RESEARCH:

My general research interests are in the areas of plant population biology and the ecology and evolution of angiosperm reproduction. The primary focus of my research has been to study the genetic and environmental factors that influence pollen germination and growth, and the ecological and evolutionary implications of variation in pollen growth rates. I have explored the effect of variation in the strength of pollen competition on offspring vigor in Dianthus chinensis (Caryophyllaceae) and two distylous species, Turnera ulmifolia (Turneraceae) and Anchusa officinalis (Boraginaceae). These studies indicate that increased pollen competition results in higher offspring fitness as measured by characteristics such as seed size, seedling weight, seedling competitive ability and time to flowering.

In other studies I have addressed the effect of various environmental factors on pollen germination and growth. I have carried out long term studies on the effects of simulated acid rain on alpine flora in the Snowy Mountains of Wyoming. The aim of this research was to examine pollen sensitivity to low pH and to investigate the potential effects of acid rain on reproductive and vegetative processes in alpine plants. All species showed a decrease in pollen germination at low pH, and most species had a significant decline in pollen germination below pH 4.5. A long-term study on the effect of simulated acid rain on reproductive and vegetative processes in Aquilegia caerulea (Ranunculaceae) indicates that this species is particularly sensitive to acid rain stress. Similar studies examining the effect of simulated acid rain are underway in forest understory plants of the Fernow Experimental Forest in West Virginia.

Additional research thrusts include a study of ecotypic variation in plants growing on serpentine soils, the role of essential oils in protecting plants (and their neighbors!) from fungal infection, and the use of pollen selection techniques to identify suitable plant species for phytoremediation efforts. I am currently directing an NSF-funded project entitled: Growing Our Own: Supporting the Next Generation of Plant Science Research At Howard University. This initiative will improve facilities for plant science research in the Biology department, support graduate and undergraduate research in plant science, and facilitate pre-college mentoring and outreach efforts.

SELECTED PUBLICATIONS:

McKenna, M.A., N.V. Summers and M. Bond. 1994. Effects of pH on pollen germination, reproduction and growth in alpine plants. In: Stephenson, A.G. and T.H. Kao (eds.), Pollen-Pistil Interactions and Pollen Tube Growth. American Society of Plant Physiologists, Rockville, MD.

McKenna, M.A. 1992. Pollen competition and heterostyly. pp. 225-246 in S. Barrett (ed) Evolution and Function of Heterostyly, Monographs in Theoretical and Applied Genetics. Springer-Verlag, Zurich.

Thomson, J.D., M.A. McKenna, and M. Cruzan. 1989. Temporal patterns of nectar and pollen production in Aralia hispida: Implications for reproductive success. Ecology 70:1061-1068.

McKenna, M.A. and J.D. Thomson. 1988. A technique for sampling and measuring sugar content of small amounts of floral nectar. Ecology 69: 1306-1307.