Evolution of Dioecy
Most flowers are hermaphroditic, with both male and female organs contained within a single flower. Unisexual flowers, with functionally male or female organs only, have evolved repeatedly in angiosperms. New Zealand has one of the highest proportions of unisexual flowers on separate plants (dioecy), with ~15% of the native flora demonstrating some form of sexual differentiation. We are examining the developmental and genetic basis of sex expression in ribbonwood (Plagianthus, Malvaceae), which has two endemic dioecious species.
Using ribbonwood as a model system for the recent evolution of dioecy, we hope to address two fundamental questions: 1) At what point in floral development does the alternate male/female whorl abort? and 2) What genes are responsible for determining gender? For this project, we are combining detailed microscopic analyses of the male and female flowers with genomic characterization of floral cDNA libraries using next-generation sequencing to gain insight into the earliest stages of gender evolution. This project is in collaboration with Dr. Barbara Ambrose at the New York Botanical Garden and Dr. Cynthia Skema of the Morris Arboretum.
Consequences of Whole Genome Duplication
Polyploidy, or whole genome doubling, has been a significant evolutionary force in flowering plant history. We are examining the genomic consequences of polyploidy using Tragopogon (Asteraceae) as a model system for natural and recurrent polyploid formation, in collaboration with Vaughan Symonds (Massey University) and the Soltis lab (University of Florida and Florida Museum of Natural History). We are particularly interested in understanding the repeatability of evolution as it pertains to 1) the formation of polyploids and 2) the fate of genes duplicated by polyploidy. To address these issues we are utilizing synthetic polyploid lines of T. miscellus and T. mirus and comparing their genotypes and genomic content to naturally occurring polyploids. Current projects are aimed at understanding cyto-nuclear interactions in the polyploids, methylation changes in polyploid genomes relative to their progenitors, and the genetic basis for morphological differences in reciprocally formed polyploids.
Phylogenetic Systematics of Malveae (Malvaceae)
Tribe Malveae is the largest in subfamily Malvoideae with approximately 75 genera and over 1000 species. Various collaborations are ongoing to reconstruct phylogenetic relationships of genera in the tribe and for the tribe itself. Some of our ongoing projects include: Origins and evolution of dioecy in Lawrencia, in collaboration with Bill and Robyn Barker at the State Herbarium of South Australia; reconstructing a chloroplast DNA phylogeny for the tribe Malveae, in collaboration with Randy Small at the University of Tennessee; speciation and diversification of the high Andean genus Nototriche, in collaboration with Mary Arroyo and Paola Jaraarancio(Chile).
