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Thesis/Dissertation Announcements

Thesis/Dissertation Announcements

Thesis Defense

EXPERIMENTAL TESTS OF THE EFFECTS OF EXOTIC HETEROPHYID METACERCARIAE ON THE SWIMMING ENDURANCE OF SMALL FISH HOSTS


Kelby Clements


Major Advisor: Dr. David Huffman

 

Committee Members: Dr. Timothy Bonner and Dr. Clay Green

 

Thursday, July 5, 2018, 2:00 PM, FAB 130

 An exotic snail from Asia (Melanoides tuberculata) has been introduced into many Texas springs and has become of great ecological concern due to harmful trematode parasites it harbors. The larvae of two of these parasites (Centrocestus formosanus and Haplorchis pumilio) infect many native fishes, some of which are listed species, and have become the most common trematodes in habitats they infest. Many studies have explored the pathology of C. formosanus in different host species, but after 20+ years and hundreds of thousands of dollars, conservation workers are still unable to quantify what effects the parasite is having on the relative fitness of affected fish, meanwhile, the effects of H. pumilio have been virtually ignored. Almost any task most fish must perform in order to compete for food, mates, spawning sites, or to escape from predators, relies on the ability of the fish to swim either at its maximum speed or at lower speeds for sustained time. Anything that negatively affects the swimming performance of such fish will reduce the individual’s ability to thrive. We have developed a device to test the swimming performance of small fish to measure the reduction in performance caused by varying levels of infection with either Centrocestus formosanus or Haplorchis pumilio. Our findings indicate that high levels of infection with Haplorchis pumilio can cause mortality while non-lethal exposure has profound effects on the swimming performance of Cyprinella venusta and the threatened Dionda diaboli. Indeed, we can now specify the percent reduction in swimming performance that can be attributed to infection with H. pumilio. Interestingly, however, C. formosanus had virtually no measurable effects on swimming performance. We conclude that, except for the fountain darter, which is dramatically affected by C. formosanus, more research should be focused on studying H. pumilio as a greater threat to native fishes.


Bio: Kelby is from Gustine, Texas, and moved to San Marcos in 2016 when he joined the Biology graduate program. He earned his Bachelor of Science degree in Wildlife Management from Texas State University in 2012. Kelby enjoys backpacking trips, rock climbing, and winter sports and has plans to move to New Zealand to pursue a career in wildlife conservation.


 

Thesis Defense

Modeling Detection and Density Using Distance Sampling for Three Priority Grassland Bird Species in Texas – Northern Bobwhite (Colinus virginianus), Eastern Meadowlark (Sturnella magna), and Painted Bunting (Passerina ciris)


Name: Anna Matthews

 


Major Advisor: Dr. M. Clay Green

 

Committee Members: Dr. Floyd Weckerly and Dr. Jennifer Jensen

 

Thursday, July 5, 2018, 10:00 AM, Supple 153


Within Texas, three priority grassland species that have experience declines due to loss of native grasslands are the Northern Bobwhite (Colinus virginianus), Eastern Meadowlark (Sturnella magna), and Painted Bunting (Passerina ciris). This 5-year study identified covariates that influence detection, availability, and density for these three species using data collected from 986 surveys across 11 Texas counties. Points were visited once per year from 2013 to 2017 in May and June, and 5-minute point counts were performed using distance sampling protocols. Models were fit using gdistsamp from the package “unmarked” in R. Covariates that influenced detection for Northern Bobwhite were observer, ambient noise, time of day, and Julian date. Detection was higher later in the season, earlier in the morning, and at lower ambient noise levels. Julian date and observer influenced Eastern Meadowlark detection, with detection declining later in the season. Painted Bunting detection was influenced by ambient noise and observer, although the effect of ambient noise appears to be negligible. The proportion of individuals available for detection was influenced by year, showing trends that are likely influenced by precipitation from the preceding year. However, despite this, availability for all species was not influenced by the Palmer Drought Severity Index. Vegetative cover was selected in the top density model for all three species. Native grasslands positively influenced density of Northern Bobwhite and Eastern Meadowlarks, shrubland positively influenced bobwhite and Painted Bunting, and cropland positively influenced bobwhite. Overall, there was high variability in the effect of vegetative cover on density across the three species, indicating that management for one species may ignore vegetative cover needs of other grassland species. Finally, for all species, monitoring should emphasize observer training and attempt to survey only under low ambient noise conditions.


Bio: Anna was born and raised in Dallas, Texas. She left Texas for freezing weather to receive a Bachelor of Science in Fisheries and Wildlife from the University of Minnesota. While there, she discovered a passion for birds, grassland conservation, and education, and she has been fortunate to be able to continue to expand her knowledge and experience in these fields as a graduate student at Texas State University.


