Hybridization and introgression in Hill's oak (Quercus ellipsoidalis)
Oaks (Quercus: Fagaceae) are renowned for their taxonomic difficulties, and in fact they have been referred to as a "worst case scenario for the biological species concept" (Coyne and Orr 2004). Work in my lab focuses on a morphologically variable Great Lakes endemic, Hill's oak (Quercus ellipsoidalis E. J. Hill), which ranges from sandy soils in the northern portions of its range to silty and even calcareous soils in the greater Chicago region. The species is arguably the Midwest's most problematic member of the black oak section and is distinguished by the sheer number of workers who have puzzled over its taxonomic status and proper identification. In our published work, we have demonstrated that the species is taxonomically distinct from both black oak (Q. velutina Lam.) and scarlet oak (Q. coccinea Münchh.) but that there appears to be introgression between black oak and Hill's oak. We are currently investigating patterns of gene flow among these species using AFLP, microsatellite, and micromorphological characters.
This project has several components:
- Identifying the limits of oak species, and identifying molecular and morphological markers useful for discriminating oak species. Our work demonstrates that even contentious oaks (e.g., Q. ellipsoidalis) are often distinguishable in spite of ongoing hybridization with other species. We are using a combination of light microscopy, scanning electron microscopy, and molecular data (both AFLP and microsatellites) to find characters that identify species and their hybrids. In the next phase of this work, we will be using ecological niche modelling to predict species distributions as a complement to observed patterns of morphological and genetic variance.
- Estimating the extent and pattern of introgression among oak species. We are using geographically widespread population samples to evaluate whether oak species are genetically coherent across their ranges and a combination of genetic and morphological data to evaluate what characters are good predictors of genetic admixture. This has practical ramifications for practicing ecologists and botanists, and it generates hypotheses regarding the correlation between morphological and molecular estimates of genetic admixture in forest trees.
- Identifying genomic patterns in genetic differentiation among oak species. In collaboration with Jeanne Romero-Severson, we are initiating a study of the genomic distribution of markers that show high differentiation among species. Our overarching questions are whether species-specific regions of the genome are clustered, with admixture evident across the remainder of the genome; and whether divergent regions are conserved across species.
- Phylogenetics and comparative analysis
- Plant taxonomy and floristics
- Molecular ecology
- Chromosome evolution
- Datasets and code
- Systematics and genome evolution in Carex subg. Vignea
- Interaction between gene flow and chromosome rearrangement in Carex scoparia
- Molecular genetic evidence of serpentine adaptation in Quercus ilex
- Patterns of hybridization in the Hill's oak group (Quercus ellipsoidalis and relatives)
- Systematics of elms (Ulmus)
- Reconstructing continuous character transitions on phylogenetic trees
Quercus ellipsoidalis SEM slideshow