Pollinator visitation and female reproductive success in two floral color morphs of Ipomoea aquatica (Convolvulaceae)

Abstract

© 2020, Springer-Verlag GmbH Austria, part of Springer Nature. Differences in floral morphology are often hypothesized to stem from selection by different pollinators. Thus, the presence of multiple floral color morphs within a species might indicate visitation by different pollinator species. To test this prediction, we examined Ipomoea aquatica Forssk., a morning glory species with a “white” morph (all-white flowers) and a “purple” morph (white corolla lobes with purple corolla tubes). We studied this species in Nong Khai, Thailand, where some populations are monomorphic for a single color and others are polymorphic. We compared (a) animal visitation rates to each morph; (b) visitor and pollinator community composition at each morph; and (c) the female reproduction of each morph. Visitation rates were obtained from camcorder footage and used to analyze community composition. Female reproduction was assessed from a pollination experiment with five treatments (open, open emasculation, hand-cross, hand-self, and closed). We found that the main pollinators (bees and butterflies) visited both morphs, and that overall insect community composition to the two floral colors did not differ significantly. Moreover, we found that I. aquatica is capable of spontaneous autogamy but still benefits from pollinators, as flowers in the closed treatment set significantly fewer seeds than flowers in the open and hand cross-pollinated treatments. When comparing female reproduction between morphs, we did not find significant differences for either fruit set or seed set. These findings suggest that floral visitors interact with the two morphs similarly, and that the high-reproductive success experienced by both colors may help maintain the polymorphism in nature.