PARENT SESSION
Oral Session #101: Plant-Animal Interactions.
Presiding: S. Faeth
Friday, August 9. 9:00 AM to 12:00 PM. Coconino Meeting Room, TCC.

Toxic nectar mediates tradeoffs between pollination and nectar robbing in Gelsemium sempervirens.

Adler, Lynn^*,1, Irwin, Rebecca², ¹ Virginia Polytechnic Institute and State University, Blacksburg, VA² University of Georgia, Athens, GA

ABSTRACT- Individuals face simultaneous direct and indirect interactions with mutualists and antagonists, yet our understanding of the relative importance of these competing pressures is still rudimentary. For example, flowering plants may face the dilemma of attracting pollinators while discouraging floral enemies, such as nectar robbers. We determined how toxic nectar, a ubiquitous but poorly understood floral trait, influences interactions with both nectar robbers and pollinators by adding artificial nectar with and without the alkaloid gelsemine to flowers of Gelsemium sempervirens, a perennial vine with documented gelsemine in its nectar. We found that alkaloids in nectar significantly reduced the number of flowers probed per visit by both pollinators and nectar robbers, and the time spent per flower by robbers. Floral visitation by nectar-robbing carpenter bees was reduced 37% by toxic nectar compared to control nectar, but floral visitation by pollinating bumblebees was reduced nearly 75%. Toxic nectar may therefore constitute a cost to plants in terms of reduced pollination as well as a benefit in terms of reduced nectar robbing. Thus, we must consider the role of antagonists such as nectar robbers and herbivores, as well as mutualists such as pollinators, in shaping the evolution of floral traits in plants.

KEY WORDS: mutualism, floral evolution, species interactions, alkaloids