Thesis Defense

DETERMINING THE IMPACT OF A CORRELATED SCIENCE AND MATHEMATICS PROFESSIONAL DEVELOPMENT MODEL ON TEACHER LEADERSHIP


Ruby Hernandez


Major Advisor: Dr. Sandra West

 

Committee Members: Dr. Julie Westerlund, Dr. Emily Summers, and Dr. Sandra Browning

 

 

July 5, 2018, 7:30 AM, Norris Room Supple 376


The mathematics and science national standards advocate for educational reform by implementing research-based strategies that includes recognizing the teacher’s critical role in effective instruction. A school’s success can be attributed to recognizing and fostering teacher leadership development. Teachers often feel empowered and become advocates for integration on their campus when they understand how to relate mathematics and science grade-level content in a meaningful way. The purpose of the Correlated Science and Math professional development model used in the Mix It Up project was to better enable science and mathematics integration by classroom teachers. My study aimed to determine the impact of the Mix It Up project on teacher leadership growth in a 2-year cohort (n=23). I investigated teacher leadership using a mixed-methods approach which allowed me to understand if and how teacher leadership growth is occurring. I selected a multiple case study (n=4) to gather enriched details of the process of teachers in MIX progressing into teacher leadership by attaining stage 3, the highest level of leadership, using the NCSM PRIME Leadership Framework. Overall, MIX teachers’ reported they possessed teacher leadership characteristics while 91% reported taking on leadership roles outside their classrooms and stage 3 leaders in my case study attributed their leadership growth to their participation in the MIX PD program. Participants’ reported they were not only implementing and impacting their own students, but were ultimately advocating for science and mathematics integration and the use of general best practices at the district and even state level


Bio: Ruby A. Hernandez is a former high school Biology teacher and plans to return to teaching science in middle or high school to broaden her experience in teacher leader progression. She was born in San Antonio, Texas where she earned her Bachelor of Arts degree in Biology with a minor in secondary education at the University of the Incarnate Word in 2014. She joined the Biology graduate program in Fall 2016.


Thesis Defense

Variation in temperature tolerance of two invasive snails in Texas


Linus Ray Delices


Major Advisor: Astrid Schwalb, Department of Biology, Texas State University

 

Committee Members: Weston Nowlin, Department of Biology, Texas State University

Benjamin Schwartz, Department of Biology, Texas State University

 

Tuesday July 3rd, 2018, 10:00 AM, FAB 130


Invasive species are a major concern for aquatic ecosystems and tropical freshwater snails (Thiaridae) can be very successful invaders. Melanoides tuberculata and Tarebia granifera are two invasive snails in Central Texas that serve as intermediate hosts for several Asiatic trematode parasites of fishes, birds, and other organisms. A better understanding of their temperature tolerances is needed to better predict their spread in Texas and to inform management strategies. Therefore, the goal of my study was to determine the critical thermal minima of these species and to compare temperature tolerances between species, river segments, and different local morphotypes. Survival of snails were monitored in environmental tanks in which temperature was decreased by 0.1°C per hour from 23°C to 10°C. In addition, survival was monitored over time in environmental tanks in which temperature was held constant at 17°C, 15°C, 11°C and 10°C after acclimatization. M. tuberculata showed slightly higher survival at colder temperatures compared to T. granifera. There was no significant difference between local morphotypes of M. tuberculata found in Central Texas, and there were some differences in temperature tolerances of snails between river segments i.e. the upper and lower San Marcos and Guadalupe Rivers. My results show that M. tuberculata can tolerate colder temperatures down to 11°C for a few weeks, which will facilitate their dispersal in rivers of Central Texas farther away from thermally stable spring influenced reaches. Further research is need to examine differences in thermal preferenda and temperature tolerances of snails between rivers.


Bio: Linus grew up in the small town of Viuex-Fort, Saint. Lucia-West Indies. He earned his Bachelor of Science in Biology with a second major in Psychology at Grambling State University. He joined the Biology graduate program in Spring 2015. He is passionate about science and he willingly shared his gifts, talents, keen-eye, great personality and knowledge with others.


Thesis Defense

Impact of Environmental Contaminants on the Threeridge mussel (Amblema plicata) in the Guadalupe River Basin, Texas


Name: Stacey Britton


Major Advisors: Dr. Jessica Dutton and Dr. Astrid Schwalb

 

Committee Members: Clint Robertson (Texas Parks and Wildlife Department- Inland Fisheries)

 

 

July 2, 2018, 10:00 AM, Freeman Aquatic Biology 130


Aquatic pollution has contributed to the significant decline in unionid mussels in North America; however, toxicological studies on Texas unionids are limited. In this study, adult Threeridge (Amblema plicata) mussels were collected from 8 sites within the Guadalupe River basin and the concentration of 8 essential (Co, Cu, Fe, Mn, Mo, Ni, Se, Zn) and 8 nonessential (Ag, As, Cd, Cr, Hg, Pb, Sn, V) trace elements were determined in gill and foot tissues. Additionally, water samples from each site were analyzed for nutrient concentrations. Biomarker analysis (lipid peroxidation, total antioxidant capacity against peroxyl radicals, and protein content) of gill tissue was used to quantify the physiological response of mussels to environmental stressors. Contrary to my expectations, trace element uptake, nutrient concentrations, and physiological stress responses were not necessarily higher at downstream sites. Hg and As concentration in gill tissue were observed to be highest in mussels at the uppermost sites on the San Marcos River and Guadalupe River, respectively. Trace element concentrations in gill tissue did not correlate with general physiological stress biomarkers in mussels; however, higher total nitrogen and total phosphorous concentrations at upstream sites correlated with a) higher lipid peroxidation and lower antioxidant capacity against free radicals, indicating greater oxidative stress, and b) lower protein concentration indicating reduced overall health of adult mussels. Future studies need to investigate the impact of these contaminants on glochidia and juvenile mussels, since early life stages are more sensitive to exposure.


