Venable 9801391 The selective forces responsible for the evolution of gender specialization are being investigated in Lycium (Solanaceae), a genus of desert shrubs, using a phylogenetic framework. Lycium is unusual in possessing both hermaphroditic and separate-sexed species and in having multiple evolutionary origins of separate sexes. Specifically, the importance of selection for outcrossing will be estimated through investigation of self-compatibility, inbreeding depression, and natural selfing rates. Also, whether females compensate for loss of male function by reallocating resources and the importance of this compensation effect will be determined using data collected for several reproductive components. A model is developed that enables us to evaluate the significance of these components to the evolution of gender specialization. These two hypotheses will be explicitly tested by first inferring phylogenetic relationships (the evolutionary tree) in the genus, using both morphological and molecular data, and then making comparisons between dimorphic and monomorphic sister taxa. The evolution of gender systems is an important general issue in biology that has intrigued evolutionary biologists for decades. This research project will elucidate the selective forces operating on the evolution of gender specialization. Plants make excellent systems in which to study the evolution of gender, both because of their tremendous variation in gender systems and their ease of study in the field. Although gender specialization is a relatively rare condition (occurring in <10% of angiosperm species), its repeated evolution among many unrelated taxa makes it an important evolutionary issue. Comparative data have frequently been used to study the evolution of gender in plants, but the analyses have usually been flawed. There have been repeated calls for a more careful analysis of comparative data. The approach taken here, of combining field studies of function with sound phylogenetic comparisons, is one answer to this call, and will provide an important contribution to the evolutionary interpretation of gender specialization in plants.
