My research interests encompass areas of plant systematics and evolutionary biology, and I use both comparative and experimental approaches for tackling specific questions. The particular groups that I study are agamic complexes in the sunflower family. In these groups, hybridization, polyploidy, and asexual reproduction through seeds (apomixis) combine to produce an array of populations with complex interrelationships. I am attempting to understand the evolutionary dynamics that produce and maintain variation in these groups using molecular phylogenetic and population genetic approaches. Among the questions that I am interested in are the following:

How genetically variable are polyploid asexual populations?
Individuals within populations may represent clones of a single maternal founder, clones from multiple founders, or via occasional asexual reproduction, they may have more complex relationships. The ability of these populations to generate new variants plays a major role in determining their ability to persist over time.

What are the factors that affect the balance between sexual and asexual reproduction?
Both genetic and environmental factors contribute to the balance between sexual and asexual reproduction in polyploids in agamic complexes. Through experimental manipulations and with the use of genetic markers, I hope to further our understanding of genetic and environmental factors that affect this balance.

WE ARE CURRENTLY ADDRESSING THESE QUESTIONS IN TWO STUDY SYSTEMS:

The North American Crepis agamic complex (Lactuceae: Asteraceae)

This group is the subject of a classical study by E. B. Babcock and G. L. Stebbins (1938. Carnegie Inst. Washington Publ. No. 504) on patterns of morphological and chromosome number variation in an agamic complex. This work forms much of the basis of our understanding of these groups.

Members of the complex are broadly distributed in western North America. The diploids typically have more restricted geographical ranges than the polyploid, and occur under a wider variety of environmental conditions.

The complex is based upon seven diploid species (Crepis acuminata, C. atribarba, C. bakeri, C. modocensis, C. monticola, C. occidentalis and C. pleurocarpa) and innumerable polyploid derivatives, classified taxonomically either under the species name of the diploid they most closely resemble, or into one of two species (C. barbigera, C. intermedia), that are known only as polyploids, but are morphologically distinct from known diploids. In reality, particular polyploid populations can be very difficult to assign to species, because they may combine the morphological features of two or more taxa.

Analysis of chloroplast DNA variation in populations from throughout the range of the complex revels that the most common species; based on morphological criteria, have multiple chloroplast DNA haplotypes, and that shared morphology does not imply shared ancestry. Current work is aimed at analysis of levels of variation within populations, which we will use to infer whether or not populations retain residual sexuality.

Townsendia (Astereae: Asteraceae)

The genus Townsendia comprises about 25 species of mostly perennial herbs native to western North America. This agamic complex includes sexual diploid and apomictic tetraploid members. Our work on this system is just beginning. Our first objective is to examine phylogenetic relationships among diploid and polyploid members of the genus, using nucleotide sequence variation. The phylogeny will provide the framework for further experimental and comparative studies in the genus.

N. Rajakaruna and J. Whitton, J. (2004). Trends in the evolution of edaphic specialists with an example of parallel evolution in the Lasthenia californica complex. In Q.C.B. Cronk, R. Ree, I.E.P Taylor and J. Whitton. Plant Adaptation: Ecology and Molecular Biology (In Press).

Rajakaruna, N., M.Y. Siddiqi, J. Whitton, B.A. Bohm & A.D.M. Glass. 2003. Differential responses to Na+/K+ and Ca2+/Mg2+ in two edaphic races in the Lasthenia californica complex (Asteraceae). New Phytologist 157: 93-103. (pdf)

Rajakaruna, N., G.E. Bradfield, B.A. Bohm and J. Whitton. 2003. Adaptive differentiation in response to water stress by edaphic races of Lasthenia californica (Asteraceae). International Journal of Plant Sciences 164: 371-376. (pdf)

Rajakaruna, N., B.G. Baldwin, R. Chan, A.M. Desrochers, B.A. Bohm and J. Whitton. 2003. Edaphic races and phylogenetic taxa in the Lasthenia californica complex (Asteraceae: Heliantheae): an hypothesis of parallel evolution. Molecular Ecology 12: 1675-1679. (pdf)

Rundle, H.D., F. Breden, C. Griswold, A.Ø. Mooers, R.A. Vos and J. Whitton. 2001. Hybridization without Guilt: Gene Flow and the Biological Species Concept. Journal of Evolutionary Biology 14: 868-869. (pdf)

Otto, S. P. and J. Whitton. 2000. Polyploid Incidence and Evolution. Annual Review of Genetics 34: 401-437. (pdf)

Whitton, J. and N. Rajakaruna 2000. Plant Biodiversity. Encyclopedia of Biodiversity, Academic Press. Invited contribution.

Gardner, K. , A. Buerkle, J. Whitton, and L. H. Rieseberg. 2000. Inferring epistasis in wild sunflower hybrid zones. Pp. 264-279 In J.B. Wolf, E.D. Brodie III and M.J. Wade, eds. Epistasis and the Evolutionary Process. Oxford University press, Oxford.

Holsinger, K. E., R. J. Mason-Gamer, and J. Whitton. 1999. Genes, demes and plant conservation. Pp. 23-46 In L. F. Landweber and A. P. Dobson, eds. Genetics and the extinction of species. Princeton University Press, Princeton, New Jersey.

Rieseberg, L. H., J. Whitton, and K. Gardner. 1999. Hybrid zones and the genetic architecture of a barrier to gene flow between two sunflower species. Genetics 152: 713-727.

Whitton, J., D. E. Wolf, D. M. Arias, A. A. Snow, and L. H. Rieseberg. 1997. The persistence of cultivar alleles in wild populations of sunflowers five generations after hybridization. Theoretical and Applied Genetics 95: 33-40.

Whitton, J., L. H. Rieseberg, and M. C. Ungerer. 1997. Microsatellite loci are not conserved across the Asteraceae. Molecular Biology and Evolution 14: 204-209.

Rieseberg, L. H., J. Whitton, and C. R. Linder. 1996. Molecular marker incongruence in plant hybrid zones and phylogenetic trees. Acta Botanica Neerlandica 45: 243-262. (pdf)

Whitton, J., R. S. Wallace, and R. K. Jansen. 1995. Phylogenetic relationships and patterns of character change in the tribe Lactuceae (Asteraceae) based on chloroplast DNA restriction site variation. Canadian Journal of Botany 73: 1058-1073.

Pigliucci, M., J. Whitton, and C. D. Schlichting. 1995. Reaction norms of Arabidopsis. I. Plasticity of characters and correlations across water, nutrient and light gradients. Journal of Evolutionary Biology 8: 421-438. (pdf)

Pigliucci, M., C. D. Schlichting, and J. Whitton. 1995. Reaction norms of Arabidopsis. II. Response to stress and unordered environmental variation. Functional Ecology 9: 537-547. (pdf)

Bain, J. F. and J. Whitton. 1994. Taxonomic analysis of Senecio pauciflorus and S. indecorus (Asteraceae). Nordic Journal of Botany 14: 193-199.

Whitton, J. and J. F. Bain. 1992. An analysis of morphological variation in Senecio cymbalaria Pursh. Canadian Journal of Botany 70: 285-290.

In Preparation:

Cronk, Q.C.B., R. Ree, I.E.P. Taylor and J. Whitton (Eds.). 2004. Plant Adaptation: Ecology and Molecular Biology.