Professor
Adjunct, School of Public and Environmental Affairs

Ph.D., Duke University, 1982
Postdoctoral Fellow, University of Texas, 1982-83

Program Affiliation: Evolution, Ecology and Behavior | Microbiology | Plant Biology

Research Groups Affiliation: Ecology | Evolution | Microbiology | Plant Biology

Phone: 812/855-8158
Fax: 812/855-6705
Email Keith

Clay Lab Website

IU Teaching & Research Preserve

Center for Research in Environmental Sciences

We are interested in how microbial interactions affect dynamics of ecological communities. Recent research has revealed unsuspected microbial diversity and evidence for its central role in many ecological processes. Ongoing research falls into four areas.

Microbial Community Ecology of Tick-Borne Human Pathogens -- In collaboration with Clay Fuqua, Curt Lively, Mike Wade (all at Indiana University) and Bob Pinger (Ball State University), we are investigating the microbial community ecology of tick-borne human pathogens. We are characterizing the microbial communities of three local tick species to analyze patterns of co-occurrence among microbial taxa. In particular, we are interested in whether avirulent symbionts may exclude human pathogens from tick communities. Ticks carry a diversity of microbes acquired by feeding on infected hosts or by vertical transmission through eggs, and are the number one source of vector-borne disease in the US. In Indiana, the black-legged tick (Ixodes scapularis, vector of Lyme Disease) is invading from the north while the lone star tick (Amblyomma americanum, vector of human ehrlichiosis) is invading from the south. The dog tick (Dermacentor variablis, vector of Rocky Mountain Spotted Fever) is widely established throughout the state. This situation provides an opportunity to evaluate how changing tick distributions and overlapping host ranges, and microbial interactions within ticks, affect the prevalence of tick-borne human pathogens. Initial results have revealed a novel group of vertically-transmitted bacteria (Arsenophonus) in all tick species this examined (Grindle et al. 2003). Microbial interactions within arthropod vectors represent a potential determinant of human disease.

Soil-borne Pathogens and Forest Dynamics -- We are examining the role of soil-borne pathogens in forest communities. This work is in collaboration with recent post-doctoral associate Alissa Packer (now at Susquehanna University) and current post-doc Kurt Reinhart. Positive or negative feedbacks may occur where soil microbiota either favor the survival and growth of a particular species or actively inhibit it (Reynolds et al. 2003). Black cherry (Prunus serotina) is attacked by soil- borne pathogens (Pythium species) that inhibit seedling establishment in the vicinity of adult trees, in accordance with the Janzen- Connell hypothesis, and reduce growth of survivors (Packer and Clay 2000, 2003a). We are examining how negative feedback changes with successional age of the community, assessing the host specificity of Pythium species causing damping- off in black cherry, and evaluating whether other temperate tree species are similarly affected by soil- borne pathogens. Recent results have demonstrated that negative feedback between black cherry and its soil community develops very rapidly (in a few weeks) in its native range (Packer and Clay 2003b), but is apparently absent in Europe where black cherry has become highly invasive (Reinhart et al. 2003, see also Clay 2003). Other student projects in the lab are investigating the ecology of invasive plants and the role of microbial interactions during invasions. Our results provide valuable comparative data with tropical forests, and have practical applications for forest and orchard management, and for ecological restoration.

Endophyte Symbiosis and Biodiversity -- Many grasses are infected by systemic fungal endophytes that occur intercellularly within leaves and seeds of their hosts (Clay and Schardl 2002). Past work has shown that endophyte infection often enhances host growth, reduces pest damage, and increases resistance to abiotic stresses (Fortier et al. 2000, Matthews and Clay 2001). Closely related endophyte species span a continuum ranging from mutualist to pathogen where mutualistic endophytes are asymptomatic and seed-transmitted (Kover and Clay 1998). A current graduate student is investigating the basis of this variation in a single endophyte-grass interaction and a recent graduate student (Jean Pan) documented how infection alters clonal growth patterns of its host (Pan and Clay 2002, 2003). In collaboration with post-doctoral researcher Jennifer Rudgers, we are investigating the consequences of the rapid spread of endophyte-infected tall fescue grass (Festuca arundinacea) in natural and managed communities for grassland diversity and productivity (Clay and Holah 1999). Long-term field experiments have been established to investigate how endophyte infection affects the ability of tall fescue to persist in plant communities and how enhanced herbivore resistance (to the prairie vole, Microtus ochrogaster) affects plant-plant interactions (Fortier et al. 2000, Rudgers et al. 2003). This research is revealing how a microbial symbiont can alter community and ecosystem-level processes.

