Research Interests:
Fundamental questions that pique
my interest are how and why certain organisms occur where they
do. To that end, I am passionate about quantifying and
understanding these patterns. In particular, I am fascinated
by fungal and fungal-like plant pathogens because they offer
the opportunity to quantitatively examine spatio-temporal
patterns within a uniform host stand. My feeling is that many
biological patterns go undetected either because research is
not conducted at the appropriate spatio-temporal scale or
because a seemingly uniform pathogen population may actually
have structure and dynamical properties at the genetic level.
As such, my work is at the interface of quantitative
epidemiology and population genetics.
My research interests can be broadly categorized into the following areas:
· Population ecology
· Plant pathology
· Epidemiology
· Quantitative ecology
· Community ecology
· Mycology << check out
my fungal photos
· Protistology
Brown Rot Fine-Scale Epidemiology:
My current research, under the direction of Harald
Scherm,
is on the
fine-scale spatial epidemiology and population biology of Monilinia spp., which is
an important pathogen of stone fruits, such as cherry and
peach. There are three projects that I'm working on:
3-Dimensional
Spatial Patterns within Tree Canopies
Using cherry as a model system, I worked with Dr. Imre Holb
at the University of Debrecen in Hungary to create
3-dimensional maps of various symptom types (caused by M. laxa) within
organically managed cherry trees. At the University of
Georgia, I have collaborated with Ashley Askew (Ph.D.
candidate, advised by Dr. Lynne Seymour), to develop a
statistical analysis program in Matlab that is able to analyze
the aggregation and association of symptom types within the
complex and irregular 3-dimensional tree canopy. Work is
currently underway to analyze the spatio-temporal patterns of
disease during an entire epidemic of M. fructicola in peach.
Fine-scale
Population Structure and Dynamics
Simply understanding spatial patterns within a tree canopy is
helpful in validating the importance of inoculum sources,
however, it does not tell us about reproductive strategies or
tell us whether spatially aggregated infections were caused by
strains of the same or different origin. To accomplish that, I
have worked with the guidance of Dr. Travis Glenn to develop a
robust set of polymorphic microsatellite genetic markers de novo via
double-enrichment. These markers will be used to develop a
unique genetic profile for all fungal isolates obtained in
individual trees during an entire season. This analysis
will provide insight into the genetic structure (is the
population clonal or are all totally unrelated?) and
3-dimensional spatial dynamics within a tree canopy.
This research is especially important with respect to making
management recommendations to limit development of fungicide
resistance, which is a significant problem in Georgia.
Multinucleosis and
the Parasexual Cycle in M.
fructicola
Monilinia fructicola is
known to be multinucleate, however, the genetic identity
(whether same or different) of the nuclei has not been
determined, which may serve as an important source of genetic
diversity. In this project, I aim to quantitatively assess the
number of nuclei per conidium using flow cytometry and also
create transformed lines of GFP-labeled nuclei in order to
determine if heterokaryosis will occur in vitro. This information may lead
to a better understanding of the sources of high levels
genetic diversity in a fungus that rarely presents the sexual
stage.
Tree Canopy Biodiversity Research:
My master's was completed at the University of Central Missouri in 2007 under the direction of Harold Keller. In this research, I examined the communities and distribution of myxomycetes (true slime molds) present on trees and grapevines in Great Smoky Mountains National Park. In my research, I found that although a tree with a neighboring grapevine may be spatially close, bark characteristics (most important being pH) was a greater determinant in the species occurrence and richness of myxomycetes than any other factor. Furthermore, the biodiversity of other epiphytes (lichens, myxobacteria, ascomycetes) were also not a determinant for myxomycetes. This research has led me to the opinion that the major determinant of myxomycete species living on bark is subtle difference in the microflora (bacteria and other protists) that serve as the nutritional source for myxomycetes. I speculate that myxomycete species have specialized nutrition to different epiphytic bacteria that are more sensitive to bark pH than the myxomycetes themselves. However, these ideas have yet to be validated.
This research gained national attention for use of the tree
climbing technique and was twice featured on National
Geographic. Even after graduating from UCM, I have
continued to publish on myxomycetes and enjoy teaching
students about myxomycetes.
Peer-Reviewed Publications:
Everhart, S.E., A.
Askew, L. Seymour, I.J. Holb, and H. Scherm. 2011.
Characterization of three-dimensional spatial aggregation and
association patterns of brown rot symptoms within intensively
mapped sour cherry trees. Annals
of Botany doi: 10.1093/aob/mcr029 [pdf]
Everhart, S.E. 2010. Upper canopy collection and identification of grapevines (Vitis) from the tree canopy of select forests in the southeastern United States. Castanea 75:141–149. [pdf]
Keller, H.W., and S.E. Everhart. 2010. Importance of myxomycetes in biological research. Fungi 3(1):13–27. [pdf]
Everhart, S.E., J.S. Ely, and H.W. Keller. 2009. Association of tree canopy myxomycetes with epiphytes and bark characteristics. Botany. 87:509–517. [pdf]
Keller, H.W., S.E. Everhart, M. Skrabal, and C.M. Kilgore. 2008. Tree Canopy Biodiversity in Temperate Forests: Exploring islands in the sky. Southeastern Biology 56:52–74. [pdf]
Keller, H.W. and S.E. Everhart. 2008. Myxomycete species concepts, monotypic genera, the fossil record, and additional examples for good taxonomic practice. Revista Mexicana de Micologia 27:9–19. [pdf]
Everhart, S.E. and H.W. Keller. 2008. Influence of bark pH on the occurrence and distribution of tree canopy myxomycete species. Mycologia 100:191–204. [pdf]
Everhart, S.E. and H.W. Keller. 2008. Life history strategies of corticolous myxomycetes: The life cycle, fruiting bodies, plasmodial types, and taxonomic orders. Fungal Diversity 29:1–16. [pdf]
Keller, H.W., C.M. Kilgore, S.E. Everhart,G.J. Carmack, C.D. Crabtree, and A.R. Scarborough. 2008. Myxomycete plasmodia and fruiting bodies: unusual occurrences and user friendly study techniques. Fungi 1:24–37. [pdf]
Kilgore, C.M., H.W. Keller, S.E. Everhart, A.R. Scarborough, K.L. Snell, M.S. Skrabal, C. Pottorff, and J.S. Ely. 2008. Tree canopy research and student experiences using the double rope climbing method. Journal of Botanical Research Institute of Texas 2:1309–1336. [pdf]