Research interests

In our research we seek to deepen our understanding of speciation and adaptation by gathering critical genetic data from a variety of species in field and laboratory settings, by developing and applying novel statistical analyses to genetic data, and through the development of theoretical models.

One goal of our research is to understand the genetic architecture of boundaries between species. Geographic contact between previously isolated lineages can lead to their coalescence through introgression, or to the maintenance of derived characteristics in divergent lineages. Part of our work involves identifying the genetic conditions that favor either outcome.

A second and related goal of our research is to contribute to our growing understanding of the genetics of adaptation. We are developing statistical genetics methods for use in this area. We're also interested in the use of natural hybrid zones for mapping genes underlying adaptive phenotypes and components of isolation between taxa.

Below is a description of some of the research projects that Alex Buerkle participates in or leads. Additional projects are described on the webpages of individual members of the lab.

Genetic architecture of species boundaries

Barriers to gene flow allow discrete groups of organisms, such as species, to persist. In many cases reproductive barriers between taxa are incomplete and hybridization occurs in zones of geographic contact. A central focus of our research is to understand how different genetic architectures influence the fate of hybridizing taxa, and includes studies of the origin of diploid species through hybridization.

Examples of research projects include:

1. Zach Gompert (Ph.D. student) and I work on statistical models for mapping components of reproductive isolation and adaptive introgression (Gompert and Buerkle 2009a). This builds on methods development for the analysis of Populus hybrid zones (Lexer et al. 2007) and earlier research (Buerkle and Rieseberg 2001, Rieseberg and Buerkle 2002). We have developed software that implements our approach (introgress, Gompert and Buerkle 2009b) and continue to maintain stand-alone software for quantifying the genetic composition of hybrids (hindex, Buerkle 2005). In collaborative projects we have examined the genetics of isolation in a variety of taxa (e.g., sculpins, Nolte et al. 2009; mouse, Teeter et al. 2010).

2. 

   I have modeled the ecological and genetic conditions that affect the origin of species through hybridization, and specifically hybrid species that have arisen without an increase in ploidy (Buerkle et al. 2000). We also modeled the risk of extinction through hybridization (Buerkle et al. 2003).

   In a related study, we used genetic maps from three hybrid species of sunflowers and junction theory to infer the rate of genome stabilization that followed diploid hybrid speciation (Buerkle and Rieseberg 2008).

Genetics of adaptation

Variation at molecular markers makes it possible to study of specific genomic regions contributing to the expression of quantitative traits and allows an analysis of the genetic basis of adaptation and speciation at multiple levels of resolution (e.g., quantitative trait loci, candidate genes). My initial involvement in this area was as a collaborator on a study of the genetics of divergent skeletal and trophic morphologies in two species of threespine sticklebacks (Peichel et al. 2001).

Examples of research projects include:

1. Hybrid zones contain naturally recombinant individuals that may be used for genetic mapping (Rieseberg and Buerkle 2002, Buerkle and Lexer 2008). We continue to develop methods for mapping quantitative traits and identifying regions of the genome under selection in natural hybrid zones. In a collaboration with Christian Lexer and other colleagues who work with Populus, and with Zach Gompert, we have made some more progress in developing tools to identify genome regions under divergent selection in hybridizing species (Lexer et al. 2007, Gompert and Buerkle 2009a), including software that implements our approach (introgress, Gompert and Buerkle 2009b).

   Qiurong Wang (Ph.D. student) has developed a method for inferring a linkage map from recombinant individuals in a hybrid zone. Qiurong is also working on reconstructing the history of recombination among strains of laboratory mice.

2. Monia Haselhorst (Ph.D. student) has begun research on hybridization in North American spruce with the goal of using recombinant individuals to study the basis adaptive ecophysiological variation between taxa.

3. Tom Parchman (postdoctoral researcher) is studying lodgepole pine population structure and will use association mapping to dissect the genetics of serotiny.

Selected publications

Teeter, K. C., L. M. Thibodeau, Z. Gompert, C. A. Buerkle, M. W. Nachman, and P. K. Tucker. in press. The variable genomic architecture of isolation between hybridizing species of house mice. Evolution (article).

Gompert, Z. and C. A. Buerkle. 2009b. introgress: a software package for mapping components of isolation in hybrids. Molecular Ecology Resources (article).

Nolte, A. W., Z. Gompert, and C. A. Buerkle. 2009. Variable patterns of introgression in two sculpin hybrid zones suggest that genomic isolation differs among populations. Molecular Ecology 18: 2615-2627 (article).

Buerkle, C. A.. 2009. Ecological context shapes hybridization dynamics. Molecular Ecology 18: 2077-2079 (article).

Gompert, Z. and C. A. Buerkle. 2009a. A powerful regression-based method for admixture mapping of isolation across the genome of hybrids. Molecular Ecology 18: 1207-1224 (article).

Buerkle, C. A. and C. Lexer. 2008. Admixture as the basis for genetic mapping. TREE 23: 686-694. (article)

Buerkle, C. A. and L. H. Rieseberg. 2008. The rate of genome stabilization in homoploid hybrid species. Evolution 62: 266-275. (article)

Lexer, C., C. A. Buerkle, J. A. Joseph, B. Heinze, and M. F. Fay. 2007. Admixture in European Populus hybrid zones makes feasible the mapping of loci that contribute to reproductive isolation and trait differences. Heredity 98: 74-84. (article)

Buerkle, C. A. 2005. Maximum-likelihood estimation of a hybrid index based on molecular markers. Molecular Ecology Notes 5: 684-687. (article)

Buerkle, C. A., D. E. Wolf, and L. H. Rieseberg. 2003. The origin and extinction of species through hybridization. in Population Viability in Plants: Conservation, Management, and Modeling of Rare Plants, pp. 117-141. Springer Verlag.

Rieseberg, L. H., and C. A. Buerkle. 2002. Genetic mapping in hybrid zones. American Naturalist 159: S36-S50. (article)

Peichel, C. L., K. Nereng, K. A. Ohgi, B. L. E. Cole, P. F. Colosimo, C. A. Buerkle, D. Schluter, and D. M. Kingsley. 2001. The genetic architecture of divergence between threespine stickleback species. Nature 414: 901-905. (article)

Buerkle, C. A., and L. H. Rieseberg. 2001. Low intraspecific variation for genomic isolation between hybridizing sunflower species. Evolution 55: 684-691. (article)

Buerkle, C. A., R. J. Morris, M. A. Asmussen, and L. H. Rieseberg. 2000. The likelihood of homoploid hybrid speciation. Heredity 84: 441-451. (article)