Doctor of Philosophy / Department of Biology / Carolyn J. Ferguson / Morus L. (Moraceae) is a temperate and subtropical genus of ten to 15 species distributed in Asia, Africa, Europe, North, Central and South America. Despite its broad distribution and economic importance, it has received little attention from systematic botanists. Two species of this genus, the native M. rubra and the exotic M. alba, co-occur in eastern North America including the Flint Hills region of the Central Plains. In my dissertation research, I have conducted both species level and population level studies to obtain insights into the diversification of Morus. At the species level, my objectives were to re-evaluate the taxonomy and reconstruct the phylogeny of Morus. Based on herbarium and literature study as well as some field study, I recognize 13 species: eight species occurring in Asia, one in Africa and four in the New World. I used sequence data from the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA and the trnL-trnF region of the chloroplast DNA to reconstruct the evolutionary history of Morus. The phylogenies were congruent and indicate a) a monophyletic core group of Morus with two well-supported geographical clades (one containing Asian taxa and one of New World taxa); and b) that Morus, as currently circumscribed, is non-monophyletic. At the population level, I studied sex expression pattern variation between the Morus native-exotic pair in the Flint Hills region, and assessed hybridization between these species at Konza Prairie Biological Station (KPBS). Both species are subdioecious, and Flint Hills populations exhibit significantly male-biased sex ratios, with sex expression being size independent. Approximately 10% of individuals of each species changed sex annually. In the population study at KPBS, I applied randomly amplified polymorphic DNA (RAPD) markers and microsatellites. The Morus species were moderately ([Theta]II = 0.079; RAPD data) to highly differentiated genetically (F[subscript]ST = 0.233; microsatellite data). Analysis of genetic structure suggested interspecific gene flow and indicated the presence of later generation hybrids. The presence of the exotic congener may affect the existence and genetic integrity of the native species. Overall, these studies contribute to our understanding of diversity in this interesting plant study system.

Flowering plants display diverse reproductive systems, including a variety of gender strategies and mechanisms of clonal propagation. Here, I investigate gender strategies, sex-ratio evolution, and sexual dimorphism in the North American clonal aquatic, Sagittaria latifolia (Alismataceae), which exhibits three sex phenotypes (hermaphrodites, females, males) and two modal sexual systems (monoecy, dioecy). This provides an outstanding opportunity to examine the costs and benefits of combined versus separate sexes. My research focused on the northern range limit in eastern N. America, and on disjunct populations in western N. America. I developed microsatellite (SSR) markers to investigate population genetic structure at several spatial scales, including the clonal structure of local populations to continental patterns. These analyses provided insights on the roles of historical, ecological and reproductive factors in the evolution and maintenance of sexual system diversity. Phenotypic sex ratios varied near continuously from monoecy through subdioecy (three sex phenotypes) to dioecy. A comparison of phenotypic and genotypic sex ratios in dioecious populations demonstrated close correspondence. The northern range limit was characterized by a decline in female frequency and an increased incidence of subdioecy. I evaluated two hypotheses to explain this pattern: (1) increased sex inconstancy in dioecious populations; (2) hybridization between monoecious and dioecious populations. I found support for both hypotheses, although hybridization appears to be the more common pathway to subdioecy. I parameterized a model predicting female frequency and hermaphrodite sex allocation; observed and predicted values were correlated suggesting that subdioecious populations are closer to equilibrium than expected for a clonal perennial. A comparison of eastern and western populations indicated genetic differentiation between monoecy and dioecy in the east, but in the west, due to habitat isolation, geography plays a more important role in genetic differentiation. Evidence from cpDNA haplotype variation indicated that the western range was established following long-distance colonization from the east involving a genetic bottleneck. The discovery of gynodioecious populations of S. latifolia in the west, and the absence of ecological and genetic differentiation between monoecious and dioecious populations, raise the possibility that dioecy may have evolved autochthonously in the west, and more recently than in the eastern range.

Flowering plants display diverse reproductive systems, including a variety of gender strategies and mechanisms of clonal propagation. Here, I investigate gender strategies, sex-ratio evolution, and sexual dimorphism in the North American clonal aquatic, Sagittaria latifolia (Alismataceae), which exhibits three sex phenotypes (hermaphrodites, females, males) and two modal sexual systems (monoecy, dioecy). This provides an outstanding opportunity to examine the costs and benefits of combined versus separate sexes. My research focused on the northern range limit in eastern N. America, and on disjunct populations in western N. America. I developed microsatellite (SSR) markers to investigate population genetic structure at several spatial scales, including the clonal structure of local populations to continental patterns. These analyses provided insights on the roles of historical, ecological and reproductive factors in the evolution and maintenance of sexual system diversity. Phenotypic sex ratios varied near continuously from monoecy through subdioecy (three sex phenotypes) to dioecy. A comparison of phenotypic and genotypic sex ratios in dioecious populations demonstrated close correspondence. The northern range limit was characterized by a decline in female frequency and an increased incidence of subdioecy. I evaluated two hypotheses to explain this pattern: (1) increased sex inconstancy in dioecious populations; (2) hybridization between monoecious and dioecious populations. I found support for both hypotheses, although hybridization appears to be the more common pathway to subdioecy. I parameterized a model predicting female frequency and hermaphrodite sex allocation; observed and predicted values were correlated suggesting that subdioecious populations are closer to equilibrium than expected for a clonal perennial. A comparison of eastern and western populations indicated genetic differentiation between monoecy and dioecy in the east, but in the west, due to habitat isolation, geography plays a more important role in genetic differentiation. Evidence from cpDNA haplotype variation indicated that the western range was established following long-distance colonization from the east involving a genetic bottleneck. The discovery of gynodioecious populations of S. latifolia in the west, and the absence of ecological and genetic differentiation between monoecious and dioecious populations, raise the possibility that dioecy may have evolved autochthonously in the west, and more recently than in the eastern range.