Biochemistry
R. Bentley
J. Brodsky
J. Franzen
P. Grabowski
J. Hempel
L. Jen-Jacobson
K. Kiselyov
C. Peebles
J. Rosenberg
A. Schwacha

Cell Biology
J. Brodsky
A. Chung
J. Hildebrand
L. Jacobson
N. Kaufmann
K. Kiselyov
J. Pipas
M.-T. Sáens-Robles
W. Saunders
C. Walsh

Computational Biology
M. Grabe
J. Lawrence
J. Rosenberg

Developmental Biology
G. Campbell
D. Chapman
J. Hildebrand
B. Roman
S. Shostak
B. Stronach
V. Twombly

Ecology
T.-L. Ashman
W. Carson
W. Coffman
S. Kalisz
T. Katzner
R. Relyea
S. Tonsor
B. Traw

Evolution
T.-L. Ashman
A. Bledsoe
S. Kalisz
J. Lawrence
Z.-X. Luo
R. Relyea
S. Shostak
S. Tonsor
B. Traw

Genetics
K. Arndt
T.-L. Ashman
G. Campbell
D. Chapman
G. Hatfull
J. Hildebrand
L. Jacobson
S. Kalisz
J. Martens
V. Oke
W. Saunders
B. Stronach
S. Tonsor
R. Wood

Microbiology
G. Hatfull
R. Hendrix
J. Lawrence
V. Oke
J. Pipas
M. Popa
I. Campbell
R.L. Duda
S. Godfrey

Molecular Biology
K. Arndt
J. Franzen
P. Grabowski
G. Hatfull
R. Hendrix
L. Jen-Jacobson
J. Martens
C. Peebles
J. Pipas
J. Rosenberg
A. Schwacha
C. Walsh

Plant Biology
T.-L. Ashman
W. Carson
S. Kalisz
V. Oke
C. Partanen
S. Tonsor
B. Traw

Science Education
A. Bledsoe
K. Curto
L. Daniels
S. Godfrey
N. Kaufmann
C. LaFave
J. Newman
E. Polinko
M. Popa
L. Roberts
T. Seiflein
R. Sherwin
A. Slinskey Legg

Structural Biology
M. Grabe
J. Hempel
R. Hendrix
L. Jen-Jacobson
J. Rosenberg
A. VanDemark

Former Faculty

Professional Interests - Publications - Contact Information - Lab Personnel

Professional Interests of Stephen Tonsor

The adaptive evolution of the phenotype is the result of a complicated set of nested interactions- the interactions of genes in development, of genes with environment, of genotypes with each other through shared environments and systems of mating, and of populations through the dispersal of gametes and seeds. Work in my laboratory is aimed towards understanding the role of these interactions in evolution. We work with flowering plants. Work has mainly focussed on four levels of interactions:

1. Interactions at the population level - Effects of dispersal and mating system on population genetic structure
2. Interactions between genes in a population context - Epistatic interactions, population genetic structure and evolution
3. Interaction between genes and the environment - The lability of genetic architecture in changing environments (his is the current central focus of the lab)
4. Ecological interactions between genotypes -The physiological genetic basis of competitive ability

(1) Dispersal, mating system and selection: The development of population genetic structure

Although there are a great many published studies of population genetic structure, there are only a handful in which the causes of structuring can be inferred. In particular, mating system and dispersal are often assumed to be the causes of structure, whereas selection, either spatially variable selection or selection on heterozygosity, can also explain patterns of spatial structure and deviations from expected heterozygosity levels, respectively. One useful tool for distinguishing between the effects of mating system, dispersal and selection is to simultaneously determine genotype and life history stage/age. We did this in a weedy angiosperm, Plantago lanceolata, and found that the patterns produced by early life history events (mating system and dispersal) were not evident in later life history stages. Instead, spatial structure (as F_ST) developed between the seed and adult stages. In addition, the excess homozygosity in evidence at the seed stage was replaced by excess heterozygosity among reproductive plants (F_IS went from positive to negative) (Tonsor, Kalisz, Fisher and Holtsford 1993).

In a second study of stage-classified population genetic structure, this one in the native wildflower Trillium grandiflorum, we found a similar pattern in that spatial genetic structure was undetectable at the seedling stage but highly significant at the reproductive stage (measured by spatial autocorrelation) (Kalisz, Nason, Hanzawa and Tonsor, in review).

In both these studies, one cannot distinguish between historical effects influencing the differences between life history stages. Our next step is to re-assay these populations over the next two years, asking if the differences in spatial structure among life history stages represent differences in disturbance/dispersal history among life history stages, or a general pattern of changing population spatial structure associate with development in each of these species.

