The 1997 Summer Research Fellows at Davidson are listed below, along with the name and abstract of their research project and the name of their faculty mentors:
Scott
Addison
Dr. Don Kimmel, mentor
Is the volume of the brain proportional to the volume of the body
in orb-weaving spiders?
Abstract: The ratio of brain size to body size in mature females of several species of orb-weaving spider was studied to determine whether behavioral complexity maintains some relationship to the size of an organism¹s brain. These spiders have similar behavior patterns, thus removing that variable from the relationship. Exoskeletons were softened in 6% Na hypochlorite, and serial sections of the cephalothoraxes were prepared. The volumes of the cephalothorax and the brain of each section were determined using computer imaging and analysis. A significant relationship was found between the two in spiders that vary as much as forty-fold in body volume. Smaller spiders allocate more of their body volume to brain tissue than do larger spiders. These results support the argument that behavioral complexity is indeed linked to the ratio of brain size to body size.
Katherine
Okey
Dr. Pat Peroni, mentor
Effects of pollen addition and clonal structure on the maintenance of
andromonoecy in horsenettle (Solanum carolinense).
Abstract: Horsenettle (Solanum carolinense: Solanaceae) is an andromonoecious perennial herb. Andromonoecy is a breeding system in which an individual plant produces both male and hermaphroditic flowers. Steven, Peroni, and Rowell (1995) found evidence of pollen limitation in two Virginia horsenettle populations, and speculated that pollen limitation may serve as a selection pressure that favors male flower production in horsenettle. In order to further investigate the role of pollen limitation in the maintenance of andromonoecy in horsenettle, we designed a field experiment to address the following questions:
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Are fruit and seed production in North Carolina piedmont horsenettle populations pollen limited?
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Do pollen additions affect gender expression?
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What are the means for flower production per plant and gender expression for horsenettle populations from the North Carolina piedmont?
We selected 50 plants in each population and randomly assigned half to a pollen addition treatment and the remainder to a control treatment. Fruit set and percentage of male flowers were greater in the pollen addition treatment than the control for both populations. However, these trends were not significant. We cannot conclude that pollen limitation exists in our North Carolina populations this year. Our power to address this question was limited because only 36% of our plants flowered due to an extended drought and most of the plants produced less than 5 flowers. Longer term investigations will be required to determine if pollen limitation acts to maintain andromonoecy in horsenettle.
Kenneth
Howard
Dr. Pat Peroni, mentor
Genetic relatedness and queen-worker conflict in Leptothorax
ants.
Abstract: We investigated variations in queen number and patterns of reproduction due to varying environmental effects on Leptothorax ant populations at a mountain site near Mountain Lake Biological Station (MLBS) in Virginia and a piedmont site (ERW) near Davidson, North Carolina. The mountain population of L. curvispinosus is facultatively polygynous whereas the piedmont population is a rare case of a strictly monogynous population of this species. The piedmont population produced a more female-biased male allocation ration that the mountain population. At the mountain site, L. curvispinosus coexists with an extensive, facultatively polygynous population of L. longispinosus, a species not found at the piedmont site. Differences in social structure of the L. curvispinosus populations may relate to differences in competitive regimes at the two study sites.
Kelly
Kiefer
Dr. Pat Peroni, mentor
Demography and ecological genetics of buried white campion (Silene
alba) seeds.
Abstract: Many plant species maintain a seed bank. These seed banks may function as reservoirs of genetic variation. Such genetic banks could influence responses to novel selective pressures and ameliorate the effects of inbreeding when population size becomes small. However, inadequate knowledge exists for most species on whether or not differential survival of genotypes in the seed bank actually occurs. Although a seed bank can serve as the genetic "memories" of populations, these "memories" may be selective. White campion, a dioecious perennial herb, has served as the subject of a metapopulation investigation in SW VA for the past decade. Seed dispersal is extremely limited which means that the seed banks could stabilize the dynamics of population fragments by providing means of reestablishing a population and/or by minimizing the effects of inbreeding in a small population. Peroni and Armstrong (in prep) and Peroni, Boozer, Whitehead, Marshall, Kiefer, and Okey (in prep) documented the existence of white campion seed banks, but have little information on the ecological genetics of these pools. We chose to manipulate one environmental factor experienced by buried seeds (darkness), and used maternal families of seeds to address the following questions:
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Do maternal families vary in ability to germinate in the dark?
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How does the relative performance of the maternal families in the dark compare with the performance in the light?
