The role of pollination drops in animal pollination in the Mediterranean gymnosperm Ephedra fragilis (Gnetales)

Abstract

The pollination drop (PD) is a sweet secretion produced by female cones of many gymnosperms whose main function is associated with the capture and transport of pollen to the nucellar surface of the ovule. Due to its high sugar content, PDs appear to be highly suitable for the attraction of animals that might act as potential pollinators for gymnosperms. In the present study, we evaluated the attraction of animals to female and male PDs (sugar-rich rewards) in plants of the Mediterranean shrub Ephedra fragilis in addition to their contribution to plant fitness. Animal exclusion experiments were conducted in Sa Dragonera Islet Natural Park (Western Mediterranean, Spain). In addition, a link between PD investment (PD concentration) and plant fitness was evaluated on plants of E. fragilis. Lizards and insects were the principal visitors to PDs offered by E. fragilis plants. Animals effectively contributed to plant fitness. Nevertheless, the fitness contribution was not as elevated as the contribution from wind pollination (~30 vs. 70 %, respectively). Increased plant investment on PDs significantly elevated fitness in plants of E. fragilis. The present study provides evidence that E. fragilis relies primarily on wind pollination, with pollination and fitness being supplemented by animal visitation. Additionally, besides its main role as pollen capture and germination, PDs act as a pollinator reward that benefits plant reproduction.