REPRODUCTIVE BIOLOGY OF TROPICAL LOWLAND RAIN FOREST TREES. I. SEXUAL SYSTEMS AND INCOMPATIBILITY MECHANISMS

Sexual systems of tropical lowland rain forest trees were investigated to estimate the relative proportions of hermaphroditic, monoecious, and dioecious species. Controlled hand pollinations were performed on hermaphroditic species to determine the proportions of self-compatible and self-incompatible species. A total of 333 species was examined; 65.5% species were found to be hermaphroditic, 11.4% monoecious, and 23.1% dioecious. There were no differences between canopy and subcanopy habitats in the distribution of various sexual systems. Out of the 28 species subjected to controlled pollinations, 24 showed the presence of self-incompatibility. The site of the incompatibility barrier in distylous species was either in the stigma or in the style. In most of the monomorphic species, the incompatibility barrier was in the ovary. Although a majority of tree species in the rain forest appear to be obligate outcrossers (xenogamons), the potential for inbreeding due to small effective population size still remains to be explored.