The pollination and breeding system of Dipterocarpus obtusifolius (Dipterocarpaceae) in dry deciduous forests of Thailand

Abstract

The pollination biology of Dipterocarpus obtusifolius (Teijsm.), an obligately insect-pollinated dry deciduous dipterocarp tree, is described. For the first time, the pollinators of a Dipterocarpus species are identified, and they are found to be large Lepidoptera, a new pollination syndrome for this tree family. D. obtusifolius produces relatively few large, pink, pendulous flowers that emit a strong fragrance upon opening. Flowers open at dusk and remain open for 24–36h. Nectar secretion occurs at flower opening and continues through the next day. Pollen is maximally available at night but much pollen remains available to daytime visitors. The stigma is spatially separated from the anthers but pollen presentation and stigma receptivity occur simultaneously. In artificial pollination experiments there was intense selection pressure, through abscission of young fruit, in favour of outcrossing. Pollination did not occur in the absence of insect vectors. Large moths (Sphingidae and Noctuidae) are the primary pollination vectors at night and account for 60% of pollen transfer. Butterflies (primarily Pieridae and Papilionidae) pollinate flowers during the day. It is likely that birds pollinate a small proportion of flowers. The pollination syndrome and breeding system of this species is discussed in relation to its biogeography.