Bio: Stacey has spent the last decade living between Austin and Seattle while pursuing an education in science and raising two bright young girls. Stacey earned her B.S. in Biology with a minor in Chemistry at Texas State University in 2016. She is passionate about science outreach and youth mentorship and hopes to encourage the next generation of environmentalists and ecologists to find their voice.


Thesis Defense

AN INVESTIGATION OF PRESERVICE TEACHERS’ ENGAGEMENT AND PERCEPTIONS OF SCIENCE LEARNING IN OUTDOOR LEARNING ENVIRONMENTS


Sara Salisbury
Major Advisor: Dr. Kristy Daniel 

Committee Members: Dr. Michelle Forsythe and Dr. Julie Westerlund

 

Friday, June 1, 2018, 1:30 PM, SUPP 257


Science education programs that use both formal and informal instruction provide students with more engaging experiences than when only using traditional instruction. However, educators often do not know of, or are uncomfortable with using informal resources. Thus, understanding how educators view and experience science learning in informal environments is necessary for increasing the likelihood that these educators will integrate informal science resources into their curricula. The purpose of this study is to investigate relationships amongst preservice teacher engagement during informal, outdoor learning activities, and perceptions about using informal resources during their future teaching career. During this study, preservice teachers (n=5) took part in a one-day, nature-based fieldtrip as part of a General Science education course. During this fieldtrip, they learned science content and how to teach science in a fieldtrip setting. Using a four-dimensional framework of engagement (i.e., behavioral, cognitive, affective, agentic), I analyzed video, eye-tracking, and interview data to identify moments of engagement, preservice teachers’ perceptions of the fieldtrip, and their integration ideas for using outdoor learning environments in their future teaching career. Overall, participants’ actions indicated their engagement across all four dimensions. Participants thought highly of using outdoor learning environments as potential teaching tools, and could identify some way they could integrate them into future teaching practices. No clear relationship existed between observable engagement actions and preservice teachers’ future integration ideas; However, participants’ overall past experiences with informal learning environments (including the General Science fieldtrip) appeared to largely influence their perceptions and integration ideas. Participants who had no prior teaching experiences drew primarily on their experiences as a student, whereas participants with informal and formal teaching experiences drew upon their experiences as a teacher more than their experiences as a student. Observable engagement actions and interview responses also suggested some participants underwent personally meaningful learning experiences.


Bio: Sara is from New Jersey, and moved to San Marcos in 2016 when she joined the Biology graduate program. She earned her Bachelor’s of Science degree in Environmental Science with a minor in studio art from Allegheny College in 2012. Sara is an avid rock climber, and hopes to someday become a Director of Researcher and Education at an outdoor education institution.


Master’s Thesis Defense

 Bacterial community structure in soils of the oldest agronomic experiment fields in the United States, the Morrow Plots, and of the original tallgrass prairie  


Abirama Sundari Ganesan

 

Major Advisor: Dr. Dittmar Hahn

Committee Members: Dr. Robert McLean and Dr. David Rodriguez

 

Wednesday, May 16, 2018, 10:00 am, Supple 257


New molecular techniques that focus on high throughput DNA sequencing techniques such as 454 pyrosequencing and the MiSeq sequencing platforms revolutionized the field of microbial diversity studies. These techniques are widely used in projects such as the Earth Microbiome Project (EMP), a collective attempt to establish microbial fingerprints in different environments of the planet. Additional applications include studies on long-term effects of crop rotation and different fertilization regimen on bacterial community structure. We tried to build on these studies and assess microbial community structure in the Morrow Plots, the oldest agronomic experimental fields in the United States, and adjacent tallgrass prairie with emphasis on members of the genus Frankia. The Morrow Plots were designed in 1876 on tallgrass prairie soils to evaluate the effects of different cropping systems and soil treatments on crop, and include the oldest continuous corn plots in the world. Illumina-based 16S rRNA V3 amplicon sequencing retrieved total of 26.47 M effective sequences obtained from 44 samples, i.e. 12 soils with different vegetation and fertilization, and 3 to 6 replicates per soil, with 313,695 to 906,328 reads per sample. At a sequencing depth of 300,000 sequences for each sample, Acidobacteria, Actinobacteria, Proteobacteria and Verrumicrobia were the most abundant bacterial phyla present across all soil samples accounting for 74±4% of the reads. Crop rotation increased diversity of the bacterial community, which was also affected by the fertilization regimen. Reads representing frankiae accounted for 0.1 to 1.0% of all reads, with generally higher percentages in fertilized soils. Reads represented frankiae of clusters 1a, 2, 3, and 4, but also a group of frankiae that could not reliably be assigned to a cultured relative. The results provide evidence of long-term establishment of Frankia populations in soils under different management conditions.

Abi received her Bachelor’s degree in Microbiology from the Bharathidasan University, Tamilnadu, India, in 2006, and a Master’s degree in Biotechnology from Bangalore University- Bangalore, India. She started her Master’s degree in Biology in Dr. Hahn’s lab in 2014, applying next generation sequencing methods and the corresponding bioinformatics tools to analyze microbial community structure in soils


Dissertation Defense


Differential selection pressure among duplicated genes in teleosts

Richard John Nuckels, Jr.

