Department of Biology Student Research Projects
Lee Wheless '05 was part of a team studying retinal ganglion cell branching and growth cone extension.
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5/9/2005
Contact: Bill Giduz 704/894-2244 or bigiduz@davidson.edu
DNA microarrays: A guide to teaching chips
Allison Amore ‘05, Sheena Bossie ’05, Associate Professor of Biology A. Malcolm Campbell, Max Citrin ‘05, Erin Cobain ’05, Megan McDonald ‘05, Marieta Solé ‘05, Emily Wilson ’05.
DNA microarrays are becoming increasingly prevalent because this technology provides investigators the opportunity to explore simultaneously the interactions among all genes in an organism’s genome. Our group effectively designed a microarray and printed teaching chips for a genomics laboratory course. Teaching chips provide students with a thorough understanding of microarray methodology but do not necessitate the use of expensive RNA samples or genomic DNA. Rather than traditional RNA hybridization, the probes we used are oligonucleotides that are detected with Genisphere's 3DNA kit. This method is advantageous because students have the opportunity to learn through the active creation and analysis of microarrays while the cost of reagents is minimized. This poster describes our experimental methods and discusses the merits of incorporating similar investigative experiments into undergraduate curriculum. We explored many of the intricate steps necessary to produce good results and met course goals as we practiced communicating complex procedures through oral and written formats. We also optimized a printing protocol to make similar experiments more accessible for future students. Integrating comprehensive genomic research opportunities into undergraduate education will facilitate advancement of the field of genomics, thus broadening the potential medical applications of microarray technology.
The effects of seed age on seed viability, seedling performance, and sex ratios in white campion (Silene latfolia)
Sarah Budischak ’05, Associate Professor of Biology Patricia Peroni, Jonathan Ripperton (UNC-Asheville)
In order for seed banks to be an effective evolutionary strategy, seeds must not only remain viable, but also be able to germinate, grow, and compete against conspecifics and other competitors after years of burial. Using white campion (Silene latifolia), a dioecious perennial that maintains a dormant seed bank, as a model species, we examined how age affects the viability and germination rate of seeds and the performance of seedlings. Seeds were collected annually from four southwestern Virginia populations over a 5-10 yr period and then stored under dry, laboratory conditions. Some seeds remained viable after 11 years, but percent viability varied among populations. Increasing seed age was associated with significant decreases and delays in germination. Second, we planted germinated seeds in the greenhouse to assess seedling performance. Seedlings that originated from younger seeds emerged and produced true leaves significantly earlier than seedlings from older seeds. Seedlings from older seeds also tended to have significantly smaller leaves and higher survival rates than those from younger seeds. Sex ratios of seedlings did not deviate significantly from 50:50. The decreased and delayed initial growth of seedlings from older seeds may put them at a competitive disadvantage to those from younger seeds.
Sarah Budischak '05 talked with Chris Paradise, assistant professor of biology, about her research on the effect of urbanization on box turtles.
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The natural history of box turtles (Terrapene carolina) in an urbanized landscape
Sarah Budischak ’05, Associate Professor of Biology Michael Dorcas, Joy Hester ’05, Stephen Price ’03.
Globally, many turtle species are experiencing population declines due to anthropogenic causes. Eastern box turtles (Terrapene carolina) are important components of the biota of eastern forests and in developing areas. In 1999 we initiated a long-term mark-recapture study of eastern box turtles in the vicinity of Davidson College, Davidson, NC. We used data from this study to describe the natural history characteristics of this box turtle population and to examine potential effects of urbanization. Specifically, we examined meristic characteristics, turtle condition, activity patterns, population structure, and growth rates in conjunction with the amount of anthropogenically modified habitat near each turtle’s collection location. Males and females exhibited different, seasonal patterns of activity and body condition, measured using the residual of a mass/carapace length ratio. Growth rates decreased with age and varied between developed and forested habitats. Proportionally, the oldest turtles were found in areas with the most extensive forest cover. Condition did not vary by amount of forest cover for males or females. Natural history studies, like this one, which describe basic characteristics and how those characteristics are affected by urbanization, form the first critical step in developing sound conservation strategies for box turtles in the eastern US.
