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Andrew G. Stephenson
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Andrew G. Stephenson

Distinguished Professor of Biology and Associat Dean for Research and Graduate Education

315 Mueller
Phone: 863-1553
Lab Address: 316 Mueller
Lab Phone: 863-4705
Lab: http://www.bio.psu.edu/People/Faculty/Stephenson/Lab/
Email:

Education:

  1. Ph.D., The University of Michigan, 1978
  2. M.S., University of Michigan, 1976
  3. B.A., Miami University (Ohio), 1973

Honors and Awards:

  1. Distinguished Professor of Biology. 2011. The Pennsylvania State University
  2. Howard B. Palmer Faculty Mentoring Award, 2008. The Pennsylvania State University
  3. Roger E. Wilson Memorial Lectures, 2006. Department of Botany, Miami University, Oxford, Ohio
  4. Faculty Scholars Medal for the Life and Health Sciences 2002, The Pennsylvania State University
  5. Current Contents®ISI® Most Highly Cited Researcher (Ecology/ Environmental Science); Biography posted March 2003.
  6. Faculty Associates Award for Outstanding Involvement in Undergraduate Research, 1997, The Pennsylvania State University
  7. Edward D. Bellis Award for Outstanding Contributions to Graduate Education, Intercollege Graduate Program in Ecology, The Pennsylvania State University 1996
  8. Elected Visiting Waynflete Fellow, Magdalen College, University of Oxford, England 1994-1995
  9. George W. Atherton Award for Excellence in Teaching, The Pennsylvania State University 1992
  10. Distinguished Lecturer, Linnaeus Institute for Systematic Botany, University of Uppsala, Uppsala, Sweden 1990
  11. International Agricultural Centre Fellowship, Wageningen, The Netherlands. 1987
  12. Outstanding Teaching Assistant Award, University of Michigan. 1976-1977
  13. J. Fisher and Margaret Stanfield Scholarship for the Outstanding Senior Botany Major, Miami University. 1972-1973

Research Interests:

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, determine the genetic and environmental factors responsible for differences in pollen performance, determine if selection can act at the level of the microgametophyte, and 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

1) Interrelationships among inbreeding, herbivory, and transmission of bacterial and viral diseases vectored by herbivores

How does inbreeding affect:

  • The pattern, timing and magnitude of herbivory?
  • Rates of exposure to pathogens transmitted by herbivores?
  • When — and the extent to which — plant defense systems respond to herbivores and pathogens?

2) Production of volatile organic compounds that signal herbivores (pathogen vectors)

  • How do plant volatiles vary with inbreeding in natural populations? How do herbivores respond to these differences?
  • How does the composition of plant volatiles change upon damage by an herbivore or infection by a pathogen?
  • Do herbivores/vectors respond differently to the volatile compounds produced by healthy and diseased plants?

3) Impact of the escape of viral resistance transgenes from agricultural crops to wild populations

  • How do viral resistance transgenes affect the fitness of plants during introgression into natural populations?
  • Is there a cost associated with viral resistance transgenes when the viral disease is not present in the population?
  • How do viral resistance transgenes affect non-target pathogens?

These studies employ a variety of biochemical, immunological and molecular techniques including GC/MS, quantitatiive rt-PCR, GFP transformations, DAS-ELISA, microarrays, Sanger and Next Generation sequencing, in addition to greenhouse and field experiments employing quantitative genetic designs.

Selected Publications:

  • Simmons, H.E., E.C. Holmes, F.E. Gildow, M.A. Bothe-Goralczyk, and A.G. Stephenson. In press. Experimental verification of seed transmission in zucchini yellow mosaic virus. Plant Disease

  • 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.

  • Stephenson, A.G., L. Shapiro, M.A. Sasu, C.M. DeMoraes and M.C. Mescher. 2010. Factors that influence exposure rates and transmission of Erwinia tracheiphila in Cucurbita pepo. In: Cucurbitaceae 2010, J.A. Thies (ed.). North Carolina State University Press, Raleigh, NC. Pp. 189-193.

  • Sasu, M.A., M.J. Ferrari and A.G. Stephenson. 2010. Inter-relationships among a virus resistance transgene, herbivory, and a bacterial disease in wild Cucurbita. International Journal of Plant Sciences 171:1048–1058. DOI: 10.1086/656531 

  • Sasu, M.A., K.L. Wall, and A.G. Stephenson. 2010. Antimicrobial nectar inhibits a floral transmitted pathogen of a wild Cucurbita pepo (Cucurbitaceae). American Journal of Botany 97:1025-1030. doi:10.3732/ajb.0900381

  • Sasu, M.A., I. Seidl-Adams, K. Wall, J. A. Winsor and A. G. Stephenson. 2010. Floral Transmission of Erwinia tracheiphila by Cucumber Beetles in a Wild Cucurbita pepo. Environmental Entomology 39:140-148.