Major Advisor: Dana M. García

Committee Members: Dr. Chris Nice, Dr. Noland Martin, Dr. Karen Lewis & Dr. Jeff Gross

 

Friday, May 11, 2018, 10 AM, 153 SUPP


Gene and genomic duplications provide organisms with new genetic material subject to selection. Using myo5, rab11, and rab27 gene families as models, I examined the evolutionary rate differences among duplicated genes and whether selective forces (e.g. purifying selection or positive selection) could be identified in one or both duplicated gene clades. I used phylogenetic and syntenic analyses along with ancestral chromosomal mapping to identify each duplicate. I then analyzed the duplicates using tests for evolutionary selection at the molecular level. Using a branch site-random effects likelihood test, I found evolutionary rate values (ω) to fall into two or three rate classes along at least one branch for one duplicated gene clade for each of the gene trees created. One rate value (ω1) for a percentage of codon sites was close to zero, representing purifying selection. A second rate value (ω2) for a percentage of the codons was much greater than one (ω2 >>>1), signifying positive selection. The two rate classes were present in the teleost myo5bb branch for the motor domain and the cargo binding domain, and two rate classes were present in teleost myo5ba for the cargo binding domain. Also in teleosts, I found two rate classes for the rab11a branch, rab11a1 branch, and rab27bb. Using sequences from 7-10 organisms that diverged from a common ancestor 140-440 million years ago, I found ω values between 0.01 and 0.24 for the whole coding sequence for duplicated genes ranging in size from 200-220 codons. For longer coding sequences (1915 codons), ω ranged from 0.26 to 0.41. I examined the percentage of invariant codons present in each of the gene clades and found the percentage of codons that were invariant to range from 6% for the highly variable neck region of myo5 to more than 30% for some highly conserved duplicated rab11 and rab27 genes and some highly conserved regions for some myo5 duplicates. I identified a highly conserved ω for codons for amino acids that have previously been linked with the functionality of the Myo5 and Rab proteins. These data lead me to infer that the duplicated genes remain functional or have some modified, acquired functionality that remains to be identified.


Bio: Richard John Nuckels, Jr. was born and raised in Texas with brief stints in Wyoming and Colorado. Richard’s research experience began as an undergraduate researcher using zebrafish as a model to understand the evolution and development of pigment cells. His research continued as a lab manager and graduate student using zebrafish as a model for vertebrate eye development. He completed a B.S. in Biochemistry from UT-Austin and an M.S. in Biology from Texas State University. Upon completing his Ph.D. degree, Richard will continue working as a lecturer and lab coordinator at UTSA where he hopes to continue his research while mentoring students in comparative genomics.


Thesis Defense

INFLUENCE OF VARIABLE PLANTING TIME ON THE PRODUCTIVTY OF A CORN-BEAN INTERCROPPING SYSTEM


Sarah Eisenmenger


Major Advisor: Dr. Susan Schwinning

 

Committee Members: Dr. Nihal Dharmasiri, Dr. Ken Mix

 

Thursday, April 5, 2018, 4:30 PM, Supple Norris Room


Intercropping is an agricultural practice in which two or more crops are grown together. It is employed in many countries to increase yields relative to monoculture, especially when crops are grown without fertilizer and pesticide inputs. Previous research has focused on modifying planting densities and spatial arrangements to optimize intercropping yields. This project focused on optimizing the timing of component crop planting as an additional method for improving the overall yield of a corn-bean intercropping system. Corn-bean intercrops typically overyield (meaning they produce more yield grown together than grown separately), either because bean supports the growth of corn through biological nitrogen fixation, or because the two crops have weak competitive interactions and are less suppressed in the intercrop than if they competed intraspecifically in monoculture. I hypothesized that if the bean-corn interaction is facilitative, earlier planting of bean should increase the yields of both crops. Alternatively, if the interaction is competitive, earlier planting of bean would increase bean yield but lower corn yield with little effect on their combined yield. Beans were seeded 20 and 10 days before, simultaneously with, and 10 and 20 days after corn for a total of five intercropping treatments. Additionally, monocultures of each crop with matching planting dates were grown to calculate the yield advantage relative to monoculture. Final yield data supported the second hypothesis; the intercropping yield advantage was not significantly affected by the bean planting offset, but an earlier bean planting provided greater bean yields and slightly lower corn yields. The experiment suggested that, while it is possible tweek corn and bean yields in the intercrop by varying planting times, this does not appear to be an effective method for optimizing combined yield.


Bio: Sarah was born and raised in San Antonio, TX. She enjoys learning about animals, plants, and insects and grew up spending a lot of time outdoors. After starting out as an English major in college, she found that conservation and the environment were more important to her. She graduated from the University of the Incarnate Word in 2015 with a Bachelor of Science in Environmental Science. Sarah then joined the Population and Conservation Biology graduate program in Fall 2015 to study plant ecology. She has a German Shephard mix named Percy and a bearded dragon named Layla.


