John H. Willis
Professor, Department of Biology, Duke University, Durham, NC 27708
What evolutionary processes influence genetic variation within species? What kind of molecular genetic changes underlie the evolution of adaptive traits and new species? How do ecological and genomic factors interact to cause the origin of new, reproductively isolated species? These are some of the most fundamental yet largely unanswered questions in biology. My lab’s research addresses basic evolutionary questions about the nature of adaptation and the origin of species. In particular, we are mainly interested in identifying the genomic basis of complex trait variation within and among populations and recently diverged species, in order to discover how populations are transformed into reproductively isolated species. We employ an integrated approach, combining the use of field studies, high throughput forward genetics, and comparative genomics in our experimental studies of wild plant species.
In our recent work, we have identified key genomic regions associated with ecologically important variation within and among closely related species of wildflowers in the genus Mimulus, an emerging model system for ecology and evolutionary studies. Our studies focus on the Mimulus guttatus species complex because it presents broad genetic diversity of floral morphologies and mating systems (large-flowered, bee-pollinated outcrossers to minute-flowered, self-fertilizing species), and specific physiological, morphological, and life history adaptations to local habitats that vary spectacularly in elevation (Pacific coast to above timber line), latitude (Aleutian Islands of Alaska to Mexico), seasonal soil moisture (edges of permanent streams and lakes, to meadows, rocky outcrops, and desert washes that dry completely in the summer), and unusual and often toxic soil conditions (including copper mine tailings, serpentine soils, saline soils, rocky cliffs, thermal soils of hot springs).
The plants in the Mimulus guttatus species complex have numerous qualities that allow investigators to readily dissect this profound ecological and evolutionary diversity using powerful forward genetic approaches. The phenotypically diverse populations, ecological races, and biological species often are fully interfertile or display only incomplete post-pollination crossing barriers. Mimulus guttatus and relatives are easy to cultivate by the thousands in the greenhouse, and their high fecundity (>1,000 seeds per plant), and rapid generation time (~2 months from seed to seed) make large-scale genetic mapping studies possible. Until recently, however, such approaches were not feasible because of a lack of molecular genetic tools for these plants. To facilitate these studies, we are leading collaborative efforts to develop genomic resources for Mimulus. We now have developed extensive EST databases, thousands of highly variable genetic markers, integrated BAC physical and genetic maps, stable transformation methods, and methods for quantifying genome-wide patterns of tissue and environmental specific gene expression. In collaboration with DOE’s JGI, we have just completed an annotated draft whole genome sequence for M. guttatus that is to be publicly released in late 2009, and we have initiated resequencing studies of other members of the species complex.
Already these genomic tools are allowing us to dissect key genomic regions that affect ecologically important traits down to the individual genes, and to investigate the molecular and ecological mechanisms underlying adaptive variation and speciation.