Sheri A. Church Assistant Professor of Biology Molecular Evolution and Bioinformatics Department of Biological Sciences George Washington University 2023 G Street. NW Washington, D.C. 20052 333 Lisner Hall (office); 408 Bell Hall (lab) Tel. Office: (202) 994-0274 Tel. Lab: (202) 994-4412 Fax: (202) 994-6100 E-Mail: schurch (at) gwu.edu

   My research focuses on speciation and understanding the genetic changes associated with species diversification and radiation.  Speciation is the foundation of biological diversity and, therefore, one of the most important processes in evolution.  My research blends molecular and bioinformatics approaches to understand the history of species diversification in various lineages.  Ultimately, the goal is to understand the genetic basis of speciation.

   Speciation and Molecular Evolution in Houstonia.
My dissertation work  focused on the North American Houstonia , a group of herbs belonging to the madder family (Rubiaceae).  The genus is composed of 20 species that are distributed throughout the United States (except the far west) and Mexico.  Speciation in this lineage has been accompanied by changes in the basic chromosome number of the major clades.  The loss of chromosomes was also associated with changes in distribution.  The resulting pattern shows that this lineage originated in sub-tropical Mexico, proceeded north into the southwestern U.S., and then spread to the central and finally eastern U.S., with each change in distribution being accompanied by the loss of a chromosome.

Evolution of Polyploidy and Speciation. Within the Houstonia lineage, there are both hybridizing and non-hybridizing species.  The non-hybridizing species are either diploid or else do not have similar polyploid chromosome numbers.  However, the hybridizing lineages are generally polyploid.  Furthermore, the only species that are currently polyploid are those with the most reduced chromosome numbers in the lineage.  The oldest species in the lineage have chromosome numbers that indicate ancient polyploidization, although none of these species are currently considered polyploid.  As the number of chromosomes was reduced, a second round of polyploidization appears to be occurring in the most reduced genomes, suggesting a cycle of polyploidy and chromosome loss in this lineage.  This cycling of polyploidy, chromosome loss, and subsequent re-polyploidization is the same process that is thought to be fundamental to the evolution of eukaryotic genomes.  Currently, I am investigating moecular approaches to unravel the history of chromosome loss and polyploidization in these species.

Speciation Genetics in Sunflower. With the recent growth in the number of sequencing projects, portions and complete genomes of many organisms are being sequenced.  With this wealth of sequence data, a genome level approach for identifying speciation genes is quickly becoming feasible.  With my post-doctoral advisor and several other collaborators, I am using a large-scale genome-level approach to identify candidate speciation genes in several closely related sunflower (Helianthus) species.  Specifically, I am performing a comparative analysis of EST (expressed sequence tag) sequences to identify genes with high rates of evolution that may be involved in speciation or adaptation.  These genes, now identified, are the focus of follow up studies to determine their patterns of evolution and expression across various sunflower species. (Collaborators: L. H. Rieseberg, Indiana Univ.; K. Livingstone, Trinity Univ.)

Appalachian Phylogeography. Very little is known about the flora and fauna of the Southern Appalachians between the late Tertiary and the most recent Wisconsin glaciation.  The occurrence of disjunct populations of Coastal Plain and or Midwestern and Northern species in the Southern Appalachians can be attributed either to recent migration, or, alternatively, that these populations are remnants of a more widespread floral and fauna of the late Tertiary, during which warmer conditions prevailed.           Initially, we investigated these alternative hypotheses looking at the phylogeographic history of one such disjunct species, Ambystoma tigrinum tigrinum . The results of this study show that the mountain population is unique from all other populations and probably became isolated from more southern populations ~150-250 kya. These results suggest that this population may have been part of a Pleistocene refugium, possibly harboring many other disjunct species throughout the Pleistocene.  Preliminary surveys (in collaboration with Henry Wilbur at the University of Virginia) of several of these disjunct plant species show phylogeographic patterns similar to those of the tiger salamander, supporting the hypothesis that this region may have been a Pleistocene refugium.  This research is ongoing in the lab.

Speciation Theory. There are many aspects of speciation that are more tractable through mathematical modeling than through experimental analysis.  One such aspect is the effect of migration on the probability of speciation.  I have constructed a mathematical model to look at the effects of low levels of migration between divergent populations on the time to speciation under the Dobzhansky – Muller model of speciation.

For reprint requests, please send an email to schurch (at) gwu.edu .

Church, S. A., K. Livingstone, Z. Lai, A. Kozik, R. Michelmore, S. Knapp, and L.  H. Rieseberg. (2006). Using variable rate models to identify genes under selection in sequence pairs: their validity and limitations for EST sequences.  Journal of Molecular Evolution In Press.

Lai, Z., K. Livingstone, Y. Zou, S. A. Church, S. Knapp, J. Andrews, and L.H. Rieseberg. (2005) Identification and mapping of SNPs from ESTs in sunflower.   Theoretical and Applied Genetics 111(8): 1532-1544. 

Church, S. A., and D. R. Taylor. (2005) Speciation and hybridization among Houstonia (Rubiaceae) species: The influence of polyploidy on reticulate evolution.  American Journal of Botany 92: 1372-1380.

Rieseberg, L. H., S. A. Church, and C. L. Morjan. (2003) Integration of populations and differentiation of species.  New Phytologist 161: 59-69.  
 
Church, S. A.  (2003) Molecular phylogenetics of Houstonia (Rubiaceae): descending aneuploidy and breeding system evolution in the radiation of the lineage across North America.  Molecular Phylogenetics and Evolution 27: 223-238.

Church, S. A., J. Kraus, J. C. Mitchell, D. R. Church, and D. R. Taylor. (2003)  Evidence for multiple Pleistocene refugia in the postglacial expansion of the eastern tiger salamander, Ambystoma tigrinum tigrinum.  Evolution 57(2): 372-383.

Church, S. A., and D. R. Taylor.  (2002)  The evolution of reproductive isolation in spatially structured populations.  Evolution 56(9): 1859-1862.

Richards, C., S. Church, and D. McCauley. (1999) The influence of population size and isolation on gene flow by pollen in Silene alba.  Evolution 53(1): 63-73.

Bioinformatics. BISC 184 / CS 177.  A lecture and lab course designed to bridge computer science and biology.  The course introduces techniques in bioinformatics such as database searching, sequence alignment, protein 
translation and protein folding.  Offered spring semesters.

Ecological and Evolutionary Genetics.  Bisc 163.  This course will be offered in alternating fall semesters.  Topics to be covered include advanced population genetics and ecological genetics such as measures of selection, drift, phenotypic plasticity, etc.

Molecular Evolution. BISC 224. This course will be offered in alternate fall semesters to gradauate students and advanced undergraduates. Topics to be covered include Measuring selection via substitution rate analyses, molecular clocks, genome evolution and polyploidy, evolution of gene families, and population level processes. 

Current Topics in Evolutionary Ecology. BISC 206.  A graduate seminar discussion group integrating ecology and evolution.  The course will include discussion of relevant new literature in the field.  Offered each semester.

Students who are interested in joining the lab should contact me directly.  Anyone interested in using molecular or bioinformatics approaches to answer evolutionary questions is encouraged to apply.  My interests are quite broad, and so I encourage students to explore their interests as well.  Funding is available for Ph.D. students through departmental fellowships and TA positions; however, I encourage students to apply for outside funding as well.

Department of Biological Sciences
Bioinformatics at GWU
George Washington University
National Museum of Natural History  
Compositae Genome Project Database
NCBI