Dr. Christina Caruso
Assistant Professor

Email: carusoc@uoguelph.ca

Office: SCIE 1471
Ext: 52030
Lab: SCIE 1409/1410
Ext: 56014

Profile

My research focuses on the role of natural selection in driving phenotypic diversification and speciation in natural populations. Although biologists since Darwin have postulated that natural selection is an important mechanism promoting the evolution of diversity, fundamental questions such as how much selection varies in time and space, the ecological causes of selection, and the genetic basis of selected traits remain unanswered. I first studied these topics as an undergraduate at Oberlin College, where I did field work on plants, amphibians, and mammals. My fascination with ecology and evolutionary biology led me to the University of Illinois, where I completed my doctoral dissertation on the role of interspecific competition for pollinators in driving floral evolution. During this time, I became interested in understanding the genetic basis of complex traits, such as flowers, that have been shaped by natural selection. This motivated me to study the quantitative genetics of natural variation in plant floral and physiological traits as a postdoctoral fellow at Grinnell College and Duke University. I am continuing this research in ecology, evolution, and genetics in the Department of Integrative Biology at the University of Guelph.

Education

BA - Oberlin College
Ph.D. - University of Illinois

Research

My research has included work on the effect of competition on floral evolution (e.g. Caruso 2000 in Evolution), the potential for genetic constraints on adaptive evolution (e.g. Caruso 2004, Caruso et al. 2005, both in Evolution), the adaptive value of plasticity in plant physiological traits (e.g. Caruso et al. 2006 in Evolution, Maherali et al. in press at American Naturalist) and the evolution of gender and sexual dimorphism in plants (e.g. Caruso & Case 2007, Caruso & Yakobowski 2008, both in Journal of Evolutionary Biology). The common thread linking these diverse projects is my interest in the process of evolution by natural selection. Natural selection is the only mechanism that can cause adaptation, the evolution of traits that enhance reproduction and survival. Although Darwin proposed the mechanism of natural selection 150 years ago, most estimates of selection have been made in the last 25 years. Consequently, we are only now in the position to answer many longstanding questions about the causes and consequences of natural selection in the wild. Current work in my lab focuses on three of these questions.

Sex ratio evolution in plants-The sex ratio has important implications for the population dynamics and evolution of all organisms with separate sexes because it affects the number of available mates. In collaboration with Andrea Case (Kent State University), I am determining the contributions of natural selection vs. other evolutionary mechanisms to variation in population sex ratio of the gynodioecious plant Lobelia siphilitica. Lobelia siphilitica plants produce either pistillate (containing ovules) or perfect (containing ovules and pollen) flowers, and the proportion of female plants varies widely among populations. Models predict that differences in fitness between hermaphrodite genotypes, a mechanism of selection known as the cost of restoration, is a key determinant of variation in population sex ratios. By using a novel approach to estimating the cost of male fertility restoration, we will provide the first test of this prediction in natural populations. We will also use molecular tools to test the alternative hypothesis that variation in population sex ratios is largely determined by metapopulation forces such as founder effects and gene flow. Funding: US National Science Foundation

The roles of selection vs. constraint in the evolution of complex traits-Correlations among functionally related traits are ubiquitous in both plants and animals. These correlations could be the result of genetic integration, which prevents the production of unfit trait combinations. Alternatively, natural selection against unfit trait combinations could maintain correlations in the absence of any genetic integration. To distinguish between these two hypotheses, I am collaborating with Hafiz Maherali (University of Guelph) on a study of the roles of selection vs. constraint in maintaining the correlation between photosynthesis and transpiration, two key determinants of growth and reproduction in plants. Phenotypic correlations between photosynthesis and transpiration are strong and positive because stomata must be open to allow CO2 to diffuse into leaves, but water is lost by transpiration via these same pores. We are using artificial selection to test whether the correlation between these traits in Lobelia siphilitica is the result of genetic integration. The selection lines will then be used to test whether the phenotypic correlation between these traits is maintained by natural selection. If genetic integration, rather than natural selection, is maintaining the correlation between photosynthesis and transpiration, then evolution in response to selection for novel combinations of these traits may be constrained. Funding: NSERC Discovery

Dissecting the ecological causes of selection on floral traits-Biologists since Darwin have assumed that floral traits are primarily adaptations to enhance pollination. However, antagonists such as herbivores may also exert selection these traits. If so, then many floral traits may be adaptations to reduce herbivory rather than to enhance pollination. My undergraduate and graduate students are characterizing the importance of selection exerted by antagonistic herbivores vs. mutualistic pollinators in shaping the evolution of floral traits in Lobelia siphilitica. In particular, we are testing whether pollinators and herbivores exert diffuse or pairwise selection on floral traits. If much of the selection on these traits is diffuse, then co-adaptation between plants and their pollinators will be constrained when herbivores are present. Alternatively, if much of the selection is pairwise, then co-adaptation between plants and pollinators will be possible even when plants are also interacting with herbivores. Funding: NSERC Discovery

Selected Publications

Maherali, H., C. M. Caruso, M. E. Sherrard, and R. G. Latta. Adaptive value and costs of physiological plasticity to soil moisture limitation in recombinant inbred lines of Avena barbata. In Press at American Naturalist

Maherali, H., C. M. Caruso, and M. E. Sherrard. 2009. The adaptive significance of ontogenetic changes in physiology: a test with Avena barbata. New Phytologist 183:908-918. (Included in Special Issue "Plant adaptation-following in Darwin's footsteps").

Caruso, C. M. and S. J. Yakobowski. 2008. Selection on floral and carbon uptake traits of Lobelia siphilitica in similar in females and hermaphrodites. Journal of Evolutionary Biology 21: 1514-1523.

Parachnowitsch, A. L. and C. M. Caruso. 2008. Predispersal seed herbivores, not pollinators, exert selection on floral traits of Lobelia siphilitica. Ecology 89: 1802-1810.

Caruso, C. M. and A. L. Case. 2007. Sex-ratio variation in gynodioecious Lobelia siphilitica: effects of population size and geographic location. Journal of Evolutionary Biology 20: 1396-1405.

Caruso, C. M., H. Maherali, and M. E. Sherrard. 2006. Plasticity of physiological traits in Lobelia: testing for adaptation and constraint. Evolution 60: 980-990.

Caruso, C. M., H. Maherali, A. Mikulyuk, K. Carlson, and R. B. Jackson. 2005. Genetic variance and covariance for physiological traits in Lobelia: are there constraints on adaptive evolution? Evolution 59: 826-837.

Caruso, C. M. 2004. The quantitative genetics of floral trait variation in Lobelia: potential constraints on adaptive evolution. Evolution 58: 732-740.

Caruso, C. M. 2002. Influence of plant abundance on pollination and selection on floral traits of Ipomopsis aggregata. Ecology 83: 241-254.

Caruso, C. M. 2000. Competition for pollination influences selection on floral traits of Ipomopsis aggregata. Evolution 54: 1546-1557.

Teaching

BIOL*2250 - Biostatistics and the Life Sciences
BIOL*3110 - Population Ecology
BOT*2050 - Plant Ecology
BOT*3710 - Plant Diversity and Evolution
UNIV*1200 - Darwin's Dangerous Idea

Grad Students

Walsh, Catherine (MSc)
Weber, Stefan (MSc)