Dr. Christina Caruso
Office: SCIE 1471
Lab: SCIE 1409/1410
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.
BA - Oberlin College
Ph.D. - University of Illinois
I am an evolutionary biologist interested in the mechanisms and causes of natural selection in wild plant populations. My research currently focuses on three projects:
The evolutionary ecology of cytonuclear interactions: Interactions between cytoplasmic and nuclear genomes have significant consequences for the fitness of all eukaryotes. Understanding why the frequency of interacting cytoplasmic and nuclear genes varies among populations is important because these interactions can contribute to the evolution of hybrid incompatibilities. In collaboration with Andrea Case (Kent State University), I am studying the most common cytonuclear interaction in flowering plants, between mitochondrial genes that disrupt pollen production (cytoplasmic male sterility genes (CMS)) and matching nuclear genes that restore it (nuclear male fertility restorers (Rf)). We have been testing the prediction that there is a fitness cost of carrying nuclear male fertility restorers ('cost of restoration'). If this fitness cost prevents restorers from spreading to fixation in some species, then plants will produce either female or hermaphrodite flowers, a breeding system known as gynodioecy. We found that gynodioecious populations with a high cost of restoration contain more female plants, supporting the prediction that this fitness cost is a key determinant of variation in the frequency of nuclear male fertility restorers. We plan to test whether the cost of restoration can also explain the distribution of nuclear male fertility restorers in non-gynodioecious species, and thus whether CMS/Rf incompatibilities contribute to the evolution of reproductive isolation in angiosperms. Funding: US National Science Foundation and the National Evolutionary Synthesis Center
The limits to phenotypic evolution: Some trait combinations evolve repeatedly, while other trait combinations evolve rarely or not at all, suggesting that there are limits on phenotypic evolution. However, these limits are rarely identified. In collaboration with Hafiz Maherali (University of Guelph), I have been using artificial selection to test whether genetic constraints or natural selection limit the joint evolution of photosynthesis and transpiration. We are studying these correlated traits because they are key determinants of growth and reproduction in plants. We found that plants in our selection lines evolved novel combinations of photosynthesis and transpiration, suggesting that the evolution of these traits is not limited by a lack of genetic variation. We now plan to use our selection lines to test whether the evolution of photosynthesis and transpiration is instead limited by natural selection against individuals with novel trait combinations. Funding: NSERC
The causes of natural selection: Although >5000 estimates of natural selection have been published, the biotic and abiotic factors that cause traits to be associated with fitness are often not identified. Identifying these factors is important because the relationship between traits, fitness, and the causes of selection can be used to predict how organisms will adapt to the novel environments they encounter during range expansion or periods of global environmental change. To determine the relative importance of different causes of natural selection and how they interact to affect fitness, I have been estimating selection on floral traits exerted by antagonistic herbivores vs. mutualistic pollinators. We found that seed predators exerted selection on floral traits, suggesting that these traits are in part adaptations to reduce the fitness costs of antagonistic interactions. However, we also found that herbivores and pollinators selected for similar floral traits, suggesting that antagonistic interactions will not constrain adaptation to mutualists. As part of a working group at the National Evolutionary Synthesis Center, I am currently using meta-analyses to extend these conclusions about the relative importance of different causes of natural selection to a wider range of taxa and traits. Funding: NSERC
Caruso, C. M. and A. L. Case. 2013. Testing models of sex ratio evolution in a gynodioecious plant: female frequency covaries with the cost of male fertility restoration. Evolution 67: 561-566.
Caruso, C. M., A. L. Case, and M. F. Bailey. 2012. The evolutionary ecology of cytonuclear interactions in angiosperms. Trends in Plant Science 17: 638-643.
Caruso, C.M. 2012. Sexual dimorphism in floral traits of gynodioecious Lobelia siphilitica L. (Lobeliaceae) is consistent across populations. Botany 90: 1245-1251.
Parachnowitsch, A.L., C.M. Caruso, S. Campbell and A. Kessler. 2012. Lobelia siphilitica plants that escape herbivory in time also have reduced latex production. PLoS ONE 7(5): e37745.
Caruso, C.M., A.M. Benscoter, and H. Maherali. 2012. Why are trade-offs between flower size and number infrequently detected? A test of three hypotheses. International Journal of Plant Sciences 173: 26-36. *Featured Cover Article*.
Donovan, L. A., H. Maherali, C. M. Caruso, H. Huber, and H. de Kroon. 2011 The evolution of the worldwide leaf economics spectrum. Trends in Ecology and Evolution 26: 88-95.
Caruso, C. M., S. L. Scott, J. C. Wray, and C. A. Walsh. 2010. Pollinators, herbivores, and the maintenance of flower color variation: a case study with Lobelia siphilitica. International Journal of Plant Sciences 171: 1020-1028. (Special Issue on Natural Selection in Plant Populations).
Case, A. L. and C. M. Caruso. 2010. A novel approach to estimating the cost of male fertility restoration in gynodioecious plants. New Phytologist 186: 549-557.
Maherali, H., C. M. Caruso, M. E. Sherrard, and R. G. Latta. 2010. Adaptive value and costs of physiological plasticity to soil moisture limitation in recombinant inbred lines of Avena barbata. American Naturalist 175: 211-224.
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.
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
Wassink, Erica (MSc)
Weber, Stefan (MSc)