Journal of Heredity 2003:94(3)
© 2003 The American Genetic Association 94:197-204
The Wilhelmine E. Key 2002 Invitational Lecture. Phylogeography, Haplotype Trees, and Invasive Plant Species
From the Department of Biology, Washington University, St. Louis, MO 63130 (Schaal and Caicedo) and USDA Agricultural Research Service, Northern Plains Agricultural Research Laboratory, 1500 N. Central Avenue, Sidney, MT 59270 (Gaskin).
Barbara A. Schaal is Spencer T. Olin Professor of Biology at Washington University in St. Louis. She received her Ph.D. in population biology from Yale University and did postdoctoral work at the University of Georgia, and she was on the faculty at the University of Houston and Ohio State University before moving to Washington University in 1980. Dr. Schaal was president of the Botanical Society of America and has served as executive vice president of the Society for the Study of Evolution, for which she is currently president-elect. Additionally, she has served on editorial boards of numerous journals and was chair of the Department of Biology, Washington University. Dr Schaal currently serves as chair of the Scientific Advisory Council of the Center for Plant Conservation, chair of the NRC Committee on Agriculture, Biotechnology, Health and the Environment, and as a member of the board of trustees, Missouri chapter of The Nature Conservancy. She is a fellow of the American Association for the Advancement of Science, a John Simon Guggenheim Fellow, and a member of the U.S. National Academy of Sciences.
Address correspondence to Barbara A. Schaal at the address above.
The distribution of genetic variants in plant populations is strongly affected both by current patterns of microevolutionary forces, such as gene flow and selection, and by the phylogenetic history of populations and species. Understanding the interplay of shared history and current evolutionary events is particularly confounding in plants due to the reticulating nature of gene exchange between diverging lineages. Certain gene sequences provide historically ordered neutral molecular variation that can be converted to gene genealogies which trace the evolutionary relationships among haplotypes (alleles). Gene genealogies can be used to understand the evolution of specific DNA sequences and relate sequence variation to plant phenotype. For example, in a study of the RPS2 gene in Arabidopsis thaliana, resistant phenotypes clustered in one portion of the gene tree. The field of phylogeography examines the distribution of allele genealogies in an explicit geographical context and, when coupled with a nested clade analysis, can provide insight into historical processes such as range expansion, gene flow, and genetic drift. A phylogeographical approach offers insight into practical issues as well. Here we show how haplotype trees can address the origins of invasive plants, one of the greatest global threats to biodiversity. A study of the geographical diversity of haplotypes in invasive Phragmites populations in the United States indicates that invasiveness is due to the colonization and spread of distinct genotypes from Europe ( Saltonstall 2002). Likewise, a phylogeographical analysis of Tamarix populations indicates that hybridization events between formerly isolated species of Eurasia have produced the most common genotype of the second-worst invasive plant species in the United States.