Collaborative Research: Does genetic load drive mating system evolution? Tests in an explicit historical context

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This research will quantify the interplay between historical events and current natural selection in shaping plant mating system. Evolution is an ongoing process but depends strongly on the past. While nearly everyone acknowledges this fact, it has been difficult to quantify the relative importance of historical and current selection pressures as explanations of patterns in nature. This research will look at the factors that have determined the amount of self-pollination versus outcrossing in the American bellflower (Campanulastrum americanum). The project will immerse undergraduate and graduate students in the collection of next-generation DNA sequence data to reconstruct historical events and studies of current selective environment in the study species. Analyses of data from these disparate sources into a single, unified framework will provide a clearer understanding of the processes shaping complex patterns in nature, and yields a predictive framework that can be applied in any biological system. Broad dissemination of this predictive approach is valuable because it will help predict the response of species to increasingly altered environments in the modern age.Plant mating systems are evolutionarily labile, ranging from highly outcrossing to highly inbreeding. This wide variation provides an excellent system for understanding the ultimate drivers of evolutionary change. Variable mating system strategies across levels of the biological hierarchy are commonly explained as adaptations to the current selective environment. A significant fraction of this variation, however, may reflect historical evolution in response to colonization during range expansion. This idea will be tested using Campanulastrum americanum, a North American herb in which preliminary data indicate reduced inbreeding depression and greater autogamy in sites where phylogeographic data suggest recent colonization. Using populations a range of distances from glacial refugia, the researchers will gather data with coalescent analysis of RAD-seq polymorphism, greenhouse studies of fixed and segregating genetic load, field studies of pollen limitation and reproductive assurance, and population-genetic inferences of selfing rates. Analyses of these data will determine whether initially non-adaptive processes associated with range expansion provided a permissive environment for later evolution of the mating system. The research framework therefore provides a mechanism for discerning the ultimate drivers of organismal change across past and present time scales.