Thesis Defense

Host plant affiliation and spatial autocorrelation as drivers of genetic differentiation among populations of a regionally host-specific insect herbivore


Name: Amanda L. Driscoe


Major Advisor: Dr. James R. Ott

 

Committee Members: Dr. Chris C. Nice and Dr. Noland H. Martin

 

Monday, April 2, 2018, 1:00 PM, Norris Room


Disentangling the processes responsible for structuring patterns of biodiversity at all spatial scales challenges biologists as such patterns represent evolutionary and ecological processes coupled with spatial autocorrelation among sample units. The phytophagous insect, Belonocnema treatae (Hymenoptera: Cynipidae) exhibits regional specialization on three species of live oaks throughout its geographic range across the southern USA. Here I ask whether populations of B. treatae affiliated with each host plant exhibit genetic differentiation that parallels host plant phylogeography while controlling for spatial autocorrelation among sampling locations. I used next-generation genotyping-by-sequencing of 1,219 B. treatae collected from 58 sites distributed across the geographic ranges of the three host plants to identify 6,987 common, and 44,390 rare, single nucleotide variants. Population genomic structure was then investigated using a hierarchical Bayesian model to assign individuals to genetic clusters and estimate admixture proportions. To control for spatial autocorrelation when investigating the role of host plant affiliation in determining patterns of among-population genetic differentiation, Distance-based Moran’s eigenvector maps was used to construct regression variables summarizing spatial structure inherent in the sampling design. Redundancy analysis (RDA) incorporating these spatial variables was then used to simultaneously examine the roles of host plant affiliation and spatial autocorrelation in determining patterns of among-population genetic differentiation. RDA confirmed host-associated linages of B. treatae in the eastern portion of the species’ range and clinal host-associated lineages in the west, independent of spatial autocorrelation. These results suggest a linkage between the history of genetic differentiation among host plants and genetic differentiation of the host-associated herbivore populations.


Bio: Amanda earned her Bachelor’s of Science in Animal Science at University of Minnesota, Twin Cities. She joined the Population and Conservation Biology graduate program in Fall 2015.


Thesis Defense

CONSEQUENCES OF LONG-TERM CHANGES IN FISH COMMUNITY STRUCTURE ON ECOSYSTEM FUNCTIONING IN A SUBTROPICAL SPRING-FED RIVER


Aine Carroll


Major Advisor: Dr. Weston Nowlin 

 

Committee Members: Dr. Thom Hardy, Dr. Josh Perkin

 

Monday, April 2, 2018, 12:00 PM, FAB 130


Ecologists have examined and debated about the relationship between biodiversity and ecosystem functioning but have in general found that the functional roles of species within communities affect ecosystem functioning. Biological invasions are globally pervasive and can have potentially deleterious effects on ecosystems because some non-native taxa can establish dominance in biomass or abundance and have a detrimental impact on their introduced environment. Although the effects of non-native taxa have been examined for decades, few studies have utilized a longer-term perspective (> 10 years) to assess how non-native taxa affect ecosystem functioning. In this study, I examined long-term changes in fish community composition in the spring-influenced upper San Marcos River (central Texas, USA) and its ecosystem functioning implications, specifically how temporal changes in the composition and diversity of the fish community were related to changes in the rates and ratios of dissolved inorganic N (NH4+) and P (PO43-) recycled by the fish community and the sequestration of nutrients into fish biomass. I assembled a 76-year data set (1938 – 2016) of fish collections for the upper San Marcos River and linked it to contemporaneous estimates of species-specific nutrient content and dissolved nutrient excretion rates from the upper San Marcos River. Analysis of the fish community indicated three distinct time periods with notable shifts in fish community composition between time periods: 1938 – 1959 (Period I), 1960-1989 (Period II), and 1990 – 2016 (Period III). Patterns in occurrence-weighted biomass indicated that there were substantial shifts in which species had the larger contribution to community-wide biomass (as C, N and P) of the entire fish community, with the proportional contribution of non-native and non-spring associated fishes being the highest in Period II. However, the proportional contribution of non-native and riverine-associated fishes to the community-wide dissolved P and N recycling rates increased across the three periods. This study indicates that, although the upper San Marcos River contains a relatively diverse community containing a large number of native taxa, the relative importance of non-native species in ecosystem functioning has generally increased over time.


Bio: Aine is from Dallas, and moved to Austin in 2007. She earned her bachelor’s degree in English Writing with a minor in Environmental Science and Policy from St. Edward’s University in 2011. She joined the Aquatic Resources graduate program in Fall 2015.


Thesis Defense

Host Plant and Spatial Influences on the Natural Enemy Community Structure of a Host Specific Herbivore


Name: Robert Busbee


Major Advisor: Dr. James Ott, Department of Biology, Texas State University

 

Committee Members: Dr. Chris Nice, Department of Biology, Texas State University, Dr. Noland Martin, Department of Biology, Texas State University

 

Monday, April 2, 2018, 10:00 AM, Supple Science Building, Room 257


Both environmental variation and spatial autocorrelation play roles in structuring communities at all spatial scales. However, untangling the respective contributions of these sources of variation represents a long-standing, complex, and methodologically ever-evolving question for community ecology. Here I investigate the structure of the insect natural enemy community centered on galls produced by Belonocnema treatae (Hymenoptera: Cynipidae) on the leaves of its host plants across the gall former's geographic range while controlling for spatial autocorrelation among sample sites. Belonocnema treatae exhibits regional host plant specialization across the southern US on three live oak species, Quercus fusiformis (Qf), Q. virginiana (Qv), and Q. geminata (Qg). I sampled the natural enemy community at 118 sites by rearing natural enemies that emerged from galls collected at each site. I identified 32,722 natural enemies representing ≥30 taxa from 126,812 galls. I hypothesized that richness and diversity on Qv would exceed that on Qf and Qg since the geographic range of Qv bridges that of Qf to the west and Qg to the east. Contrary to my hypothesis one-way ANOVA followed by a Tukey’s HSD showed that both richness and Shannon-Wiener diversity was greatest on Qf. To disentangle the role of host plant affiliation from spatial autocorrelation among sample sites I conducted a Redundancy Analysis (RDA). I first used Principal Coordinates of Neighbor Matrices (PCNM) to generate explanatory variables representing orthogonal aspects of spatial structure within the sampling frame. The set of PCNM vectors that were significant were then included in a RDA along with the host plant species from which each natural enemy was reared to examine the respective roles of host plant affiliation and spatial structure in determining abundance and species composition of the natural enemy community. This study establishes a significant role for both alternative host plants and geography in structuring the diversity of the natural enemy community of B. treatae and illustrates the advantages of the PCNM & RDA approach.


