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Graduate Students
[Dr. Hormiga's Lab] My main research interests are in phylogeny, evolution and biogeography of spiders: relationships between ecologically linked taxa, divergence time estimation using molecular sequence data and phenomenon related to changes in rates of evolution in different spider groups. Working with my advisor, Professor Gustavo Hormiga, I am investigating the systematic, evolution and biogeography of the goblin spider genus Lionneta (Oonopidae), endemic to Madagascar and the Seychelles Islands. Those two islands were both part of the Gondwanaland, which started to break apart about 167 million years ago. Because Madagascar and the continental Seychelles broke off from the Gondwanaland super continent more than 160 million years ago, they constitute a living example of species evolution in isolation. I am also interested in the relationships between the genera within the Oonopid group, to which Lionneta belongs.
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[Dr. Brown's Lab] I am interested in the effects of nanoparticles on mammalian embryonic development. Nanoparticles are incredibly small chemical structures being produced for use in extremely miniaturized electrical circuits, in medicine and as tools for cell and molecular biologists. As a result of their small size and high surface area-to-volume ratio, nanoparticles possess unique physical and chemical properties that are distinct from the properties of larger particles of the same material, and therefore may produce unexpected biological responses. My research, working with Dr. Ken Brown, involves examining whether nanoparticles injected into pregnant rodents have the ability to cross the placenta and reach the developing embryos, and whether these nanoparticles adversely affect embryonic and fetal development.
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[Dr. Hormiga's Lab] My journey into the arachnid world started 10 years ago in Colombia, my home country. For my undergraduate research project, I spent 10 months climbing trees in the Amazon rainforest to investigate which spiders live in the canopy of the rainforests trees and what kind of microhabitats they are using. After my graduation, I worked in the spider collection of the Instituto de Ciencias Naturales in Colombia. One year later, in 2005 I came to USA to work on the systematics of a family of Neotropical Opiliones at Harvard University, and then as a laboratory technician in the American Museum of Natural History in the National Science Foundation-sponsored project "Assembling the tree of life: Phylogeny of Spiders." Finally in the fall 2007, I started my doctoral studies in Systematics and Evolution at GW, under the supervision of Professor Gustavo Hormiga. My main Ph.D. research focuses on the phylogeny and biogeography of Mimetidae, a cosmopolitan family of spiders known as "cannibal" spiders because of their araenophagic habits. I will be using molecular, morphological and behavioral data to study their phylogenetic relationships and classification.
http://www.gwu.edu/~spiders/people.htm
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[Dr. Clark's Lab] My research interests revolve around the systematics and evolution of Anolis lizards. Currently, I am working with Dr. James Clark (GWU) and Dr. Kevin de Queiroz (National Museum of Natural History, Smithsonian Institution), reconstructing the phylogeny of a subgroup of poorly known South American Anolis, the Dactyloa clade, using morphological (external and osteological) and molecular characters (mitochondrial ND2 and COI, and nuclear RAG-1 genes). My project has given me the perfect excuse to go to Colombia, Ecuador and Venezuela to collect tissue samples for my molecular analyses and visit herpetological collections. I am also studying the association between some morphological characters correlated with habitat use (fore-, hindlimb, tail and body length, and number of digital lamellae), and the evolution of these associations in Dactyloa species.
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[Dr. Brown's Lab] Born and raised in Kingston, Jamaica, I earned a B.S. in Biology at Washington College, on the eastern shore of Maryland. I then worked in a prenatal cytogenetics lab at Johns Hopkins University for two years, where my interest in developmental biology grew. This led me to the lab of Dr. Ken Brown, studying early embryogenesis, specifically, the role of serotonin on early sea urchin embryogenesis. It has been shown that 5-HT is present in invertebrate and vertebrate embryos that have not yet developed a nervous system. It is our aim to understand the role that pre-nervous 5-HT through interactions of ligands for specific 5-HT receptors, looking at the developmental regulation of tryptophan hydroxylase activity, as well as the signal transduction mechanisms involved. These studies suggest that 5-HT acts as a regulator of embryo cleavage, cell movements and cell differentiation. These studies will give us insight into processes common to all embryonic development.
