Ambophily in Olea ferruginea: a transitional state in the pollination syndrome

Abstract

A number of plants species believed to be wind pollinated (anemophilous) are actually pollinated both by wind as well as insects (ambophily) because all the traits of the two pollination modes have not evolved simultaneously. Comparatively few angiosperms exhibit ambophily and the significance of such a mechanism is not fully understood. During the present investigation, ambophily was studied in Olea ferruginea, over a period of three years. It is an andromonoecious and out-crossing tree species of the olive complex. The species is predominately pollinated by wind because it shows fruit set even when the insect pollinators were excluded. Moreover, a substantial amount of pollen was observed on the body parts of insect visitors and, comparatively, fruit set was enhanced in open-pollinated flowers receiving insect visitors. Floral structure of O. ferruginea displays floral traits favoring both wind and insect pollination. Furthermore, the flowers of this species were found to be visited by 20 insect species classified under three orders with Diptera and Hymenoptera being the leading pollen foragers. The results of linear regression of the hanging slide experiment showed that the dispersal of pollen grains decreased significantly with increasing distance from the canopy and the pollen density increased significantly with an increase in insect activity. The present work provides an insight to understand the ecological and evolutionary adaptations and consequences of spatio-temporal variation in plant – pollinator interactions. It is, therefore, useful for addressing both basic and applied questions in community structure and function including the evolution of floral traits, reproductive assurance, and the development of optimal conservation strategies.