Format: ORAL

Javier Valverde

Universidad de Sevilla, Seville, Spain

Populations of distylous species are composed of individuals of two floral morphs that exhibit contrasting but reciprocal spacial arrangement of sexual organs: in the short-styled morph (S-morph), stigmas are located below the anthers, while in the long-styled morph (L-morph) this arrangement is reversed. This feature predicts cross-pollination between morphs, promoted by the morphological fit of pollinators to flowers and sexual organs. However, it has been reported that the pollination process can occur more efficiently in one direction (from L- to S-morph flowers or vice versa), suggesting a sub-optimal efficiency of the pollinator assemblage. This study analyses the relationship between pollinator composition and pollination efficiency in 16 populations of a distylous species. Pollination efficiency at each population and direction was assessed by quantifying pollen deposition and pollen tube growth through epifluorescence microscopy. The data shows inter-population variation in the efficiency of pollen flow, which was explained by the composition of the pollinator assemblage. In particular, in populations with a lower proportion of visits from a beefly genus, pollen flow from L- to S-morph flowers occurred less efficiently. This result points to suboptimal pollination as a driver of asymmetrical pollen flow in distylous species and highlight the importance of pollinators in the proper functioning and probably evolutionary maintenance of distyly.