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Research
Abstracts |
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Reconstructing
a Permian Tropical Forest:
Vegetational Compositions and Patterns of Herbivory |
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Jorge
Alvarez William DiMichele,
Ph.D. Conrad Labandeira,
Ph.D. |
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In recent
years the interest for the study of plant-insect interactions has risen
in the scientific community. However, very little has been published on
this about Early Permian floras. The late Paleozoic was a time of very
drastic changes for Earth's climate, shifting from an Icehouse to a Greenhouse
climate. This is the most recent model for such an event that is available
for study. To have a better idea of what the ecosystem was like during
such an event, we chose samples from four locations of the Colwell Creek
Pond site of north-central Texas, which corresponds to this time period,
and made qualitative and quantitative analysis of the flora. The site
is composed by series of rock layers, called redbeds that occur throughout
north-central Texas. During the Permian, this was the western tropical
margin of the Supercontinent Pangea and the specimens found here are classic
examples of an Early Permian biota. By analyzing and quantifying the insect
interactions with this flora and comparing it to various other projects
currently taking place in the United States, Brazil, and South Africa,
it might be possible to establish a pattern for the herbivory of these
insects. There were three dominant species in the flora of these four
sites: Auritifolia waggoneri (common - 34.14% ), Walchian conifer
type 1 (common - 34. 14%), Taeniopteris type 1(common - 25. 33
%). The majority of the specimens were rare, with only 1 or 2 counts in
some cases. Out of all the specimens Auritifolia waggoneri showed
the most damage, with 58.71% of the samples being affected. The other
two affected were Taeniopteris type 1 (minimum damage) and conifers
type 1 and 3 (with what appear to be galls). Very few other taxa were
affected, but their count was so low that a significant count could not
be achieved. This research was supported by a grant from the Latino Initiatives Fund. |
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Ontogenetic
Changes in Shell Microstructure of Freshwater Gastropods from
Lake Tanganyika (Cerithioidea, Paludomidae) |
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Emily
Armgardt Ellen Strong, Ph.D. |
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Ancient
lakes and their unique faunas present unparalleled opportunities for studying
the patterns and processes of evolution and speciation. Lake Tanganyika,
an ancient lake located in the Western Rift Valley of southeast Africa
is known for hosting many endemic species including fishes, crabs, and
gastropods. Unlike many other freshwater gastropods, the gastropods of
Lake Tanganyika have highly decorated and thickened shells. West &
Cohen (1996) have identified predator/prey co-evolution between gastropods
and shell crushing crabs as the source for the unusual shells found in
the lake. They quantified the number of cross-lamellar layers, up to four,
in a sub-sample of species, and postulated that the additional shell layers
impede predation by shell crushing. However, this study did not closely
examine the ontogenetic sequence of the shell microstructure present in
the shell. Eighteen different species were embedded in resin and examined
with scanning electron microscopy to reveal the ontogenetic sequence of
microstructure. The emergent pattern in the shell microstructure of many
different species was a very simple larval shell, with additional variant
cross-lamellar layers added during the juvenile stage, and then simplification
of the layers when adult. This finding runs contrary to a predator/prey
hypothesis because the additional layers claim to inhibit predation are
not present in the adult. This research was supported by grants and donations to the Research Training Program. |
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Body
size evolution in deep-sea ostracodes
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Julia
Brown Gene Hunt, Ph.D. |
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This study examined evolutionary trends in the body size of deep-sea ostracodes, and aimed to elucidate the mechanisms underlying Cope’s Rule: the tendency for body size to increase over time. Previous work has indicated that increases in body size of the ostracode genus Poseidonamicus were significantly correlated with decreases in deep-sea temperatures during the Cenozoic. Sixteen ostracode lineages from two sites on the Indian Ocean floor were examined to see if the same pattern appeared across additional sites and species. Ostracode body size (approximated by log-area) was measured using the software Image J and charted over a period of approximately 40 million years. The number of body size increases and decreases were counted between adjacent samples, and entire sequences were tested for directional trends