Linking pollinator behavior to selfing rate and pollen discounting for three distinct pollinators of alfalfa

Selfing, results in an increase in homozygosity and therefore a decrease in genetic diversity within populations.  This process occurs when pollen from a plant is transferred to the stigma on the same plant.  Selfing can negatively impact plant fitness when associated with inbreeding depression.  How pollinators move in space and how they deposit pollen on consecutive flowers while foraging can influence selfing rate. When selfing rate is high, and pollen discounting occurs, the outcross mating success of a plant decreases. Differences among pollinators in foraging behavior and pollen deposition patterns can affect the selfing rate.  We compared the pollen transfer dynamics among three pollinators: bumblebees, honeybees and leafcutters bees. Selfing rate was measure on an alfalfa field setting pollinated with the three distinct pollinators. We genotype seeds and maternal tissue using 16 SSR markers. Field wide selfing rate was estimated at 27%, which is too high for a plant that relies on outcross pollination.  To compare the impact and pollen transfer dynamics among the three pollinators on selfing rate in alfalfa, we conducted individual experiments for each pollinator type in a greenhouse with cloned plants from the field. Studying the movement of distinct bees in field and greenhouse settings will allow us to determine the factors that affect the movement of these pollinators and how they affects selfing. The foraging behaviors of the bees on alfalfa were recorded for 20 foraging bouts per pollinator type. This study will shed light on how distinct pollinators affect plant mating system and the genetic structure of plant populations.