EVOLUTIONARY SIGNIFICANCE OF LOCAL GENETIC DIFFERENTIATION IN PLANTS

The study of natural plant populations has provided some of the strong est and most convincing cases of the operation of natural selection cu rrently known, partly because of amenability to reciprocal transplant experiments, common garden work, and long-term in situ manipulation. G enetic differentiation among plant populations over small scales (a fe w cm to a few hundred cm) has been documented and is reviewed here, in herbaceous annuals and perennials, woody perennials, aquatics, terres trials, narrow endemics, and widely distributed species. Character dif ferentiation has been documented for most important features of plant structure and function. Examples are known for seed characters, leaf t raits, phenology, physiological and biochemical activities, heavy meta l tolerance, herbicide resistance, parasite resistance, competitive ab ility, organellar characters, breeding systems, and life history. Amon g the forces that have shaped these patterns of differentiation are to xic soils, fertilizers, mowing and grazing, soil moisture, temperature , light intensity, pollinating vectors, parasitism, gene flow, and nat ural dynamics. The breadth and depth of the evidence reviewed here str ongly support the idea that natural selection is the principal force s haping genetic architecture in natural plant populations; that view ne eds to be more widely appreciated than it is at present.