A significant interaction effect (family*treatment) was found for the Whittaker population. Viability differed significantly between the populations, but not among families within the populations. No correlation between mass and percent germination within the populations was found.
Tehnaz
Parakh
Dr. Julio Ramirez, mentor
Unilateral entorhinal cortex lesions induce formation of new electrophysiologically
active neural circuits.
Abstract: As evidenced in the rat model of Alzheimer¹s Disease, sprouting by the surviving neurons following a unilateral entorhinal cortex lesion appears to be a compensatory mechanism for the loss of cholinergic input to the damaged system. Research indicates that the microenvironment following damage is critical to the recovery of the system. Purines present in damaged areas appear to raise levels of endogenous trophic factors and help promote recovery of function. The purine derivative, AIT-082, has been shown to enhance mRNA production of trophic factors, as well as enhance memory-capacity. Therefore, we proposed that administration of AIT-082 following a right unilateral entorhinal cortex lesion (rUECX) would enhance sprouting in the hippocampal circuit. Optical densitometric analysis revealed that the density of cholinergic sprouting in the ventral dentate gyrus in the rUECX-AIT-082 groups was significantly greater than the SHAM/AIT-082 group. No other intergroup differences were observed. Because our small sample size may have contributed to this mild effect, further research using larger sample sizes to increase the power of the analysis is warranted to explore the conequences of AIT-082 administration on sprouting in the hippocampal formation.
Mary
Noel George
Dr. Julio Ramirez, mentor
The role of septodentate sprouting in recovery of memory function.
Abstract: In the present investigation, we examined the effects of an intravenous infusion of basic fibroblast growth factor (bFGF) on the sprouting response observed after unilateral entorhinal cortex lesions in rats. The animals were randomly placed into one of four treatment groups: intact/vehicle infusion, intact/bFGF infusion, entorhinal cortex lesion (ECL)/vehicle infusion, and ECL/bFGF infusion. Animals were sacrificed four days after completion of surgery, the brains were extracted, and the tissue was stained with cresyl violet acetate and Naik acetylcholinesterase (AChE) staining in the outer molecular layer of the dentate gyrus. There was no effect in the molecular layer of the dorsal dentate gyrus; however, there was a significant enhancement of AChE staining in the molecular layer of the ventral dentate gyrus relative to the intact/vehicle infusion group. This increased intensity of staining cannot be attributed to shrinkage of the terminal field or sprouting by the commissural/associational fiber plexus because the width of the outer and inner molecular layers was retained. Therefore, intravenous infusion of bFGF enhances sprouting of the cholinergic septodentate pathway. The administration of bFGF merits future study as a potential clinical tool for the amelioration of neurodegenerative disorders.
Katie
Lannon
Dr. Mark Stanback, mentor
Nest site fidelity in Eastern bluebirds: Costs and benefits of
parasite avoidance.
Abstract: We conducted an experiment to measure indirectly the cost of ectoparasitism associated with within-season nest site reuse. Specifically, we measured the propensity of Eastern bluebirds (Sialia sialis) to switch nest sites between nestings. Birds were initially presented with two clean nest boxes--either a pair of cement boxes or a mixed pair of one cement and one wood box. After the first nesting, nests from half of the occupied boxes were removed. Subsequent nesting choices were then recorded. Because cement boxes are preferred over wood, we measured the bluebirds¹ aversion to nest reuse relative to their aversion to wood boxes. Bluebirds seem to prefer to reuse boxes if they are clean. Bluebirds are willing to switch boxes to avoid reusing a nest, as long as the alternative is a clean cement box. Bluebirds are willing to pay the parasitism costs of nest site reuse in order to avoid an undesirable box type.
Anne
Ford
Dr. Mark Stanback, mentor
Hatching patterns in birds: Testing a critical assumption.
Abstract: Researchers have traditionally defined hatching asynchrony with respect to the difference in size between the largest and smallest chicks in the brood. However, this definition ignores the potential influence of the other chicks in the brood. To test the validity of experiments in which asynchrony is artificially exaggerated, we manipulated Eastern Bluebird (Sialia sialis) broods into two distinct patterns (multiple runt and single runt) with identical total asynchrony. Treatment type did not affect the growth of either "large" or "small" chicks. Although our results tentatively validate assumptions and techniques of previous experiments, larger sample sizes are necessary to provide a critical test.
1997 Summer Research Fellows at Davidson
Hughes Summer Research Fellows '98
