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Nason Lab Members
This page provides brief overviews of the research of current and past members of the Nason Lab.
Greetings from San Buto, Baja California Sur, Mexico!
From left to right: Rodney Dyer, Wendy Marussich, Ryan Rapp, Kevin Day, Dan Gates, and John Nason.
Graduate Students
Kevin Day
Masters student in Interdepartmental Ecology and Evolution (EEB)
Kevin is interested in the ecological and evolution of figs and fig wasps. Of particular interest to Kevin are mechanisms of diversification and coexistence within the community of non-pollinating fig wasps that exploit the fig-fig wasp mutualism. His research focuses on the four species of Idarnes wasps that co-occur on the Sonoran Desert rock fig, often in the same fig! These wasps differ in several morphological characters, most notably ovipositor length, permiting Kevin to test pre-existing hypotheses as to how differences in ovipositor length may facilitate coexistence. Kevin's work builds on the discoveries of past Nason Lab student Kristy Bernhard (see below).
A. Brad Duthie
Ph.D. student in in Interdepartmental Ecology and Evolution (EEB)
Brad is currently working on the application of graph theory for the purpose of resolving species interactions in ecological communities. His primary foci at this time include: resolving species interactions in the fig/fig-wasp mutualism surrounding Ficus petiolaris, analyzing different edge selection procedures for graphical models, and examining the spatio-temporal dynamics of species interactions. A current manuscript of his in preparation includes the use of a recently developed edge selection procedure to resolve species interactions in eight fig wasp species, which complete their life-cycle on F. petiolaris. Players in this system include a pollinating wasp, several exploiters of the mutualism, and a parasitoid of an exploiter.
You can link to Brad's web page here
Dan Gates
Masters student in Interdepartmental Ecology and Evolution (EEB)
Dan's research investigates mutualism stability in the Sonoran Desert rock fig, Ficus petiolaris. Among New World figs, F. petiolaris is unique both for being the most northern ranging and for occurring in the most extreme desert environments. Previous conservation-oriented research on the fig-fig wasp mutualism indicates that, in general, a fig population must have >100 trees to buffer its species-specific pollinator from local extinction. In contrast, many populations of F. petiolaris are so small and spatially isolated that it is unclear how viable pollinator populations, and hence fig reproduction, is maintained. Dan is testing test the hypothesis that (1) more asynchronous flowering within F. petiolaris trees, (2) increased duration of the receptive flowering phase, and (3) increased clonal spread, benefit both individual plant fitness and fig wasp survival. As fig populations are noted for year-round fruit production providing food resources critical to many vertebrate frugivores, the conservation implications of this research extend beyond the study species to issues of community and ecosystem diversity.
You can link to Dan's web page here
Adam Kuester
Ph.D. student in Interdepartmental Genetics (IG)
Adam's primary interests lie in understanding how insect herbivores interact with their plant hosts, both from an ecological as well as a molecular-biochemical perspective. His current research interests focus on interactions between a wild Sonoran desert cotton species, Gossypium davidsonii, and its associated insect herbivores.
You can link to Adam's web page here
Hui Yu
Post-doctoral researcher
Hui comes to us from the South China Botanical Garden where she has worked on the dioecious fig Ficus hirta and its associated pollinating and non-pollinating fig wasps. There is growing evidence of exceptional fig wasp mediated pollen dispersal in monoecious figs, many of which are large canopy trees (see Nason et al. 1996, 1998). In contrast, ecological and regional-scale genetic studies suggest that in small, understory, dioecious figs, such as F. hirta, pollen dispersal should be much more restricted. We tested this prediction by using nuclear microsatellite (nSSR) and chloroplast sequence (cpDNA) data to infer the ratio of pollen to seed mediated gene migration (r) in F. hirta. Despite predictions we found evidence we found unusually low nuclear differentiation (FST = 0.059) and high chloroplast differentiation (FST = 0.729) among 15 sample populations separated by up to 2850 km. Taking into account differences in inheritance (biparental vs maternal) and ploidy (diploid vs haploid), the equilibrium estimate r = 21.4 was far greater than expected for a species with restricted pollen dispersal. These results, and their implications for breeding population sizes in F. hirta and the maintenance viable fig wasp populations, are summarized in a manuscript in review for Molecular Ecology. In a second paper (in prep.) we are using these genetic data to examine the phgylogeography of F. hirta, and the influences of pollen and seed movement on geographical patterns of genetic variation. Finally, also while at ISU Hui has extended her research on fig and fig wasp interactions to New World taxa, combining ecological and microsatellite data to investigate geographical variation in the breeding structure of the fig wasp pollinator (Pegoscapus sp.) of the Sonoran Desert rock fig, Ficus petiolaris.