Bio: Robert earned his Bachelors of Science in Ecology and Evolutionary Biology at Angelo State University. He joined the Population and Conservation Biology graduate program in Fall 2015.


Thesis Defense

Assessing seasonal diets of waterbuck (Kobus ellipsiprymnus) in central Texas


Kaitlin Lopez


Major Advisor: Dr. Thomas R. Simpson

 

Committee Members: Dr. Dittmar Hahn (Co-Chair), Dr. David Rodriguez, Dr. James Gallagher (Texas Parks and Wildlife)

 

Monday, April 2, 2018, 9:00 AM, Supple 153


It is important to understand how different species use food resources when developing wildlife management strategies. This is particularly relevant in Texas where exotic ungulates are frequently stocked outside their native range with other species with which they did not coevolve. To date, no food habit studies have been conducted in Texas for waterbuck (Kobus ellipsiprymnus), a large antelope native to Africa. I investigated the seasonal diets of waterbuck located on Mason Mountain Wildlife Management Area in Mason County, Texas from June 2016 to March 2017. The objectives of my research were to 1) determine the seasonal diets of waterbuck by using microhistological analysis to identify and quantify plant fragments found in fecal material, 2) determine if waterbuck forage selectively, and if so, which foods were used more or less than their availability, 3) use DNA analysis to identify plant DNA extracted from fecal material, and 4) compare the results from both diet analysis techniques. In each meteorological season, I collected 20 freshly deposited fecal samples for diet analyses. To determine if waterbuck were selectivity foraging, I conducted vegetation surveys simultaneously with fecal sample collection to estimate availability of plants. I used the Daubenmire method to quantify available herbaceous vegetation and the line-intercept method to quantify available woody vegetation at 10 different points occupied by waterbuck. DNA analysis targeted the c to h region of the chloroplast trnL (UAA) intron. DNA was not successfully amplified and sequenced from fecal samples. Using microhistological analysis I quantified 47 unique plant species in the diet of waterbuck. To construct the diet, I looked at the number of fragments detected for each species compared to the total number of fragments examined (N = 2000, 500 per season). To determine if plants were utilized more than their estimated availability I performed a log-likelihood chi square test. To further determine forage selectivity, I used Manly’s alpha index of selectivity and constructed 95% confidence intervals around estimate proportions of use for each species consumed. In all seasons, plants were not used proportional to their availability in the environment and waterbuck actively selected their food resources. The bulk of the diet consisted of grasses, most of which occurred in wetlands. My results suggest that resource competition between waterbuck and upland grazers such as gemsbok, sable antelope, and scimitar-horned oryx is minimal. However, competition needs to be considered when stocking waterbuck with cattle or other grazers that regularly utilize riparian species.


Bio: Kaitlin was born in Maryland but moved to McKinney, Texas at the age of two where her passion for animals, bugs, and all things outdoors flourished. In December 2014, she graduated cum laude from Texas State University with her Bachelor of Science degree in Wildlife Biology. Following a brief break from academia, Kaitlin returned to Texas State University to join the Wildlife Ecology graduate program in Fall 2015.  


Thesis Defense

Paleoclimate of the Two Medicine Formation based of leaf physiognomy


Ann Marie Prue


Major Advisor: Dr. Gary Upchurch

 

Committee Members: Dr. Karen Chin (University of Colorado), Dr. Julie Westerlund, and Dr. Noland Martin

 

Friday, March 30, 2018, 10:00 AM, Supple 326


In the last 50 years, methods to study ancient warm climates, like those of the Cretaceous, have yielded new information on climates and their interaction with flora and fauna. One of the effective ways to reconstruct paleoclimates in terrestrial environments is to study the external features of plant leaves, or leaf physiognomy. Features of leaves from different climates have been correlated to mean annual temperature (MAT) and mean annual precipitation (MAP). There are several methods to determine paleoclimates that are based on the modern-day correlations between leaf features and climate parameters. These methods include the univariate methods of leaf margin analysis (LMA) and leaf area analysis (LAA), and the multivariate methods of Climate Leaf Analysis Multivariate Program (CLAMP) and Digital Leaf Physiognomy (DiLP). This study uses these paleoclimate proxies to study the Two Medicine Formation, a famous formation in northern Montana that contains both dinosaur and paleobotanical remains. In addition, the research examines the congruence of different physiognomic methods with each other and with other climate proxies for the Two Medicine Formation and surrounding formations of similar age. This study concludes that the univariate methods give generated temperature estimates that are too low, and a precipitation estimate that is too high. Of the two multivariate methods, CLAMP gives slightly lower temperature estimates and has inconsistencies based on classification of leaf features. DiLP, on the other hand, gives more reasonable estimates based on congruence with other paleoclimate proxies. However, the DiLP image processing of the leaves is more complex and time consuming than that of the other methods. In order to cut the leaf image processing time, a new modified technique of doubling the leaf halves from partial fossil specimens was implemented in this study. Preliminarily results from the doubling halves technique indicates that climate parameter estimates are nearly the same as those described in the original DiLP method.


