This research will test three specific hypotheses that may account for the maintenance of non-functional anther and pollen production in functionally female plants of Thalictrum polygamum, a native perennial plant with a cryptically dioecious breeding system. Anther and pollen production may remain in females as a reward for insect pollinators because of selection pressure for increased insect visitation (Adaptation Hypothesis); as a correlated response because of selection maintaining anther and pollen production in males (i.e. a strong, positive genetic correlation exists between anther and pollen production in males and females, Genetic Constraint Hypothesis); or as vestiges of the ancestral cosexual state because there is little or no selective benefit to their removal (i.e. no "cost" to females for production of anthers and pollen, Ancestry Hypothesis). The second portion of this project will evaluate the evolutionary pathway by which dioecy has evolved in the T. polygamun, the possible role of resource reallocation as a selective force important to this transition, and the relevance of wind pollination to the change.