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[Dr. Clark's Lab] Like most other young males of our species, I always wanted to be a dinosaur when I grew up. Sadly, that major wasn't available at any of the colleges I was accepted to. While I was working on my B.S. in Geology at UMASS Amherst, I took a course in vertebrate evolution and decided that the next best thing to being a dinosaur would be doing research on dinosaurs. This led me to work with Professor James M. Clark. During the summers of 2005 and 2006, I accompanied Dr. Clark on his excavations of Middle to Late Jurassic deposits in Xinjiang, China. The outcrops were beautiful, the fossils plentiful, our hosts were hospitable and the food was delicious (if you are into mutton). I hope to continue collaborating with Chinese researchers in the future. I am interested in the systematics of coelurosaurian theropods, a group of carnivorous dinosaurs that includes birds. I am currently working on describing various theropod skeletal remains from Dr. Clark's field project in Wucaiwan.
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Julie Ghosh, jghosh@gwu.edu [Dr. Smith's Lab]
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[Dr. Church's Lab] After graduating with a B.S. in Biology from Salisbury University, I came to George Washington to work with Dr. Sheri Church to learn more about polyploidy and hybridization in the plants.. My dissertation research focuses on understanding polyploidy influence on species barriers and whether it facilitates or prevents interspecific hybridization in the plant genus Houstonia (commonly known as the bluets). These little bluets (although more pink and purple in color!) offer an excellent opportunity to study hybrids and polyploids (which make up 30-70% of flowering plants). I am also interested in using my research to help protect endangered members of the genus by using molecular methods to determine levels of genetic diversity within and among populations of the federally-listed Houstonia montana and the state-listed Houstonia longifolia. While I enjoy working at the bench with my pipettes, having the chance to hike and rock climb on collection trips has really expanded my hoirizons when it comes to field work! I hope to ultimately combine ecological studies and molecular methods to study plant speciation. My overall interests include evolutionary biology, molecular evolution, conservation biology and ecological genetics.
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Paaqua Grant, paaqua@gwu.edu
[Dr. Johnson's Lab] What do ballet and genetics have in common? Not much, but I love them both. I studied ballet since I was 6 years old, and danced professionally for four years after I graduated high school and before coming to college. I finally decided to pursue my other passion: science. I earned my B.S. in Biology here at GW, including many hours in the lab of my undergraduate, and now graduate, advisor Professor Diana Johnson. I am investigating a variety of topics, including identifying and characterizing the genes responsible for various eye-color mutations in Drosophila melanogaster; looking into the gene regulatory networks of forkhead, aka FOX genes in Xenopus laevis; and looking for novel maternal transcription factors in early stage X. laevis embryos. I have just completed my first year as a graduate student, and look forward to more teaching and studying and learning in the years ahead.
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Alexandra Herrera Martinez, alexhm@gwu.edu
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[Dr. Burns's Lab] I spend a good deal of my time pondering the evolutionary history of a group of freshwater South American fishes. This group is the family Characidae, which includes the "tetras" that are sold in many aquarium shops. An integral part of my investigation is phylogenetic inference for a subset of characids, the "Clade A" characids. Evidence for the phylogeny will come in the form of genetic sequences, ultrastructural aspects of spermatozoa, histology, other soft anatomy, and osteology. Many of the species in this group are inseminating. That is, sperm are somehow transferred from males to their mates. However, fertilization (i.e., joining of an egg and sperm) might take place outside of the female as she extrudes her eggs. Correlated with insemination could be the complex mating behaviors observed in characid fishes, the evolution of curious structures that may secrete pheromones from the gills and caudal fins, sperm cells with derived shapes, and other structures that are found in only one of the two sexes. Which came first, the chicken or the egg? Did insemination evolve before the suite of traits mentioned above or did those traits "allow" insemination to arise? How many times did insemination evolve? How did the geological history of South America affect the evolution of these fishes? My research may answer some of these questions (except the one about [delicious] poultry). My co-advisors are Drs. John Burns and Stan Weitzman (National Museum of Natural History, Smithsonian Institution). I received my B.A. from Boston University and my M.S. from the College of Charleston.