using random walk models. Although ostracode body size showed intervals of both increase and decrease over time, there is evidence of an overall trend toward larger size, as body size increased over time in thirteen of sixteen lineages. Including both sites and all lineages, there were 38 body size increases between adjacent time periods, and 28 decreases, and the number of significant increases (13) nearly doubled the number of significant decreases (7). Concordant increases in body size emerge during the late Oligocene at DSDP site 253 and during the Pliocene at DSDP site 254. However, the exact patterns of body size evolution appear to differ between species and sites. This indicates that although a cooling global climate may be driving the general trend toward increasing body size in deep-sea ostracodes, there are many other local and species-specific factors capable of influencing body size evolution. This research was supported by grants and donations to the Research Training Program. |
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F-OH-
Substitution and Thermal Effects on the Crystal Structure of Pegmatitic
Topaz
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Madison
Barkley Mike Wise, Ph.D. |
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Pegmatites are intrusive igneous rocks that are characterized by unusually large grain sizes (> 20mm). There are two geochemical types of granitic pegmatites, LCT and NYF. LCT pegmatites are rich in lithium (Li), cesium (Cs), and tantalum (Ta) and are usually associated with orogenic granites. NYF pegmatites are related to anorogenic granites and are enriched in niobium (Nb), yttrium (Y), and fluorine (F). Topaz is a fluorine-rich mineral that commonly occurs in pegmatites; however, topaz is more common in NYF pegmatites than in LCT pegmatites. The focus of this project was to examine the changes in topaz crystal structure caused by F-OH- substitution and to investigate the structural changes due to temperature in order to determine if there are structural differences between topaz from LCT pegmatites and topaz from NYF pegmatites. In this study, 32 topaz samples from 26 localities were analyzed for unit-cell parameters, fluorine content, trace element content, and heating effects. Cell parameters were calculated from X-ray diffraction data, and fluorine content was obtained by electron microprobe analysis. As consistent with other topaz studies (Alberico et al. 2003), the b unit-cell dimension decreases with increasing F content. Also consistent was a less defined decreasing trend in the a unit-cell dimension as F content increases. No correlation was found between the c cell dimension and any other cell-dimension or compositional variation. Plots of the pegmatitic topaz from this study show distinct and separate linear trends between NYF and LCT pegmatites when comparing the b unit-cell dimension to the F content. Trace element analysis by X-ray fluorescence shows the presence of Ge, Cr, Pb, Ga, W, and Rb but yields no correlation between trace elements and unit-cell variations. Selected samples were chosen for a heat study. Samples were heated at 700oC for 1 hour. After heating, the unit-cell volume of the topaz generally decreased but no trends separating NYF pegmatites from LCT pegmatites were found. This research was supported by grants and donations to the Research Training Program. |
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The
Origins of Layered Carbonates in Peridotite Xenoliths
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Bryan
Cockrell Ed Vicenzi, Ph.D. |
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Layered
carbonates are found in lava-coated peridotite mantle xenoliths from the
Sverrefjell basaltic volcano, which erupted through a glacier one million
years ago during the Pleistocene and is located in the Bockfjord volcanic
complex in Svalbard, Norway. Some carbonate globules are nearly identical
to ones detected in Martian meteorite ALH84001 in size, shape, and chemical
zoning and thus, the Sverrefjell depositions serve as a terrestrial analog
of Martian aqueous alteration in ultramafic rocks. This investigation,
based predominantly on two peridotite xenoliths, sought to characterize
the variety of the carbonates' (and associated low-temperature silicates')
textures and mineral chemistry in order to constrain their source fluid(s)
and relative timing. The depositions, referred to as globules, were found
as infilling at mineral grain boundaries and grain junctions. X-ray spectra,
extracted from an energy dispersive detector mounted on a variable pressure
scanning electron microscope (VPSEM), aided in the initial mineralogical
characterization of the phases in globules from the two samples. Wavelength
dispersive x-ray spectroscopy performed with an electron probe microanalyzer
(EPMA) confirmed the fine-scale (submicrometer) intergrowth of silicates
with carbonates in one sample and the presence of pure carbonates in the
other. Several carbonates rich in Ca, Mg, and Fe were commonly observed
while the most frequently observed silicate was an Fe-rich clay (saponite).
