The Evolution of Dioecy and Sexual Dimorphism: An Integrative Approach Using a Gynodioecious Strawberry

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9707247 Ashman Separate male and female flowering plants (dioecy) have evolved from hermaphrodite ancestors independently in numerous lineages, leading evolutionary biologists to conclude that such a transition is a central problem in biology. However, we do not have a complete picture of how this transition occurs. An intensively modeled theory predicts that populations with females and hermaphrodites are an intermediate step to dioecy. The presence of females is expected to result in selection on hermaphrodites to become more male in gender, and if certain genetic conditions exist then dioecy can evolve. This research will address the potential for dioecy to evolve by characterizing the genetic architecture of a model system, the wild strawberry (Fragaria virginiana), that exhibits a transitional breeding system and among-population variation in a fundamental aspect of the selective environment (the frequency of females). By characterizing the genetic relationships among reproductive traits (pollen production, fruit set, and petals) in four populations of wild strawberry (two from each end of the female frequency continuum), this research will not only reveal the potential for response to selection, but it will also evaluate the assumptions and the robustness of theoretical models of reproductive evolution. Furthermore, among-population comparisons will yield information on the constancy of genetic parameters and the consequences of such constancy for evolutionary change. This research will provide information on the evolution of reproductive systems, information that is fundamentally relevant to evolutionary biology because all organisms face allocation decisions similar to the reproductive allocation decisions studied here. Plant reproductive systems are like many other systems where organs are functionally and structurally homologous, and thus necessarily have a shared developmental and genetic basis. Gaining an understanding of the constraints imposed by genetic architectur e on the evolution of individual phenotype and sexual dimorphism is an essential aspect of evolutionary biology. Furthermore, comparisons among populations will provide information on the lability of genetic architecture and will make a significant contribution to testing the assumptions of quantitative genetics as applied to evolutionary questions.