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[Dr. Burns's Lab] My research focuses on the taxonomy and systematics of Rasbora, a remarkably diverse genus in the family Cyprinidae, which is the most species-rich family of freshwater fishes. This genus is distributed throughout a vast geographical area encompassing the Indian subcontinent, Southern China, Indochina, Sundaland, and even occurring on eastern side of Wallace's Line (Mindanao and the Lesser Sunda Islands). In Sundaland, Rasbora inhabits almost all types of freshwater habitat and predominantly occupies the river basins throughout the region. However, being poorly studied, this genus has been long recognized as a "catch-all" group, and thus is still taxonomically problematic primarily due to no single diagnostic synapomorphy recognized to delimit the genus. My dissertation will have emphasis on Sundaland's Rasbora. The goal of my research is to resolve the taxonomic problems in the form of new species description, generic revision, and phylogenetic reconstruction. The data set of characters for phylogenetic inference will be acquired through an array of multifaceted approaches, which will include DNA sequencing technique, scanning electron microscope (SEM) analysis, soft tissues histology, and osteological study. The resulting phylogeny, together with the data of species distribution, will be used to infer an area cladogram of Sundaland. Ultimately, in comparison with area cladograms of other taxa, the historical biogeography of Sundaland will be inferred. I have conducted regional estuarine and freshwater ichthyofauna inventories in two poorly explored areas of Indonesia, which are Northwestern Sumatra (2006) and Southeastern Kalimantan (2007). I am co-advised by Dr. John Burns (GW) and Dr. Lynne Parenti (Division of Fishes, Smithsonian Institution). I received my B.Sc. in Biology from Universitas Indonesia (Indonesia) before coming to GWU.
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Bonnie Lun, bonster@gmail.com, [Dr. Smith's Lab]
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Audrey Majeske, majeskea@gwu.edu
[Dr. Smith's Lab] I am interested in the evolution and processes of immune systems. The purple sea urchin, Strongylocentrotus purpuatus, is the closest relative to the chordates and possesses an innate immune system, which up until now has been thought to contain generally conserved receptors and effector molecules that respond to broad classes of pathogens. However, a growing set of recent evidence suggests that in invertebrates and plants, innate immune systems are able to diversify through previously unknown mechanisms to generate novel, pathogen-specific immune responses. My work focuses on the 185/333 protein family that produces a diverse family of transcripts and proteins in response to infection. Working with Dr. Courtney Smith, my primary aims are to characterize the localization of proteins in the animals and define the function(s) of genes in this family, to better understand how and why the extraordinary level of diversity is generated.
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Karine Posbic, keposbic@gwu.edu
[Dr. Church's Lab] I graduated with a B.S. from Mount Saint Mary’s University, where I found my passion for biology. I came to GWU in the Fall of 2008 to work with Dr. Sheri Church. Here, I study population genetics of the marbled salamander (Ambystoma opacum). Specifically, I use molecular techniques to quantify genetic variation within and among populations (within a larger metapopulation found in VA) of this salamander species in order to measure population subdivision and ultimately dispersal between the populations. My goal is then to combine my genetic data with previous mark-recapture field data in order to obtain a more accurate measure of migration occurring within the larger metapopulation. My research enables me to do both lab and field work and integrates my interests in population genetics, molecular evolution, and ecology. It also incorporates my interest in conservation biology since salamanders, like most amphibian species, are currently facing serious population declines.
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Karen Poole, kepoole@gwmail.gwu.edu, [Dr. Forster's Lab]
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[Dr. Brown's Lab] My research focuses on the role of serotonin in preneuronal development. Serotonin is a neurotransmitter with a variety of roles from regulating behavior to involvement in irritable bowel syndrome. Prior to neuronal development serotonin is present in varying concentrations throughout specific stages of early development. I am investigating the types of serotonin receptors present at different stages of early development, specifically gastrulation. Once I determine the receptors present, I will clarify the signal transduction pathways they affect. As a result, I will then determine the receptors responsible for developmental processes such as cell migration, adhesion, proliferation and death. I work with Lytechinus pictus, a sea urchin to study the effects of serotonin. I intend to relate this work to cooption and duplication events in evolution. I came to GW with a B.S. in biology from Loyola University of New Orleans. I currently work at GW as the Supervisor of Biological Laboratories and received my masters in Forensic Science from GW. I work with Dr. Ken Brown and Kamali Carroll attacking this investigation of serotonin and its affect on early development from many angles.