The effects of Toxorhynchites rutilus on natural treeholes
Charlie Chrisawn ’07, Ben Kittinger ’05, Assistant Professor of Biology Chris Paradise
Natural treeholes, small aquatic habitats, are useful for studying top down control in communities. The top predator in treeholes, Toxorhynchites rutilus, is a ferocious mosquito that is only a predator in the larval state. Our study focuses on seven full censuses that spanned ten months and investigated twenty-eight different natural treeholes in three different locations in Davidson, North Carolina. Our objective was to find the effects of T. rutilus on the treehole community. After examining the data, we can conclude that T. rutilus, widely assumed to be generalist predator, has differential effects on species in the community. Toxorhynchites rutilus had no effect on scirtid beetle density (Helodes pulchella) while it has large negative effects on density of the midge Culicoides guttipennis. Effects on mosquitoes and species richness were equivocal, but the predator may have some seasonal negative effects on mosquito density and positive effects on richness. Generalizations about the effects of predators in treeholes and top-down control in communities will be discussed.
Zebrafish embryos are most severely affected by earlier and longer exposures to sub-lethal concentrations of malathion
Sarah Davis ’05, Assistant Professor of Biology Barbara Lom
Pesticides contaminating water can have teratogenic effects on non-target organisms, such as amphibian and fish embryos. Malathion, used to reduce mosquitoes, is an organophosphorus pesticide that inhibits acetylcholinesterase (AChE). Previous studies have shown that zebrafish exposed to malathion have fewer hepatic cells, abnormal ovaries, skeletal deformities, decreased lengths, reduced eyes, and pericardial edemas. This study 1) examined if zebrafish had sensitive periods to malathion during the first 96 hours of development and 2) visualized AChE activity in pesticide-treated embryos. Recently fertilized zebrafish embryos were exposed to a sub-lethal malathion concentration for various 24- or 48-hour windows, or for the entire 96-hour period following fertilization. Embryos were morphologically analyzed at 96 hours and stained to evaluate AChE activity. Exposure to sub-lethal doses of malathion for 96 hours had the most significant effects on zebrafish development, altering abdominal morphology and stunting overall growth, while malathion exposure during the first 48 hours had similar significant, though less drastic developmental consequences, and 24-hour exposure did not visibly alter zebrafish embryogenesis. These results correlated with the extent of AChE inhibition observed by various staining techniques. Thus zebrafish embryos do experience windows of development in which they are differentially sensitive to malathion’s teratogenic effects.
Ben Kegan ’05 and Leslie Smith ’06 worked with Assistant Professor Chris Paradise on the biology of treeholes -- water filled cavaties that support a wide variety of life.
