OPUS: MCS: Evolutionary processes underlying transitions in sexual systems, pollination mode and ploidy

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Many crops responsible for the bulk of human nutrition are pollinated by wind. Wind pollination has evolved repeatedly from insect pollination in flowering plants, yet the underlying mechanisms are poorly understood. Shifts to wind pollination from animal pollination and to separate sexes (dioecy) from hermaphroditism represent major evolutionary transitions in flowering plants. Early progress in understanding the evolution of wind pollination was made in a plant genus where multiple origins of wind pollination from insect-pollinated ancestors is accompanied by the separation of sexes and the duplication of genomes, also known as polyploidy. Thalictrum are herbaceous perennials with great diversity of flower morphology, sexual system, and pollination mode amongst its circa 200 temperate species growing worldwide. Although polyploidy has a long history of recognized relevance to the evolution of plants, and a demonstrated contribution to increased species diversity, few studies have examined whether polyploidy is associated with shifts in pollinators or sexual system. This study will contribute to a better understanding of the processes contributing to changes in plant reproduction, with potential applications to agriculture, where alternative pollination vectors may be needed due to shortage of insect pollinators, and separate sexes are useful in the production of hybrid seed.This study seeks to investigate the order of trait evolution and the phylogenetic patterns of trait-dependent species diversification in a diverse angiosperm lineage where evolutionary transitions in ploidy level, sexual system and pollination mode have occurred repeatedly. Thalictrum (Ranunculaceae) is an ideal system in which to study the tempo and mode of evolution of these ecological shifts, as they have occurred repeatedly, allowing for multiple comparisons. The broader questions addressed by this study are: 1) What is the effect of polyploidy, sexual system and pollination mode on net diversification rates? Do polyploidy and animal pollination promote speciation? Is dioecy an evolutionary "dead end"?; and 2) What is the order of character evolution? Is transition to unisexual flowers more likely in a wind pollinated background or did unisexual flowers evolve first? Are either of these more likely in a polyploid background? This interdisciplinary research will make use of phylogenetic comparative analyses to uncover trait-dependent species diversification that will inform future evolutionary development experiments aimed at uncovering the genetic basis underlying independent shifts to wind pollination, dioecy and polyploidy and at determining whether these evolved through same or different genetic mechanisms each time, i.e., is it a case of parallel or convergent evolution?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.