Isozyme Variation in Some Rain Forest Trees

Abstract

Starch gel electrophoresis has been carried out on leaf extracts of Shorea leprosula, S. ovalis, and Xerospermnum intermedium, rain forest trees growing in South-west Malaysia. A high level of intra-population genetic variation is indicated by electromorphic frequencies obtained from S. leprosula and X. intermedium extracts, but not so for S. ova/is extracts which yielded remarkably uniform electromorph patterns. Evidence is presented for genetic differences between age classes. IN THE TROPICAL RAIN FOREST there is a great abundance of tree species which grow close together, appear to be equivalent in their edaphic requirements, and are apparently spatially interchangeable. These features are most dramatically displayed in certain mixed dipterocarp forests of the aseasonal, wet lowlands of Malesia and thereby pose problems as to the origin of such an immense species diversity. Although spatial isolation and the abundance of normally hermaphrodite flowers in the canopy of the very tall, emergent species suggest that self-fertilization may occur, many understory species are dioecious.