The Genetics of Dimorphism and Reproduction in Plant Populations

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The evolution of populations is characterized by a balance between factors acting to promote change and genetic constraints imposed on such change. In the present study, the evolution of morphological differences between the sexes (sexually dimorphic traits) within dioecious populations is being used as a model system to investigate this balance. The evolution of sexually dimorphic traits involves genetic tradeoffs between male and female reproductive performance. Such tradeoffs are the result of genetic correlations between the sexes, which in turn reflect the extent to which corresponding traits in the two sexes, such as flower size, are controlled by similar genetic influences. In the previous funding period, males and females of the dioecious plant Silene alba were subjected to sex-specific selection for calyx diameter and flower number to evaluate both the genetic basis for these traits in the sex under selection and to assess correlated response in the other sex. This work has generated populations in which males have become either more extremely male-like or more female-like, and a similar series of populations for female traits. The primary objective of the proposed study is to take males (or females) from these different lines, place them in a semi-natural environment, and evaluate their comparative reproductive performance. Thus it will be possible to evaluate the consequences of modifying such traits in either male or female plants, and by evaluating performance of their female or male relatives, respectively, to determine the genetic consequences of correlated response to selection in the sex not under direct selection. This work will contribute to our overall understanding of the evolutionary dynamics of sexually dimorphic traits as well as the affects of genetic correlations between the sexes.