Do mating system and pollinator preferences vary with habitat for Leptosiphon bicolor and L androsaceus (Polemoniaceae)?

Mating system differences in two closely related species of Leptosiphon may vary with habitat and moisture availability. L. bicolor and L. androsaceous occur in Henry Coe State Park, California where multiple populations have been observed along a naturally occurring moisture availability gradient. Populations found on the western side of the park receive about twice as much precipitation as those populations found on the eastern side.  Both species of Leptosiphon are insect-pollinated but may also self-fertilize. Our objective was to examine how the contribution of pollinators to reproduction varies with habitat for these two species of Leptosiphon. We measured corolla diameter and counted pollen grains on stigmas of open-pollinated plants to observe pollinator preferences for floral size. We also conducted a pollinator exclusion and hand-pollination experiment to assess the dependence of reproduction on pollinators. L. bicolor had 15% larger corolla diameter in the western population than in the eastern.  It had similar seed set in caged and open-pollinated plants in both habitats.  Hand pollination did not increase seed set for L. bicolor.  Therefore, this species is predominantly self-pollinating. L. androsaceus had 25% larger corollas in the western populations than in the eastern.  Pollinators preferentially visited the larger flowers of this species.  Furthermore, outcrossing was more frequent in the western habitat than in the east.  These results show that pollinators have little influence on reproduction of L. bicolor. However, the role of pollinators on seed set for L. androsaceus varies with habitat.