Brown, Nina*,1, Raguso, Robert2, 1 SUNY Stony Brook, Stony Brook, NY2 University of South Carolina, Columbia, SC
ABSTRACT- Floral volatile emissions attract pollinators to reproductive structures and thus promote cross-pollination. By increasing the apparency of reproductive parts, plants face the danger of attracting floral herbivores with the same signals that they use to lure pollinators. In two species of thistle, Cirsium arvense, a dioecious, exotic invasive species, and C. repandum, a native to the southeastern United States, we have investigated the potential mechanisms by which these plants modify volatile emissions to avoid attracting detrimental insects. Using a combination of analytical chemistry and field research, we examined the variability in emissions in relation to the foraging patterns of both pollinators and herbivores, including phenological preference and diel patterns. We found that in C. arvense the peak in floral volatile emissions correlates with the peak in pollinator activity rather than temperature. In contrast, C. repandum tracks temperature rather than the diel pattern of pollinators, peaking in scent emissions at the hottest time of the day. Nighttime, the coldest time of the day, is also the low point in scent emission for both thistles. While pollination in C.arvense does not occur at night (in the population we studied), C. repandum receives nocturnal pollination, at a level equivalent to daytime intensity. In order to avoid attracting herbivores, scent should be minimized prior to and following reproductively receptive times. In C. arvense androecious plants produce more scent then gynoecious plants. In fact, the full blend is not represented in gynoecious inflorescences until florets begin to emerge. In both thistle species there is a drop in scent emissions following bud break, and both peak in scent production at full maturity. We found no potential repellent compounds prior to flowering. Following flowering, methyl salicylate increases in C. repandum suggesting a potential role as a repellent.
Key words: pollination, invasive, floral scent, herbivory