A CONCEPTUAL-FRAMEWORK FOR THE ANALYSIS OF PHENOTYPIC PLASTICITY AND GENETIC CONSTRAINTS IN PLANTS

A plant genotype can potentially exhibit a variety of phenotypes, depending on environmental conditions. If the quantitative measure of a life history trait is defined as the phenotypic value, one can then define an optimum phenotypic value obtainable by a genotype in an ideal, nonlimiting environment. Analogous to niche theory, the fundamental phenotype (F) describes an individual at its optimum phenotypic value, while the realized phenotype (R) describes an individual at some fraction of its fundamental phenotype. given the presence of limiting factors. I hypothesize that the range of fundamental phenotypes found in a population affects future evolutionary potential because genetically based differences between realized phenotypes translate into fitness differences between genotypes. The range should be greatest where environmental conditions are most spatially and temporally variable. I also predict that the disparity between F and R will increase as environments become increasingly variable and/or selection pressures become more severe. One application of the R/F concept should be for studies that attempt to measure fitness and natural selection in wild populations. By defining F for a genotype and then planting clones of that genotype into different habitats, one can calculate R for specific traits of interest and obtain an idea of the strength of selection in the habitats. Fundamental phenotypes can also be used to identify factors that limit plant growth and reproduction in nature. Reciprocal transplant techniques using easily cloned plant species should be very useful in determining R/F ratios.