Textures are consistent with carbonate deposition by hydrothermal waters
as previously proposed. Multiple populations of carbonates and later silicate
veins clearly indicate complex secondary mineralization by low-temperature
fluids. Magmatically driven hydrothermal waters are likely responsible
for dissolution of many of the veinlets as well as precipitation of the
carbonates while ambient glacial groundwater may be the source for deposition
of late saponitic clays. This research was supported by grants and donations to the Research Training Program. |
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Hydrovolcanics
on Mars: Comparison of Home Plate and Zuni Salt Lake, New Mexico
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Megan
Ennis Tim McCoy, Ph.D. |
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The Mars
Exploration Rover mission objective is to find evidence of past water.
While Opportunity’s landing site showed clear evidence in the water-lain
sediments of the bedrock, Spirit has operated for more than two years
before finding promising evidence for water. After traversing the Columbia
Hills, Spirit approached the light-toned circular feature (~80m in diameter)
known as “Home Plate”. In this work, we have tested whether
Home Plate was formed by a hydrovolcanic eruption as a single event, or
by eruption and subsequent aeolian reworking, by comparing the Mars deposits
with various hydrovolcanic sites in New Mexico. To accomplish this goal,
observations were made during one week of field work (June 11-June 16,
2006) completed in New Mexico at sites analogous to Home Plate. The goal
of the field work was to document deposits of terrestrial hydrovolcanic
maar volcanoes. Sites visited include Valles Caldera, White Rock Canyon,
Montoso Maar, and most importantly Zuni Salt Lake. At Zuni Salt Lake a
stratigraphic section, at a comparable scale to that of Home Plate (~2m),
was measured and described. Samples were collected at these various sites
for further analysis and later reference. Photographic images were taken
along with descriptive field notes in order to document the features that
were observed. These images were then compared to the images of Home Plate.
We noted similarities, including low angle cross-bedding, accretionary
lapilli, bomb sags, tephra beds, fine-grained finely layered units, alternating
layers of coarse and fine clasts or tephra and vesicular basalt lag deposit
cap. Differences, including collapse features, accidental (bedrock) material,
and palagonite were also noted as being present at Zuni Salt Lake while
absent at Home Plate. While each of the New Mexico sites demonstrates
similar features to those seen at Home Plate, Zuni Salt Lake provides
the most accurate terrestrial analog based on lateral extent and overall
scale. Zuni Salt Lake is classified as a maar on the basis that slumping
around the crater rim is evident and a large amount of accidental (bedrock)
material is present. Lack of slumping and accidental material indicates
that Home Plate is probably not a maar, but a tuff ring dominated by magma
material. Low angle cross beds are found in both types of deposits; therefore,
features found at Home Plate can result from a base surge produced by
a hydrovolcanic eruption. The hydrovolcanic tuff ring model allows for
all features observed at Home Plate, including the cross-bedding, to be
accounted for within a single volcanic event, without requiring a later
stage of wind-reworking. This style of eruption indicates that there once
was water at or below the surface of Mars. This research was supported by grants and donations to the Research Training Program. |
