PARENT SESSION
Oral Session #31: Plant Reproductive Ecology, Pollination, and Dispersal. Presiding: J. Karron.
Tuesday, August 7, 2001. 1:00 PM to 5:00 PM. Hall of Ideas L&M.

The consequences of inflorescence architecture for bumble bee behaviour and plant mating.

Jordan, Crispin¹, Harder, Lawrence¹, ¹

ABSTRACT- The floral displays of angiosperms vary greatly in size, flower design, and flower arrangement (inflorescence architecture), presumably reflecting adaptation to different pollination environments. However, the functional significance of inflorescence architecture remains poorly understood. We conducted an experiment that examined the foraging of three species of bumble bees on three types of artificial inflorescences (raceme, umbel, and panicle). We then simulated pollination based on the observed behaviour to assess differences in mating environments among architectures. The experiment and simulations yielded two classes of results. First, architecture weakly influenced the number of flowers visited by bees; bees visited more flowers on umbels than panicles. This weak effect of architecture on visitation yielded small, but significant, effects on mating when all flowers were simultaneously hermaphroditic. Second, architecture strongly affected the consistency of foraging paths among flowers (raceme > panicle > umbel). Architecture's influence on foraging paths determined the variation among flower positions within inflorescences in their contributions to mating; selfing-rates and pollen export differed most among flower positions in racemes, and did not differ within umbels. Additionally, the influence of architecture on foraging consistency greatly influenced mating when inflorescences segregated sex functions. These effects bear diverse consequences for the evolution of inflorescence architecture, flower design and plant mating.

KEY WORDS: pollination, inflorescence, architecture, behaviour