Genetic variation in wild populations of rain-forest trees

Abstract

IN the tropical rain forest, many tree species grow close together, and they are apparently equivalent in their edaphic requirements and spatially interchangeable. Most species occur at low density although they may be geographically widespread. No other plant community contains as many species of a single life form as do certain mixed dipterocarp forests of the aseasonal wet lowlands of Malesia^1–3. Such a population structure and level of diversity makes it hard to see how speciation has occurred. Spatial isolation of individuals and the abundant, normally hermaphrodite flowers simultaneously available for fertilisation in the canopy of the dipterocarp emergents suggest the possibility of self-fertilisation, but many of the understorey species are dioecious. As part of a comparative study of the reproductive biology of rain forest tree species, intra-specific genetic variation of isozymes has been demonstrated for the first time in an emergent and an understorey species of rain forest trees. Polymorphism is common in both species and there is evidence for short-range spatial heterogeneity in gene frequency and also in leaf morphology.