  • Sasu, M.A., M.J. Ferrari, D. Du, J.A. Winsor and A.G. Stephenson. 2009. Indirect costs of a non-target pathogen mitigate the direct benefits of a virus resistant transgene in wild Cucubita. Proceedings of the National Academy of Science (USA). 106: 19067-19071. www.pnas.org_cgi_doi_10.1073_pnas.0905106106

  • Valdivia, E.R., A.G. Stephenson, D. M. Durachko and D.J. Cosgrove. 2009. Class B β-expansins are needed for pollen separation and stigma penetration. Sexual Plant Reproduction.22:141-152. DOI 10.1007/s00497-009-0099-y

  • Mena-Ali, L. Keser and A.G. Stephenson. 2009. The effect of sheltered load on growth and reproduction in Solanum carolinense, a species with variable self-incompatibility. Sexual Plant Reproduction. 22:63-71 DOI 10.1007/s00497-008-0092-x

  • Delphia, C.M., A.G. Stephenson, C.M. De Moraes, M.C. Mescher. 2009. Inbreeding in horsenettle influences host-plant quality and resistance to herbivory. Ecological Entomology 34(4):513–519.

  • Delphia, C.M., Jason R. Rohr, A.G. Stephenson, C.M. De Moraes, M.C. Mescher. 2009. Effects of genetic variation and inbreeding on volatile production in a field population of horsenettle. International Journal of Plant Science 170:12-20.

  • Good-Avila, S.V., J.I. Mena-Ali and A.G. Stephenson. 2008. Genetic and environmental causes of variation in self-fertility in self-incompatible species. Pp. 33-51. In: V. Franklin-Tong (ed) Self-Incompatibility in Flowering Plants: Evolution, Diversity and Mechanisms. Springer, Heidelberg. 313 pages.

  • Simmons, H.E., E.C. Holmes and A.G. Stephenson. 2008. Rapid evolutionary dynamics of zucchini yellow mosaic virus. J. Gen. Virol. 89:1081-1085.

  • Mena-Ali, L. Keser and A.G. Stephenson. 2008. Inbreeding depression in Solanum carolinense (Solanaceae), a species with a plastic self-incompatibility response. BMC Evolutionary Biology  8:10   doi:10.1186/1471-2148-8-10

  • Du, D., JA Winsor, M. Smith, A. DeNicco and AG Stephenson. 2008. Resistance and tolerance to herbivory changes with inbreeding and ontogeny in a wild gourd (Cucurbitaceae). American Journal of Botany 95:84-92.

  • Good-Avila, S.V., D. Majumder, S. Flemming and A.G. Stephenson. 2008. Characterization of self-incompatibility in Campanula rapunculoides (Campanulaceae) through genetic analyses and microscopy. Botany 86:1-13.

  • Mena-Ali, J. and A.G. Stephenson. 2007. Segregation analyses of partial self-incompatibility in self and cross progeny of Solanum carolinense reveal a leaky S-allele. Genetics 177:501-510.

  • Ferrari, M., J.A. Winsor, D. Du, and A.G. Stephenson. 2007. Inbreeding alters host plant quality and incidence of an insect borne pathogen in Cucurbita pepo ssp. texana. Internat. J. Plant Sciences 168:603-610.

  • Valdivia, E.R., Y. Wu, L-C Li, and D.J. Cosgrove, and A.G. Stephenson. 2007. A Group-1 pollen allergen affects the outcome of pollen competition in Maize. PLoS ONE. 2(1): e154. doi:10.1371/journal.pone.0000154.

  • Ferrari, M.J., C.M. De Moraes, A.G. Stephenson, M.C. Mescher. 2006. Inbreeding effects on blossom volatiles in Cucurbita pepo ssp. texana. Amer. J. Bot. 93:1768-1774.

  • Stephenson, A.G., J.A. Winsor, D. Du, A. DeNicco and M. Smith. 2006. Herbivory by cucumber beetles affects pollen production and pollen performance in a wild gourd. In: Cucurbitaceae 2006. G. Holmes (ed.). North Carolina State University Press, Raleigh, NC. Pp. 301-308.

