A Genetic and Genomic Perspective on the Role of Polyploidization in Phenotypic Evolution in Mimulus sookensis

Polyploidy is ubiquitous among angiosperms, yet the contribution of whole genome duplications to long-term diversification patterns is unclear. Recent experimental work in several polyploid species has revealed that meiotic pairing and recombination between homeologs may cause loss of one parental copy while the other copy is duplicated. Mimulus sookensis is a hybrid tetraploid that has formed repeatedly throughout its range.  Like one of its diploid progenitors, M. nasutus, M. sookensis has tiny, self-fertilizing flowers that are much smaller than the showy, predominately outcrossing flowers of its other diploid progenitor, M. guttatus. Importantly, both diploid and synthetic allotetraploid F₁ hybrids of M. guttatus and M. nasutus have flowers that are almost as large as those of M. guttatus. This raises the question as to how M. sookensis have evolved M. nasutus-like small, selfing flowers. To address the evolution of flower size in M. sookensis, I employed two approaches.  First, I compared whole-genome sequences of two M. sookensis lineages with the genomes of their progenitor species to investigate the possibility that homeologous recombination caused a loss of M. guttatus floral alleles, leading to the M. nasutus-like phenotype of M. sookensis. Second, in order to identify genomic regions responsible for small flower size in M. sookensis, I crossed M. sookensis with a large-flowered, synthetic allotetraploid to generate an F₂ mapping population. I then used a genotyping-by-sequencing approach to map floral QTLs. These two approaches provide unprecedented insight into genome evolution and its phenotypic consequences in a naturally-occurring allotetraploid plant species.