Evolutionary Genomics of Plant Adaptation and Speciation

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How new species arise has been a central focus of biology since the publication of Darwin's famous book, “On the Origin of Species.” However, the importance of the evolutionary processes that drive speciation remain controversial. In this project, I will conduct a series of experiments to test several unorthodox hypotheses about the formation of species in the plant kingdom, using wild sunflowers of the genus Helianthus as a model system. First, I will test whether sexual selection, which refers to competition for reproduction, is an important contributor to plant speciation. While sexual selection is known to be important in animals, its role in plant speciation is unknown. Second, I will determine whether natural selection against hybrids drives the evolution of barriers to cross-species mating. This hypothesis, known as speciation by reinforcement, was first put forward by the 19th century British naturalist Alfred Russel Wallace. However, empirical support for reinforcement is limited, perhaps because of a focus on costly visible traits such as flower color or flowering time. I will examine the possibility that reinforcement commonly involves cryptic mate choice mechanisms involving pollen-stylar interactions. Lastly, I will attempt to solve one of the oldest mysteries in speciation studies, which is how large-scale chromosomal rearrangements are established. Large rearrangements greatly reduce the fertility of the individual in which they first arise. Thus, according to evolutionary theory, the rearrangements should be eliminated from populations. Instead, they frequently become established. A possible explanation for this puzzle is a phenomenon called female meiotic drive, in which the rearrangement biases the outcome of meiosis (a key step in sexual reproduction) to make it more likely that the chromosome with the rearrangement ends up in the next generation. I will test whether rearrangements in Helianthus sunflowers exhibit meiotic drive. These projects will provide a first estimate of the importance of sexual selection and reinforcement in driving plant speciation, and may potentially solve an outstanding mystery about chromosomal evolution. Benefits to Canada include the training of highly qualified personnel in genomics and bioinformatics, the potential discovery of agriculturally valuable genes, and the development of genetic maps that will facilitate the introgression of such genes into cultivated sunflower germplasm. **