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Morphological
and genetic variation in Amazonian antwrens
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Katherine
Faust Terry Chesser, Ph.D. |
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One important
objective of systematic biology is to classify variation in the natural
world into a meaningful evolutionary and taxonomic framework. In the field
of ornithology, this has most often been done using qualitative analysis
of plumage characters. These assessments, however, may not reflect natural
evolutionary units (species or subspecies). Now, with new genetic and
morphological techniques available, it is possible to quantitatively assess
variation among and within species and determine whether current taxonomic
designations do, in fact, reflect evolutionary history. This project evaluated
genetic and morphological variation among subspecies of three Amazonian
antwrens in the genus Myrmotherula: M. longipennis, (Long-winged
Antwren) M. menetriesii, (Gray Antwren) and the species complex
M. hauxwelli/guttata (Plain-throated/Rufous-bellied Antwrens).
This is the first quantitative study of plumage variation and is among
the first comprehensive studies of genetic variation in pan-Amazonian
birds. All subspecies that were sequenced formed distinct genetic units,
and female plumage variation was found to be distinctive within nearly
all of these units. Only M. h. hauxwelli was difficult to distinguish
on the basis of quantitative morphological characters. Furthermore, the
subspecies M. hauxwelli clarior appears to contain two distinct
genetic groups, and although no comparative genetic information was available,
two distinct plumage groups were also identified within M. menetriesii
berlepschi. These results emphasize the importance of independent
quantitative examination of plumage in combination with genetic analyses.
The concurrence between morphological and genetic data in these birds
also mirrors findings from other emerging studies of tropical birds, whereas
studies of temperate zone birds have often found plumage differences to
be more pronounced than genetic differences. This research was supported by grants and donations to the Research Training Program. |
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The
White Plague: Skeletal Evidence of Tuberculosis
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Paige
Hamilton Dave Hunt, Ph.D. |
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Literature
searches on the prevalence of tuberculosis lesions in 20th Century skeletal
remains have revealed a disparity in expression of lesions on the ribs.
This study intended to investigate the incidence of skeletal evidence
of tuberculosis to clarify inconsistencies in the reported literature.
A sample of 150 individuals was randomly-selected from three cause of
death subgroups: pulmonary tuberculosis, non-specific tuberculosis, and
non-tuberculosis. Results from this study show that a significant number
of individuals with pulmonary tuberculosis (66%) and with non-specific
TB (62%) displayed rib lesions, while only 16% of those dying from non-tuberculosis
demonstrated this lesion type. Spinal lesion were also evaluated in this
study. The frequency of both rib and spine lesions in individuals dying
from pulmonary TB and non-specific TB was 38% and 36%, respectively, while
only 8% of non-tuberculosis displayed both lesions. Although other possible
diseases may respond in a similar way, the presence of lesions on the
visceral side of the ribs and in conjunction with lesions on the anterior
body of the spine would be highly diagnostic for an individual suffering
from tuberculosis. This research was supported by grants and donations to the Research Training Program. |
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Pipestone
Provenance: Sourcing Prehistoric Pipestone Artifacts Within Museum Collections
Using Reflectance Spectroscopy
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Jayme
Job Eric Hollinger, Ph.D. |
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Sourcing
archaeological artifacts has proven extremely useful in discerning prehistoric
trading patterns and cultural contacts. This study widens the scale of
many past sourcing projects by considering an entire museum’s pipestone
collections rather than an individual object type or site. Advancements
in the technology of geophysical sourcing, such as non-destructive reflectance
spectroscopy, have made access to many previously restricted artifacts
possible. By analyzing much of the pipestone collection housed by the
Smithsonian’s National Museum of Natural History and National Museum
of the American Indian using reflectance spectroscopy, existing notions
of prehistoric trade on the plains may be detected and supported. This research was supported by grants and donations to the Research Training Program. |
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Analysis
of Ceramic Collections from Morona-Santiago, Southeast Ecuador
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Sheena
Ketchum Paulina Ledergerber,
Ph.D. |
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This
project is an analysis of the prehistoric ceramic collections excavated
at two sites in Morona-Santiago, Southeast Ecuador. The analysis showed
that the collections were made with very coarse grit and made with very
diverse methods of decoration; there is also a high percentage of corrugated
sherds present. These findings suggest that there was more than one culture
using the sites and/or that the culture or cultures that constructed the
vessels were not specialized at manufacturing pottery. This research was supported by grants and donations to the Research Training Program. | |||||
Alice
Eve Kennington Internship Endowment