Bio: Ann Marie is a born and raised Cheesehead from Green Bay, WI. She got her bachelor’s degree in Geology and a minor in Horticulture from the University of Wisconsin-River Falls in 2015. While participating in UNAVCO’s NSF funded summer internship, RESESS, she was introduced to using fossilized leaves to infer paleoclimate by Dr. Gary Upchurch. She joined Dr. Upchurch’s lab in the fall of 2015 to work on a project that combined her two passions: rocks and plants. Upon graduating, Ann Marie plans on returning to Wisconsin to weed her gardens, whack rocks, and join the work force. She eventually plans to continue her education to fulfill her dream of getting a PhD. in Geology.


Thesis Defense

Prevalence of endoparasitic helminths of the small Indian mongoose (Herpestes auropunctatus) on the island of Puerto Rico


Name: Jose A. Martinez III


Major Advisor: Dr. Iván Castro-Arellano

 

Committee Members: Dr. Thomas R. Simpson (Co-Chair), Dr. David Huffman

 

Friday, March 30, 2018, 1:00 pm, Supple 153


The small Indian mongoose (Herpestes auropunctatus; heretofore mongoose) has been widely introduced to islands around the world as a biological control agent. Species targeted for control were various rodents and venomous snakes. Follow-up research has been conducted on the mongoose’s role as a potential reservoir of diseases that might affect man and economically important animals. However, most of previous studies have focused on detecting rabies and leptospirosis, with reports related to endoparasitic helminthes being largely incidental. The only study conducted on Puerto Rico reported no endoparasitic helminths from an examination of 210 mongoose visceral organs. From May 22 to August 12, 2015 I trapped mongoose from 5 sites (cattle farms) on Puerto Rico and conducted standard necropsy techniques to survey for endoparasitic helminthes in the viscera. Each site was trapped for a minimum of 2 weeks, logistics and farm operating hours permitting. Each transect consisted of approximately 50 Tomahawk live traps (20x7x7”, Model #204, Tomahawk Live Trap Co, Hazelhurst, WI). Transect checks took place daily starting at 08:00 for regular intervals of 2 hours (depending on heat every hour) until approximately 1700. Using standard necropsy techniques, the visceral organs and tissues collected from 60 mongooses were: Lungs with attached trachea, heart, liver with attached gallbladder, gastrointestinal tract (esophagus to rectum) with associated mesenteric tissues, and bladder. There were no observable signs of parasitism in the major organs (Heart, liver, lungs, bladder, and gallbladder). My examinations of the gastrointestinal tracts yielded two species of nematodes and one Acanthocephalan. The nematode Skrjabinocapillaria caballeroi was found infecting 65 percent of mongoose stomachs while Physaloptera spp. were recovered from 18 percent of gastrointestinal tracts. The Acanthocephalan Oncicola venezuelensis was recovered from the greater and lesser omentum, fascia of the skin and muscle, small intestine tissues, and the connective tissues of the liver to the diaphragm of 36.6 percent of examined mongooses.


Bio:Jose was born in California but has moved over 30 times since including living and graduating High School in Italy. In 2002 he joined the United States Marine Corps where a passion for wildlife and the outdoors was deeply fostered. In December 2013, he graduated from Texas State University with his Bachelors of Science in Wildlife Biology. Following a short break in South Africa working with large African predators, Jose returned to Texas State and joined the Wildlife Ecology graduate program in Fall 2014.


Thesis Defense

Roosevelt elk response to a newly available foraging pATCH


Aaron McGuire


Major Advisor: Dr. Floyd Weckerly

 

Committee Members: Dr. Clay Green, Dr. Mark Ricca

 

March 30, 2018, 11:00, Supple 153


According to optimal foraging theory, herbivores will use a new foraging patch intensely to become familiar with a new resource. To better understand how herbivores incorporate new habitat into their home range, I examined use by a Roosevelt elk (Cervus elaphus roosevelti) herd in Redwood National and State Parks, California, that was recently given access to a nearby, new foraging patch, the cattle pasture. Cattle and predators, both of which can negatively affect elk spatial patterns, also used the cattle pasture. My study objectives were to examine monthly elk use in the cattle pasture, assess cattle and predator influence on herd use of the pasture, analyze summer and winter movement patterns to assess if forage biomass was more limited in one season, and determine if the herd was using the cattle pasture intensely to become familiar with the resources. I placed six infrared, motion sensitive cameras throughout the cattle pasture from August, 2016, to November, 2017. I followed the herd from dawn to dusk, recorded elk activity, movement (step length), and forage biomass in January, 2017 and 2018. Herd movement was also recorded in July, 2017. I found avoidance between elk and cattle and elk and predators at short temporal and small spatial scales in the cattle pasture. Step lengths were similar between summer and winter months. The herd used the cattle pasture more in January, 2018, than in January, 2017. My finding were inconsistent with optimal foraging theory.