  • Valdivia, E.R., D.J. Cosgrove, and A.G. Stephenson. 2006. Role of accelerated style senescence in pathogen defense. Amer. J. Bot. 93: 1725-1729.

  • Avila-Sakar, G. and A.G. Stephenson. 2006. Effects of spatial pattern of damage on growth and reproduction in Cucurbita pepo ssp. texana. International Journal of Plant Sciences 167:1021-1028.

  • Hayes, C.N., J.A. Winsor and A.G. Stephenson. 2005. A comparison of male and female responses to inbreeding in Cucurbita pepo ssp. texana (Cucurbitaceae). American Journal Botany 92:107-115
  • Hayes, C.N., J.A. Winsor and A.G. Stephenson. 2005. Multigenerational effects of inbreeding in Cucurbita pepo ssp. texana (Cucurbitaceae). Evolution 59:276-286.
  • Hayes, C.N., J.A. Winsor and A.G. Stephenson. 2004. Environmental variation influences the magnitude of inbreeding depression in Cucurbita pepo ssp. texana (Cucurbitaceae). Journal of Evolutionary Biology 18:147-155.
  • Hayes, C.N., J.A. Winsor and A.G. Stephenson. 2004. Inbreeding influences herbivory in Cucurbita pepo ssp. texana (Cucurbitaceae). Oecologia 140:601-608.
  • Stephenson, A.G., B. Leyshon, S.E. Travers, C. N. Hayes and J.A. Winsor. 2004. Interrelationships among inbreeding, herbivory, and disease on reproduction in a wild gourd. Ecology 85: 3023-3034.
  • Travers, S.E., Mena-Ali, J.A., and A.G. Stephenson. 2004. Phenotypic plasticity in the self-incompatibility system of Solanum carolinense. Plant Species Biology 19: 127-135.
  • Stephenson, A.G., S.E. Travers, J. Mena-Ali, J.A. Winsor . 2003. Pollen performance before and during the autotrophic-heterotrophic growth transition. Phil. Trans. Royal Soc. Lond. B 358:1009-1018.
  • Good-Avila, S.V., T. Nagel, D. Vogler and A. G. Stephenson, 2003. Effects of inbreeding on the male function and self-fertility in the partially self-incompatible herb Campanula rapunculoides (Campanulaceae). American Journal of Botany 90: 1736-1745.
  • Good-Avila, S.V. and A.G. Stephenson. 2003. Parental effects in a partially self-incompatible herb, Campanula rapunculoides L. (Campanulaceae): Influence of variation in the strength of self-incompatibility on seed set and progeny performance. Amer. Nat.
  • Avila-Sakar, G., S. Simmers and A.G. Stephenson. 2003. The interrelationships among leaf damage, anther development, and pollen production in Cucurbita pepo ssp texana (Cucurbitaceae). Internat. J. Plant Sciences 164:395-404.
  • Avila-Sakar, G., L.L. Leist and A.G. Stephenson. 2003. Effects of the spatial pattern of leaf damage on growth and reproduction: Nodes and branches. Journal of Ecology 91:867-879.
  • Good-Avila, S.V. and A.G. Stephenson. 2002. The inheritance of modifiers conferring self-fertility in the partially self-incompatible species, Campanula rapunculoides. Evolution 56:263-272.
  • Poulton, J.L., D. Bryla, R.T. Koide and A.G. Stephenson. 2002. Effects of mycorrhizal infection and soil phosphorus availability on vegetative growth and the female and male functions in two cultivars of Lycopersicon esculentum. New Phytol. 154:255-264
  • Avila-Sakar, G., G.A. Krupnick and A.G. Stephenson. 2001. Resource allocation to growth and reproduction in Cucurbita pepo ssp. texana: Effects of fruit removal. Internat. J. Plant Sci.162:1089-1095.
  • Good-Avila, S.V., F. Frey and A.G. Stephenson. 2001. The effect of partial self-incompatibility on the breeding system of Campanula rapunculoides L. under conditions of natural pollination. Intern. J. Plant Sci.162:1081-1087.
  • Poulton, J.L., R.T. Koide and A.G. Stephenson. 2001. Effects of mycorrhizal infection and soil phosphorus availability on in vitro and in vivo pollen performance in Lycopersicon esculentum. Amer. J. Bot.88:1786-1793.
  • Poulton, J.L., R.T. Koide and A.G. Stephenson. 2001. Effects of mycorrhizal infection, soil phosphorus availability, and fruit production on the male function of two cultivars of Lycopersicon esculentum Mill. Plant Cell & Environment 24:841-849.
