Understanding the basis of pollinator selectivity in sexually dimorphic Fragaria virginiana

Abstract

Pollinators of gender dimorphic (e.g., gynodioecious or dioecious) species often show a preference for hermaphrodite or male flowers over conspecific females, and such pollinator selectivity can have implications for the evolution of sexual dimorphism. However, because the sex morphs differ in several floral features, it is not readily apparent which specific traits generate differential pollinator service. In this study, we sought to understand the basis of pollinator preferences for hermaphrodites to females of gynodioecious Fragaria virginiana. We extend a previous study that revealed that lack of pollen‐filled anthers and shorter petals were not solely responsible for small bee and fly discrimination against females, by investigating the roles of other morphological features, reward characters, and floral context in bringing about pollinator discrimination. Using floral manipulations we revealed that small bees preferentially visit flowers with wide petals, more nectar, intact stamens, as well as flowers located in hermaphrodite‐dominated patches. Specifically, bees were able to remotely detect nectar presence. In addition, bees were attracted to both the anther sac and the filament regions of the stamen, indicating that not only anthers, but also filaments may function as visual or olfactory cues to pollen reward. Furthermore, pollinator preference for flowers in hermaphrodite‐dominated patches serves to intensify their discrimination against female flowers which occur predominantly in female‐dominated patches. For the most part, preferences of flies mirrored those of the bees with the exception that flies also showed a significant preference for flowers held high over those held closer to the ground. These results indicate that a suite of character differences contributes to pollinators’ preferences for hermaphrodite to female flowers. Furthermore, they suggest pollinators could mediate selection on both floral morphology and reward in this species.