DEVELOPMENTAL PLASTICITY, GENETIC-VARIATION, AND THE EVOLUTION OF ANDROMONOECY IN SOLANUM-HIRTUM (SOLANACEAE)

Studies of andromonoecious species have shown that sex expression (pro portions of hermaphrodite and staminate flowers) is quite variable. It is not known, however, whether this variation is due to variation amo ng individuals for genetically fixed patterns of allocation to stamina te and hermaphrodite flowers (population level variation) and/or to de velopmental plasticity of individuals in a heterogeneous environment ( organismal level variation). Distinguishing between these two levels o f variation is important for understanding the evolution of andromonoe cy. This study investigates levels of variation in sex expression in t he andromonoecious Solanum hirtum. Sex expression in this species is s hown to be plastic among individuals of the same genotype (organismal level variation) and determined, in part, by the resource status of th e individual. Among the genotypes examined there is also genetic varia tion for developmental plasticity. Thus, developmental plasticity can potentially respond to selection, and the evolution of this developmen tal system may have been instrumental in the establishment and mainten ance of andromonoecy in S. hirtum.