EXPERIMENTAL EVALUATION OF INSECT POLLINATION VERSUS WIND POLLINATION IN LEUCADENDRON (PROTEACEAE)

摘要

Premise of research. Evolutionary transitions from insect to wind pollination are thought to have occurred many times during the angiosperm radiation. On the basis of floral features, several such transitions have been postulated for Leucadendron (Proteaceae), a dioecious genus of 96 taxa confined almost entirely to the Cape Floristic Region. To confirm whether these transitions took place, we carried out experimental tests for wind pollination and sampled insect flower visitors in 15 Leucadendron species, representing six clades in the genus. Methodology. In three clades in which an insect-wind shift has been inferred, we sampled species with traits suggestive of either wind or insect pollination. Plants were bagged with fine-mesh exclusion bags that excluded insects but allowed the passage of airborne pollen. Insects visiting female inflorescences were collected for identification and analysis of their pollen loads. Pivotal results. We found that insect exclusion had little effect on seed set of five species conforming to the wind pollination syndrome (L. rubrum, L. salicifolium, L. dubium, L. coniferum, and L. teretifolium), while seed set was strongly reduced by insect exclusion in the remaining 10 species conforming to an insect pollination syndrome. The most common pollinator of the insect-pollinated species was the nitidulid beetle Pria cinerascens. Conclusions. This study provides experimental verification of contrasting insect and wind pollination systems in Leucadendron and will thus enable formal phylogenetic tests of adaptive changes in floral traits, such as color and scent, that may be associated with pollination system transitions in this diverse lineage.