PARENT SESSION
Poster Session #46: Seed Production, Recruitment, and Pollination.
Friday, August 10, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Pollen dispersal by bumble bees and butterflies visiting Brassica napus: implications for plant mating.

Williams, Neal¹, Harder, Lawrence¹, ¹

ABSTRACT- Pollen dispersal by insects underlies mating patterns in many plant species, critically linking pollinators and pollen movement to floral evolution and seed yield. We measured pollen dispersal for two different pollinator species, bumble bees (Bombus melanopygus) and pierid butterflies (Pieris rapae), visiting experimental arrays of Brassica napus. We tracked pollen dispersed from a focal donor plant following visitation by a single pollinator. Use of a transgenic plant as the donor allowed us to distinguish its pollen without affecting the dispersal process. Pollen grains from these transgenic plants turn blue with specific staining. During 30 dispersal trials for each pollinator species, we also characterized visitation behavior at flowers and plants. Dispersal and behavioral data were combined to compare differences in plant mating patterns caused by each pollinator species. Pollen deposition curves, estimated with maximum likelihood, exhibited a characteristic leptokurtic shape for both pollinators. Over 80% of donor pollen was deposited on the first five recipient flowers. Despite similarly shaped deposition curves, bumble bees dispersed three times more pollen from the donor per visit than did butterflies. Differences between pollinator species in the number of flowers visited per plant and the variation in grains deposited per flower significantly affected the number of plants receiving donor pollen and their "distances" from the donor. Bees dispersed pollen to more recipients (mean=5.2±0.5; 3.1±0.4 for butterflies), but butterflies dispersed pollen to equally distant recipients.

KEY WORDS: pollen dispersal, transgenic plant, butterfly, bumble bee