Evolution of Dioecy from Distyly and the Impact of Recent Landscape Changes on the Reproductive Systems of Cordia spp in the Guanacaste Region of Costa Rica

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0212742BawaBreeding systems, a keystone feature of the life history of plants, are known to be diverse and mutable. Two breeding systems of particular note are distyly and dioecy. Distyly, with self-incompatible hermaphroditic individuals of two types, has evolved multiple times in flowering plants. Mating of the two types of individuals, (those with long styles and short stamens (pin) and those with short styles and long stamens (thrum)), is generally restricted to crosses between types. Dioecious species, on the other hand, have separate male and female (unisexual) individuals. There are many examples of closely related species (Cordia spp. is one) that possess these alternative breeding strategies and it has been repeatedly suggested that dioecy has evolved from distyly. Yet no genetic tests nor ecological studies have been made to confirm or refute the likelihood of this evolutionary pathway. The first objective of this research is to use molecular phylogenetic techniques to reconstruct the phylogeny of Cordia spp. and to map changes in breeding system onto it. The second objective is to use DNA markers to identify regions linked to sex-determining genes in dioecious species and to flower morphology (pin and thrum) in distylous species. These markers will be utilized to characterize the genetic basis of each breeding system, the likelihood of a common origin, and the specific steps that lead to changes. These studies will provide information about the direction of evolutionary change in breeding systems in a tropical tree. This work will lay the foundation for future studies on how breeding system evolution occurs within the context of rapidly changing environments (e.g., changes in the pollinator community brought on by landscape-level disturbance), a topic of considerable importance for conservation biology. The research will also impact human resource development because of PIs' strong commitment to provide research opportunities for female students and for students from groups under-represented in science (e.g., through our summer Research Experience for Undergraduates (REU) programs, McNair fellowships and Undergraduate Mentoring in Environmental Biology (UMEB)). In addition the project will train graduate students and post doctoral associates.