You can link to Hui's web page here
Past members of the Nason Lab
Postdoctoral Associates
Dr. Rodney Dyer
Assistant Professor, Department of Biology, Virginia Commonweath University
As a prostoc in the Nason lab, Rodney worked on two primary projects. One involved developing graph theoretic methods for the analysis of population genetic data. In Dyer & Nason (2004) we showed how intraspecific population genetic struction can be quantified using the mathematics of graph theory. Investigating the utility of graph-theoretic approaches is an ongoing research direction. The second focus of Rodney's research in the lab investigated the affects of post-Pleistocene range expansion in Sonoran Desert plants.
Rodney and I continue to collaborate to understand the symmetry/asymmetry of gene flow in coevolving plant-insect mutualisms and host-parasite relationships and in May 2006 began an NSF supported Collaborative Research project focused on this problem. Recent papers in collaboration with Rodney's postdoc Ryan Garrick are a product of this interaction (Garrick et al. 2008, Garrick et al. 2009a, Garrick et al. 2009b). An education outreach component of our NSF supported project, Rodney and I teamed to teach two International Study Abroad courses, in Spring 2007 and 2008, that engaged undergraduates from both Iowa State University and Virginia Commonweath University in team oriented field research in the Sonoran Desert of Baja California, Mexico. These courses were co-instructed with Dr. Mary Harris (ISU) and Dr. Anne Wright (VCU).
Dr. John Stireman
Assistant Professor, Department of Biology, Wright State University
John's postdoctoral research in my lab investigated the ecological and evolutionary forces that promote genetic divergence and speciation in insects. In particular, he pioneered a community-level approach that tests the pervasiveness of host race formation as a mechanism of diversification in phytophagous insects and their insect parasitoids. As a model system he focused on the sister species of goldenrods, Solidago altissima and S. gigantea, and the phylogenetically diverse assemblage of insects attacking both hosts (representing a number of different feeding guilds). In a paper in Evolution (Stireman et al. 2005) we show host race formation to be common in goldenrod herbivores (4 of 10 species). Further, in a paper in Proceedings of the Royal Society (Stireman et al. 2006) we show that host race formation may often cascade from herbivores to their parasitoids (2 of 3 species). These results have important implications for our understanding of the origins of insect biodiversity and, because all of these host races are morphologically and taxonomically cryptic, levels of diversity even in well studied insect communities.
Broader overview of our research on host race formation in goldenrod insects
Dr. Mi Yoon Chung
Assistant Professor, Department of Biology, Gyeongsang National University, Korea
Mi Yoon's research centers on the conservation genetics of terrestrial orchids, plants that are of conservation concern worldwide. Her postdoctoral work in the Nason lab focused on two projects. In one we investigated processes influencing the evolution of demographic and genetic structure in Cymbidium ghoeringii at different spatial scales and how this structure has been influenced by the illegal harvesting of plants by orchid enthusiasts. A paper describing this research was published in Ecological Applications (Chung and Nason 2007). In the second project we developed and then tested stage-specific predictions as to how fine-scale demographic and genetic structure changes during the course of a population’s successional history. As model organism we investigated Hemerocallis thunbergii (Liliaceae), a nocturnal flowering and hawkmoth-pollinated herbaceous perennial with rapid population turnover dynamics. A paper describing this research was published in Molecular Ecology (Chung et al. 2007). These are but two of several papers published between 2002 and 2007 in collaboration with Mi Yoon and colleague Dr. Myong Gi Chung, also at Gyeongsang National University. (See Publications)
Graduate Students
Kristy Bernhard
Masters Degree in Interdepartmental Ecology and Evolution
Currently living in Lusk, Wyoming, with daughter Frannie and husband Tony (Tony is an engineer for Union Pacific Railroad)
Kristy's research tested the hypothesis that very specialized and intimate mutualistic or parasitic interactions between organisms lead to cospeciation and, at deeper taxonomic levels, congruent phylogenies. As a study system she focussed on the Sonoran rock fig, Ficus petiolaris, and its non-pollinating floral parasite, the wasp Idarnes sp. Surprisingly, Kristy found that the Idarnes on F. petiolaris consists of four genetically and morphologically distinct lineages. A broader phylogenetic perspective obtained using sequence data from a diversity of Idarnes species (in collaboration with Dr. Carlos Machado, U. of Arizona) indicates that the co-occurrence of these lineages on a single host reflects a history of host switching events. Comparative analyses reveal important phylogeographic and ecological differences between lineages. A paper presenting these results is currently in revision for Molecular Ecology.