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Elisha Sigmon, hesigmon@gwu.edu [Dr. Lill's Lab]
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[Dr. Hernandez's Lab] Have you ever wondered why your pet goldfish makes that funny face? Goldfish (Carassius auratus), like many fish, exhibit the ability to protrude their premaxillae, a trait that has evolved at least twice within fishes and has led to massive radiations of the groups that possess this means of feeding. I study premaxillary protrusion in zebrafish (Danio rerio), a member of the Cyprinidae family to which the goldfish belongs. The zebrafish has become a model organism but the laboratory techniques that have been developed for studying genetics and biomedical questions with this fish can also be exploited to study many evolutionary and even functional questions. The zebrafish and other members of the Cyprinidae family effect premaxillary protrusion using a bone called the kinethmoid which is a synapomorphy for their entire order, Cypriniformes. The kinethmoid bone is tucked behind the premaxillae, is entirely suspended by ligaments, and flips on its end when the upper jaw is protruded. What is the purpose of this bone? How does it develop? Is it possible that the kinethmoid is a sesamoid bone, like our patella? In what ways is this mode of premaxillary protrusion different than other modes? In answering these questions, I hope to arrive at a story that is intriguing to both evolutionary and biomedical scientists alike. I come to GW with a B.S. in Biology from Mount St. Mary's College in Emmitsburg, Md., and a few years of cell therapy production experience. I work with Dr. Patricia Hernandez.
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[Dr. Lill's Lab] I am interested in community ecology and tropical entomology, especially interspecific interactions such as parasitism and mutualism. I came to GW in Fall 2007 to work with Dr. John Lill on parasitoid-caterpillar-hostplant interactions in the New World tropics. Parasitoids (usually flies or wasps) are distinguished from parasites in that parasitoids kill their host, whereas parasites do not. The unique life history of both lepidopteran caterpillars and their parasitoids makes this an excellent system in which to investigate questions related to trophic interactions and enemy-free space. This summer I am excited to begin field research on limacodid caterpillars with Dr. Lill. Next year, I hope to attend the Organization for Tropical Studies (OTS) graduate course in Costa Rica to help me develop ideas on a specific tropical study system.
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Saurabh Trikha, trikha@gwu.edu [Dr. Jeremic's Lab]
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[Dr. Johnson's Lab] As I teenager I was amazed to see my normally docile 12lb terrier guard the family home with the ferocity of a grey wolf. As a young adult I have been amused watching my cat stalk chipmunks in the backyard, the way that a lion may stalk a gazelle. It is clear that within the DNA of our tame animal companions lies the history of the world's most successful group of predators, the Carnivores. The published whole genome sequences of the domestic dog and domestic cat allow scientists to use comparative genomics to study the evolution of the entire Carnivore order. With the guidance of Dr. Marc Allard, and Dr. Jill Pecon-Slattery (National Cancer Institute), I am studying the evolution Carnivores with emphasis on the Felidae family using short interspersed nuclear elements (SINEs). Before returning to GW for my doctorate I worked in the biotechnology sector, received an M.S. in Forensic Science in 2002 from GW and a B.S. in Biology in Physiology and Neurobiology in 2000.
Laboratory of Genomic Diversity at the National Cancer Institute: http://home.ncifcrf.gov/ccr/lgd/overview/index.asp
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Stuart Willis, scwillis(at)gwu.edu
[Dr. Orti's Lab] I am interested in species, particularly in their diagnosis, origin and evolution. My research has focused on freshwater fishes from South America, primarily the Amazon, which exhibits the largest assemblage of freshwater fishes on Earth.
Species discrimination is a fundamental goal of systematics, and molecular data provide a tool for understanding the ways in which individual and population genetic history affect how species boundaries arise and are maintained through time (i.e. reproductive isolation). My work on a group of important food and sport fishes from South America, the peacock basses (actually cichlids of the genus Cichla), has the goal of determining an effective way of combining what are typically considered population genetic (e.g. microsatellite) and phylogenetic (e.g. DNA sequences) data sources to understand the species boundaries, phylogeny, and circumstances and influence of hybridization in these fishes.
The collection of molecular data from Neotropical fishes also provides the opportunity to understand the historical biogeography of this region. The Amazonas River Basin dominates the landscape of modern South America, but the river in its current configuration is at most 8 million years old. Before that time, it is believed that a number of changes occurred which altered the drainage of an even larger river which flowed northward along the (much smaller) Andes Mountains to empty ultimately into the Caribbean Sea north of Venezuela. These changes, coupled with the inference from fossil data that many or most contemporary South American fish genera had emerged by the Oligocene or early Miocene, suggests that changes in river drainage patterns have probably had major influences on speciation and hybridization through time (via vicariance, geodispersal, range expansion, and secondary contact). Although historical biogeography is still a relatively narrative science, my research attempts to use combinations of population genetic and phylogenetic data, and molecular phylogenies from multiple groups, to understand how geological changes affected species living in those regions. Personal Website
M.Sc. Zoology, University of Manitoba (2006), B.Sc. Wildlife & Fisheries, Texas A&M University (2003)
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