(2) Epistatic interactions, population genetic structure and evolution

Epistatic interactions can allow complex evolutionary dynamics which do not occur with simpler genetic systems (Whitlock, Phillips, Moore and Tonsor, 1995). We have explored the geographic scale at which alternative sets of interacting genes can be maintained in Plantago lanceolata. This question is central to understanding population divergence, speciation and Sewall Wright's shifting balance process. We examined genetic neighborhoods within populations (Tonsor and Goodnight, 1997) and are completing work on small populations within a metapopulation.

We have also been using computer simulations to examine the shifting balance process, and its role in the spatial pattern of variation for interacting genes. The simulations show that Wright's shifting balance occurs under a very limited range of migration rates (Moore and Tonsor, 1994), but its likelihood increases as the number of interacting loci increases (Moore and Tonsor, in revision), and as migration rates are allowed to fluctuate over evolutionary time scales (Moore, unpublished).

(3) The lability of genetic architecture in changing environments

We are exploring the potential for adaptive evolution in response to elevated atmospheric CO₂, and the physiological basis of that variation (Curtis et al., 1995; Klus et al., in press). Fifteen homozygous genotypes of Arabidopsis thalliana from 15 locations world-wide differ in their responses to elevated CO₂ in total growth, allocation and life history shifts. In addition, the phenotypic variances and co-variances among these traits within environments shift as the environment shifts, and the phenotypic covariances in some traits change across environments. The genetic variance in many of these traits shows marked shifts across environments as well (Tonsor et. al, in preparation). We interpret these results as demonstrating that novel environments can lead to novel genetic architectures. We are currently comparing genetic variances and covariances among traits and across CO₂ environments in Arabidopsis thalliana, with 34 genotypes and five CO₂ environments which range from pre-industrial to 3X current ambient levels. Traits examined include mass and its partitioning, Nitrogen content and its partitioning among mass components, dissolved sugar, glucosinilate and starch content by mass component, photosynthetic rates and photosynthetic electron transport rates. In 2001, we will begin work identifying the genetic loci responsible for the observed variation through quatitative trait localization (QTL), and quantifying the magnitute of QTL contributions to phenotypic variation as a function of CO₂environment.

(4) The physiological genetic basis of competitive ability

Using genotypes of Arabidopsis thalliana which differ in nitrogen and carbon uptake rates and use efficiencies, as demonstrated in project #3 above, we are exploring the extent to which Tilman's R* model explains competitive outcome in experimental 2-genotype populations. In a fully factorial design, we are competing three genotypes as both focal plant and competitor, in high and low levels of light and nitrogen.

Publication Archive
22 Citations
14 Abstracts
12 PDFs

Recent Publications of Stephen Tonsor

Paul, J.R., and S.J. Tonsor (2008) Explaining geographic range size by species age: a test using Neotropical Piper species. Pp 46-62 in Tropical Forest Community Ecology, Carson, W.P., and S. Schnitzer, Ed. Blackwell Publishing, Oxford

Tonsor, S.J., C. Scott, I. Boumaza, T.R. Liss, J.L. Brodsky, and E. Vierling (2008) Heat shock protein 101 effects in A. thaliana: genetic variation, fitness and pleiotropy in controlled temperature conditions. Mol. Ecol. 17:1614-1626 (PDF Reprint: 717 kb)

Majetic, C.J., R.A. Raguso, S.J. Tonsor, and T.-L. Ashman (2007) Flower color-flower scent associations in polymorphic Hesperis matronalis (Brassicaceae). Phytochemistry 68:865-874

Tonsor, S.J., and S.M. Scheiner (2007) Plastic trait integration across a CO₂ gradient in Arabidopsis thaliana. Am. Nat. 169:E119-E140

Tonsor, S.J., C. Alonso-Blanco, and M. Koornneef (2005) Gene function beyond the single trait: natural variation, gene effects, and evolutionary ecology in Arabidopsis thaliana. Plant Cell Environ. 28:2-20 (PDF Reprint: 205 kb)

Jenkins-Klus, D., S. Kalisz, P.S. Curtis, J.A. Teeri, and S.J. Tonsor (2001) Family- and population-level responses to atmospheric CO₂ concentration: gas exchange and the allocation of C, N, and biomass in Plantago lanceolata (Plantaginaceae). Am. J. Bot. 88:1080-1087 (PDF Reprint: 99 kb)

Kalisz, S., J. Nason, F.M. Hanzawa, and S.J. Tonsor (2001) Spatial population genetic structure in Trillium grandiflorum: the roles of dispersal, mating, history and selection. Evolution 55:1560-1568 (PDF Reprint: 147 kb)

How to Contact Stephen Tonsor

 
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