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Malathion decreases heart rate and alters cardiac morphology in embryonic zebrafish (Danio rerio)
James Barnes, Sarah Davis ’05, Jennifer Hoekstra ’05, Assistant Professor of Biology Barbara Lom
Malathion, an organophosphorous pesticide commonly used to control mosquitoes, can inadvertently affect non-target species in aquatic systems. Zebrafish are a model organism for developmental toxicology. These fresh water fish produce large numbers of offspring that are sensitive to environmental changes. The transparency of the zebrafish embryo allows for the careful study of cardiac form and function. We investigated malathion’s effects upon heart rate in zebrafish by rearing embryos in individual wells for the 72 hours following fertilization in three treatments: tank water, 0.03% acetone (vehicle control), and 2.5 mg/L malathion. At 72 hours, heart beats were counted for 15-second intervals using light microscopy. Kruskal Wallis non-parametric statistical analysis revealed that malathion-treated fish had significantly lower heart rates than both controls (p<0.0001). To determine if malathion affects cardiac morphology, we reared embryos for 24, 36, 48, and 72 hours in malathion or control solutions. We immunostained embryos with a myosin antibody (MF20) and used confocal microscopy to visualize cardiac morphology. Preliminary observations suggest that malathion-treated hearts do not have the characteristic bending pattern of control hearts, nor do they have proper chamber formation. Thus it is likely that the pesticide malathion adversely affects cardiac form and function in embryonic zebrafish
Ethylmethanesulfonate (EMS) mutagenesis screen for a new allele of the no mitochondrial derivative (nmd) gene in the fruit fly Drosophila melanogaster
Amanda Aldridge, McArthur Assistant Professor of Biology Karen Hales, Lindsay Nakaishi ’04
We conducted an EMS screen on Drosophila fruit flies to generate a new allele of the no mitochondrial derivative (nmd) gene that is associated with sterility in male flies. Characterizing different alleles of the nmd gene will to help to better understand the mitochondria function during spermatogenesis. nmd mutant flies have mitochondria that do not align properly during meiosis and instead are dispersed around the meiotic spindle, which results in abnormal mitochondria function during the spermatogenesis and ultimately sterility. We exposed 250 yw;?/Cyo males to 9.0 µL (0.35 % solution) of EMS for 18 hours. EMS exposure was followed by two crosses to create independent mutant strains from the mutagenized founder males. We tested 682 individual male lines and discovered one male line that tested positive for sterility. A complementation test was conducted on the possible new mutation fly line in order to determine the mutations are in nmd. The testes of males with the possible new mutation were dissected and examined under the microscope to detect the failure of mitochondrial aggregation and abnormal mitochondria in the cells of the testes.
Novel organic compounds DRR 3 and DRR 5 affect growth rate differentially in model bacteria Escherichia coli, Salmonella typhimurium, and Staphylococcus simulans
Associate Professor of Biology Karen Bernd, Kimberly Newton, Andrew Pickens
The synthesis of new compounds is vital in the search for better and more effective drugs. Purine-derived and purine-analog drugs are at the forefront of these new synthesizing processes. Using our existing library of purine-analogs, we tested compound 1-DRR-5 (DRR-5) and 1-DRR-3 (DRR-3) and its starting materials for biological activity in three microbial species: Escherichia coli (E.coli), Salmonella typhimurium (Salmonella), and Staphylococcus simulans (Staphylococcus). Using these three species, we were able to look at how structure (chemical properties) and function (biological properties) are related. Results show that DRR-5 has the capability to increase in the growth rate of E.coli while DRR-3 decreased the growth rate of all three bacterial species. These results show that these novel organic compounds can have either a trophic or toxic effect on bacterial growth depending on the side chain or amount of branching.
HIV/AIDS and popular culture: A new web-based educational tool
Anna Harger ‘02, Emily Wilson ‘05, Associate Professor of Biology David Wessner
To address the need for improved HIV/AIDS education, we developed a website to disseminate information about HIV/AIDS through art, music, television and film (www.bio.davidson.edu/projects/aidspopculture). Additionally, information about the major scientific advancements for each period is provided. We investigated the effectiveness of this multi-media website as a teaching tool for HIV/AIDS education by assessing its impact on a group of 103 first year college students. An anonymous questionnaire addressing HIV/AIDS knowledge and awareness was given to each participant. Some participants saw the site prior to answering the questionnaire; other participants simply answered the questionnaire. We calculated the fraction of correct answers for each objective question and compared the results of the two groups using a Mann-Whitney U statistical test. We found that the group who was exposed to the website prior to answering the questionnaire answered a significantly higher fraction of questions correctly as compared to those students who did not receive the website (p<0.0001). With this multi-media website that examines popular culture references to HIV/AIDS, then, we have developed an effective HIV/AIDS educational tool. Ideally, this site will be useful both in academic environments and as an information source for the general public.
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