- Ph.D., The University of Michigan, 1978
- M.S., University of Michigan, 1976
- B.A., Miami University (Ohio), 1973
Ecology and Evolution of Plant Reproduction
Because pollen performance (germination, tube growth rates, and the ability to achieve fertilization) directly affects the transmission of genes from one generation to the next, an understanding of the factors affecting pollen performance is fundamental to evolutionary biology, while the ability to manipulate pollen performance has profound implications for the applied plant sciences and biotechnology. Historically, my research program’s major goals have been to identify which of the population of pollen grains deposited onto a stigma achieve fertilization, to determine the genetic and environmental factors responsible for differences in pollen performance, to determine if selection can act at the level of the microgametophyte, and to identify the consequences of microgametophyte selection on the resulting progeny.
Over the past 25 years, we have studied the effects of growing conditions (soil nutrients, mycorrhizal infection levels, and herbivory) on the number, size, chemical composition, and performance of pollen; the causes and consequences of an age-dependent breakdown in self-incompatibility in Campanula rapunculoides and Solanum carolinense; the effects of inbreeding on pollen performance; and in vivo pollen selection for tolerance to high temperatures. Our experimental approaches to these problems range from greenhouse and garden studies employing quantitative genetic designs through the use of morphological, biochemical, and molecular genetic markers to the deployment of a variety of physiological, developmental, and molecular techniques.
Effects of Inbreeding on Herbivory and Disease Dynamics
Our recent research focuses on the role of inbreeding and genetic variation on herbivory and the establishment and transmission of plant diseases. This research has three interrelated themes. First, we study the interrelationships among inbreeding, herbivory, and transmission of bacterial and viral diseases vectored by herbivores. We examine how inbreeding affects the pattern, timing, and magnitude of herbivory; the rates of exposure to pathogens transmitted by herbivores; and when—and the extent to which—plant defense systems respond to herbivores and pathogens. Second, we study the production of volatile organic compounds that signal herbivores (pathogen vectors). We examine how plant volatiles vary with inbreeding in natural populations and how herbivores respond to these differences; how the composition of plant volatiles changes upon damage by an herbivore or infection by a pathogen; and whether or not herbivores/vectors respond differently to the volatile compounds produced by healthy and diseased plants. Finally, we study the impact of the escape of viral resistance transgenes from agricultural crops to wild populations. We examine how viral resistance transgenes affect the fitness of plants during introgression into natural populations; whether or not there is a cost associated with viral resistance transgenes when the viral disease is not present in the population; and how viral resistance transgenes affect non-target pathogens. These studies employ a variety of biochemical, immunological, and molecular techniques including GC/MS, quantitative rt-PCR, GFP transformations, DAS-ELISA, microarrays, and Sanger and Next Generation sequencing, in addition to greenhouse and field experiments employing quantitative genetic designs.
(2011 - 2012)
Simmons, H.E., E.C. Holmes, A.G. Stephenson. 2011. Rapid turnover of intra-host genetic diversity in zucchini yellow mosaic virus. Virus Research 155:389-396.
Simmons, H.E., E.C. Holmes, F.E. Gildow, M.A. Bothe-Goralczyk, and A.G. Stephenson. 2011. Experimental verification of seed transmission in zucchini yellow mosaic virus. Plant Disease 95:751-754.
Kariyat, R.R., S.C. Scanlon, M.C. Mescher, C.M. De Moraes and A.G. Stephenson. 2011. Inbreeding depression in Solanum carolinense (Solanaceae) under field conditions and implications for mating system evolution. PLoS One 6(12): e28459. doi:10.1371/journal.pone.0028459.
Stephenson, A.G. 2012. Safe sex in plants. New Phytologist 193:827-829.
Kariyat, R.R., K.E. Mauck, C.M. De Moraes, A.G. Stephenson and M.C. Mescher. 2012. Inbreeding alters volatile signaling phenotypes and influences tri-trophic interactions in horsenettle (Solanum carolinense L). Ecology Letters 15: 301–309. DOI: 10.1111/j.1461-0248.2011.01738.x
Kariyat, R.R., J.I. Mena-Ali, B. Forry, M.C. Mescher, C.M. De Moraes and A.G. Stephenson. In press. Inbreeding, herbivory and the transcriptome of Solanum carolinense L. Entomol. Expt. Appl.