Young Jin Chun
Ph.D student in Interdepartmental Ecology and Evolution
Co-advised with Kirk Moloney in EEOB
Young
Jin is interested in the ecological and genetic mechanisms underlying
the success of invasive plants. His research focuses on differences in
phenotypic plasticity, adaptation, and genetic diversity between
invasive N. American and non-invasive European populations of purple
loosestrife (Lythrum salicaria) in terms of phenotypic
plasticity and genetic diversity. A paper describing invasive vs.
non-invasive differences in multivariate phenotypic plasticity was published in Ecology (Chun et al. 2007) while our work describing genetic consequences of colonization and invasive range expansion was published in Molecular Ecology (Chun et al. 2009).
Jennifer DeWoody
Masters Degree in Botany
Currently Biologist and Lab Manager for the National Forest Service's Genetic Electrophoresis Laboratory (NFGEL)
in Placerville, California
Jennifer’s research, conducted in collaboration with Dr. Marian Smith at Southern Illinois University, used population genetic techniques to quantify the dispersal dynamics of Boltonia decurrens, a member of the Asteraceae currently on the Federal List of Threatened Species. This early successional species, endemic to the floodplain of the Illinois River, exhibits strong metapopulation dynamics with frequent population extinction and colonization. Jennifer’s Masters work consisted of two projects relevant to the management and conservation of this threatened species. In one she quantified dispersal and mixing processes underlying population founding and how they structure genetic variation at the population and inter-population levels. The results of this research were published in Conservation Genetics (DeWoody et al. (2004). In the other project, Jennifer tested for hybridization between B. decurrens and a widespread congener, B. asteroides, revealing molecular evidence of interspecific recombination restricted to the two sites where they are known to occur in sympatry. We are currently preparing this latter work for publication. In addition to the above two papers, since Jennifer's graduating from ISU we co-authored a review paper on mitigating microsatellite scoring errors that was puiblished in Molecular Ecology Notes (DeWoody et al. 2006).
Kalyan Dudala
Masters Degree in Interdepartmental Genetics
Currently in a PhD Program in the Department of Genetics and Development at Columbia University
Kalyan's research involved the development and application of graph theoretic methods for the analysis of gene expression data. This work was being conducted in collaboration with Dr. Steve Wittham (Plant Pathology) who provided a well characterized Arabidopsis gene expression data set for model development.
Vicente Faria
Ph.D student in Interdepartmental Ecology and Evolution
Co-advised with Gavin Naylor, Florida State University
Working
primarily with Gavin, Vicente's interests are in molecular systematics
and biogeography with special focus on sawfishes. His research focused on
morphological and molecular reconstructions of phylogenetic
relationships among extant sawfishes, as well as molecular assessments
of the geographical structure of their populations.
Lucia Gutierrez
Ph.D student in Plant Breeding and the Interdepartmental Program in Ecology and Evolution
Co-advised with Jean-Luc Jannink in Agronomy (now at Cornell University)
Lucia utilized quantitative genetic and molecular genetic approaches to
investigate the impacts of domestication on the phenotype and genetic
architecture of barley. Her approach was a comparative one, examining
wild progenitors of barley as well as domesticated lines. A paper in Crop Science (Gutierrez et al. 2009) examines targets of selection in domesticated barley, while a paper we are completing for Molecular Ecology develops and applies methods of analyzing population pairwise QST versus FST data to investigate the nature of selection on quantitative traits in wild barley. During the course of her Ph.D., Lucia also completed a minor in Statistics with Phil Dixon (ISU Statistics).
Kristy Halverson
Masters Degree in Interdepartmental Ecology and Evolution
Currently in PhD Program in Science Education at the University of Missouri, Columbia
Kristy's research investigated intraspecific variation in polyploidy in flowering plants and its impacts on host use in associated insect herbivores. Using flow cytometry to determine plody level, she found that populations of the goldenrod, Solidago altissima, consist of mixtures of 2N, 4N, and 6N plants and that host use by different insect species is highly non-random. Some species are strongly associated with 2N plants while others with 4N or 6N plants, a pattern that persists across different local populations. Our findings concerning geographical variation in polyploidy were published in American Journal of Botany (Halverson et al. 2008a), while the effects of ploidy level on insect host use are described in a paper in Oecologia (Halverson et al. 2008b).
Broader overview of our research on host race formation in goldenrod insects
Fall 09 classes begin Monday, August 24