Periodical Cicadas and Forest Community Dynamics -- In collaboration with James Speer at Indiana State University, we are analyzing the effects of recent (2002 - Brood XXIII) and upcoming (2004 - Brood X) emergences of 13- and 17-year periodical cicadas on forest succession. Brood X is likely to be the largest insect outbreak on Earth. Much is known about cicada biogeography, systematics, behavior, and predator satiation but relatively little research has investigated their impacts on host trees and forest dynamics, and how these effects depend on landscape patterns. Cicada emergences may result in strong selective pressures among species with long-term consequences for forest succession. We are contrasting forest community composition in high density vs. cicada-free sites. In addition, we experimentally manipulated colonization in selected sites by netting blocks of early successional forest during the emergence period to reduce oviposition and subsequent root colonization. Periodical cicadas may serve as a useful model for other, less predicable biotic disturbances.

In addition, a variety of research projects by graduate and undergraduate students are ongoing. They include the relationship between mixed mating systems in jewelweed and rust infection in native populations, correlates of vertical and horizontal endophyte transmission in Elymus hystrix, a native woodland grass, and the invasibility of forest communities by exotic shrubs as a function of successional age and distance to roadways.  Most of these projects have both field and greenhouse components.

D. Civitello, S. L. Flory and K. Clay. 2008. Exotic grass invasion reduces tick-borne disease risk. Journal of Medical Entomology 45: 867-872.

K. Clay, O. Klyachko, N. Grindle, D. Civitello, D. Oleske and C. Fuqua. 2008. Microbial community ecology of ticks: prokaryotic diversity, distribution and interactions in the lone star tick, Amblyomma americanum. Molecular Ecology 17: 4371-4381.

Rudgers, J. and K. Clay. 2008. An invasive plant-fungal mutualism reduces arthropod diversity. Ecology Letters 11: 831-840.

Tintjer, T., A. Leuchtmann and K. Clay. 2008. Variation in horizontal and vertical transmission of the endophyte Epichloë elymi infecting the grass Elymus hystrix. New Phytologist 179:236-246.

Clay, K., Reinhart, K., Rudgers, J., Tintjer, T., Koslow, J. and S. L. Flory. 2008. Red queen communities. Pp. 145-178, In Ecology of Infectious Diseases: Interactions between diseases and ecosystems. (V. Eviner, F. Keesing and R. Ostfeld, Eds.). Princeton University Press, Princeton.

Koslow, J. M. and K. Clay. 2007. The mixed mating system of Impatiens capensis and infection by a foliar rust pathogen: Resistance, local adaptation, and fitness consequences. Evolution 61: 2643-2654.

Klyachko, O. B. Stein, N. Grindle, K. Clay and C. Fuqua. 2007. Localization and visualization of a Coxiella-type symbiont within the Lone Star Tick Amblyomma americanum. Applied and Environmental Microbiology 73: 6584-6594.

Rudgers, J. A., Holah, J., Orr, S. P. and K. Clay. 2007. Forest succession suppressed by an introduced plant-fungal symbiosis. Ecology 88: 18-25.

Finkes, L. K., Rudgers, J. A., Cady, A. B., Clay, K. and J. C. Mulroy. 2006. A fungal mutualist affects the composition of spiders in an old field. Ecology Letters 9: 347-356.

Clay, K., Holah, J. and J. A. Rudgers. 2005. Herbivores cause a rapid increase in hereditary symbiosis and alter plant community composition. Proceedings of the National Academy of Science USA 102:12465-12470.