Corolla morphology facilitates both autogamy and bumblebee pollination in Mimulus guttatus

Abstract

The showy corolla of Mimulus guttatus is generally considered an adaptation to attract pollinators. We use phenotypic manipulations to demonstrate that corolla morphology plays a critical mechanical role in both outcrossing and self-fertilization. In the absence of pollinators, the lower portion of the corolla facilitates autogamy by retaining pollen released from the anthers. A substantial portion of self-fertilization seems to occur late in the floral life span as the stigma contacts the corolla. When pollinators are present, the corolla facilitates outcrossing before, during, and after insect visitation. A large fraction of cross-pollen is actually captured by the corolla and not by the stigma. This "indirect" pathway for pollen reception suggests that a large fraction of cross-pollination in M. guttatus actually occurs long after a pollinator departs from a flower.