  • Stephenson, A.G., C. N .Hayes, M.H.Johannsson AND J.A.Winsor. 2001. The performance of microgametophytes is affected by inbreeding depression and hybrid vigor in the sporophytic generation. Sex. Plant Reprod. 14:77-83.
  • Vogler, D.W. and A.G. Stephenson. 2001. The potential for mixed mating in a self-incompatible plant. Internat. J. Plant Sci.162:801-805.
  • Krupnick, G.A., G. Avila-Sakar, K. Brown and A.G. Stephenson. 2000. Effects of herbivory on internal ethylene levels and sex expression in Cucurbita texana. Functional Ecology 14:215-225.
  • Stephenson, A.G., D.W. Vogler, S.V. Good. 2000. Interrelationships among inbreeding depression, plasticity in the self-incompatibility system, and the mating system of Campanula rapunculoides L (Campanulaceae). Annals of Botany 85: 211-219.
  • Winsor, J.A., S. Peretz and A.G. Stephenson. 2000. Pollen competition in a natural population of Cucurbita foetidissima (Cucurbitaceae). Amer. J. Bot. 87:527-32.
  • Krupnick, G.A., K. Brown and A.G. Stephenson. 1999. The influence of fruit on the regulation of internal ethylene concentrations and sex expression in Cucurbita texana. Internat. J. Plant Sci. 160:321-330.
  • Vogler, D.W., S. Peretz and A.G. Stephenson. 1999. Floral plasticity in an iteroparous plant: The interactive effects of genotype, environment and ontogeny in Campanula rapunculoides (Campanulaceae). Amer. J. Bot. 86:482-492.
  • Dickinson, H.G., J. Doughty, S.A. Hiscock, C.J. Elleman and A.G. Stephenson. 1998. Pollen-stigma interactions in Brassica. In: Control of Plant Development: Genes and Signals. Soc. Exptl. Biol. Seminar Series. Greenland, A., E. Meyerowitz and M. Steer
  • Johannsson, M.H. and A.G. Stephenson. 1998. Effects of temperature stress during microsporogenesis on pollen performance in a wild and cultivated Cucurbita pepo L. (Cucurbitaceae). Internat. J. Plant Sci. 159:616-626.
  • Johannsson, M.H., M.J. Gates and A.G. Stephenson. 1998. Inbreeding depression affects pollen performance in Cucurbita texana. J. Evol. Biol. 11:579-588.
  • Poulton, J.L., D.R. Bryla, R.T. Koide and A.G. Stephenson. 1998. Effects of mycorrhizal infection and soil phosphorus availability on leaf area measurements in tomato. Current Topics in Plant Physiol. 19:314-316.
  • Stephenson, A.G., J.L. Poulton, T-C. Lau and R.T. Koide. 1998. Effects of soil phosphorus level and mycorrhizal infection on the male function of plants. Current Topics Plant Physiol. 19:52-67.
  • Vogler, D.W., C. Das and A.G. Stephenson. 1998. Phenotypic plasticity in the expression of self-incompatibility in Campanula rapunculoides L. Heredity 81:546-555.
  • Delph, L.F, M.H. Johannsson and A.G. Stephenson. 1997. How environmental factors affect pollen performance: ecological and evolutionary perspectives. Ecology 78:1632-1639.
  • Johannsson, M.H. and A.G. Stephenson. 1997. Effects of pollination intensity on the vigor of the sporophytic and gametophytic generation of Curcurbita texana. Sexual Plant Reproduction 10:236-240.
  • Stephenson, A.G., J. Doughty, S.A. Hiscock, C.J. Elleman, S. Dixon and H.G. Dickinson. 1997. The male determinant of self-incompatibility in Brassica oleracea is located in the pollen coating. The Plant Journal. 12:1351-1360.
  • Quesada, M., J.A. Winsor and A.G. Stephenson. 1996. Effects of pollen competition on the reproductive performance of cucurbit hybrids (Cucurbitaceae): F1 and backcross generations. Can. J. Bot. 74:113-118.
  • Quesada, M., J.A. Winsor and A.G. Stephenson. 1996. Effects of pollen selection on progeny vigor in Cucurbita pepo X C. texana hybrid. Theor. Appl. Genet. 92:885-890.

Research Interests:

Cell and Developmental Biology:
Ecology:
Evolutionary Biology:
Genetics:
Physiology and Organismal Biology:
Plant Science: