Movement of Pollinators and Their Impact on Selfing and Gene Flow in Alfalfa.

摘要

Insect pollinators are important for the seed production of vegetables and fruits and for some forage and oil crops. Little is known about their impact on selfing, gene flow and plant mating systems. Both selfing and gene flow in agriculture are affected by how pollinators forage on plants. How pollen is deposited from flower to flower throughout consecutive visits can vary among pollinators. Pollinators can affect the proportion of seeds that results from self-fertilization. Also, pollinators can mediate gene flow via pollen and therefore help move genes among fields. Alfalfa represents a good model system to contrast the impact of distinct pollinators on selfing and gene flow. This thesis examines the foraging behavior of the European honey bee, the common eastern bumble bee and the alfalfa leafcutting bee on alfalfa plants and determine their impact on selfing rate and potential for gene flow. Selfing rate estimates were higher on plants visited by leafcutting bees and honey bees relative to bumble bees. Differences among bee species on the number of sequentially visited flowers, tripping rates and their ability to remove or deposit more pollen grains during a visit to a flower can explain the differences observed in selfing rates. We also quantified the impact of these pollinators on the reproductive success via female and male functions in alfalfa. Bee species affected plant reproductive success via both female and male functions. Plants visited by bumble bees had greater female and male reproductive success relative to honey bees and leafcutting bees. Differences among bee species in their impact on plant reproductive success were linked to differences in foraging behavior. Lastly, we compared pollen deposition curves for two bee species and their potential for transgene escape. Leafcutting bees exhibited steeper pollen deposition curves, hence shorter tails relative to bumble bees. This work improves our understanding of how distinct pollinators affect selfing rate and gene flow and therefore, how pollinators affect plant mating systems and ultimately the genetic structure of plant populations. This research contributes to the development of planting strategies to help reduce transgene escape and to promote the effective coexistence across different markets.