Aaron grew up in Roswell, New Mexico where he found his passion for wildlife and working in the outdoors. He graduated from New Mexico State University in 2010 with his bachelor’s degree in Fish, Wildlife, and Conservation Ecology with a double emphasis in wildlife and fisheries. After getting his bachelor’s degree, Aaron moved to Northwest Wyoming where he worked for the Wyoming Game and Fish Department as a fisheries technician, a wildlife damage technician, and a hunt management coordinator. In 2014, Aaron moved to Bozeman, Montana where he worked for Montana State University as a fisheries technician and a wildlife capture technician. He also worked for Montana Fish, Wildlife, and Parks as a wildlife disease technician and a hunt management coordinator. Aaron moved to San Marcos in the fall of 2016 to pursue his master’s degree in wildlife ecology. Aaron plans to move back up north and become a regional wildlife management biologist for a state agency.


 Thesis Defense

Population Viability of Reddish Egrets (Egretta rufescens) in Texas: A System Dynamics Approach to Conservation and Management of North America’s Rarest Heron


Sarah Durham


Major Advisor: Dr. Clay Green

Committee Members: Dr. Floyd Weckerly and Dr. Steve DeMaso

March 28, 2018, 11:00am, Norris Room


Reddish egrets are a threatened waterbird species that inhabit the Gulf Coast of the U.S. and Mexico, as well as, the Bahamas, Cuba, the Mexican Pacific Coast, and the Yucatan peninsula. The plume trade of the late 1800s drastically reduced global population numbers of reddish egrets. By the 20th century, the species was decimated and possibly extirpated in many parts of its range. While much of the historical range has been recolonized, the reddish egret remains North America’s least abundant heron species. An estimated one-third to one-half of the global reddish egret population occurs in the United States, with Texas having approximately 75% of the breeding pairs. While egret population numbers may be stable or increasing in portions of the range, many factors continue to threaten the persistence of the species. Population viability analyses (PVAs) are a common method of predicting a species’ persistence into some future time. The purpose of developing a population viability analysis for E. rufescens is to identify possible factors impeding the growth of Texas populations. By assessing the relative threat of each contributing factor and identifying vulnerable life stages, a robust PVA can estimate how different management actions may affect population demographics. I found that four-year-old female survivorship during the non-breeding and breeding seasons to be the most influential model parameters. My findings are similar to other studies that have found adult survivorship to be the most influential factor to population growth in other long-lived avian species that mature late. Additionally, I found that both the total and breeding populations are projected to remain stable over the next 50 years. While these results are encouraging, it is important to note that the model does not incorporate habitat or spatial information. These findings suggest that management actions focusing on increasing adult survivorship, such as habitat protection, would be most beneficial to population growth and persistence of reddish egrets in Texas.


Bio: Sarah grew up in the rough and tumble corn fields of central Illinois. She moved to Texas in 2011 and began the Wildlife Biology undergraduate program at Texas State University in the Fall of 2012. Sarah graduated summa cum laude from Texas State University in 2015. She began her master’s work in the Fall of 2015 studying reddish egrets. Her hobbies include knitting and cats.


Thesis Defense

Exploring tradeoffs in alternative life history strategies


Amara Lee Garza


Major Advisor: Chris C. Nice, Department of Biology, Texas State University

Committee Members: Jim R. Ott, Department of Biology, Texas State University

Susan Schwinning, Department of Biology, Texas State University

Friday, March 23, 2018, 9:00 AM, Supple Science Building, Room 153


The evolution of gregarious feeding is an intriguing problem in ecology. It occurs in many phytophagous insects and typically coincides with eggs lain in large clutches. Despite many benefits to gregarious feeding, including accelerated larval growth rates, not all species feed gregariously suggesting disadvantages to gregariousness. To investigate the advantages and disadvantages, I studied a system of two sympatric, congeneric butterfly taxa that employ drastically different oviposition and larval feeding strategies. The Emperor butterflies both lay eggs on Hackberry trees (Celtis laevigata, C. reticulata); the Hackberry Emperor (Asterocampa celtis) lays a single egg and caterpillars feed alone, while the Tawny Emperor (A. clyton) lays a large clutch and caterpillars feed gregariously. To explore whether gregarious feeding drives clutch size differentiation while simultaneously filling in natural history information on Asterocampa butterflies this research addressed the following questions: 1) Is there a difference in emergence in terms of relative abundance of Asterocampa between sexes or species? 2) Do Asterocampa species have an oviposition preference between Celtis (Hackberry) host plants? 3) Do Asterocampa larvae experience enhanced performance in gregarious feeding groups? I predicted that the advantage of gregarious feeding would be realized for A. clyton, where females lay large clusters of eggs. Fruit baited traps were used to capture females. Phenological variation in relative abundance was analyzed with partial correlation coefficients. Female oviposition preference was assessed with a choice experiment with leaves of both host trees. Caterpillar group sizes were manipulated across the two host plant species. The group sizes approximated ranges from nature. Caterpillar performance was measured by average weight gained and proportion of caterpillars reaching their second instar. Oviposition preference was quantified using a Bayesian hierarchical model. Caterpillar performance was analyzed using an ANOVA in R. There were no differences in relative abundance across time. Females of both butterfly species preferred to oviposit on C. laevigata. I found significant differences in weight gained between group size treatments and caterpillar species but not between host species. I also found a significant difference in proportion reaching second instar between group size treatments, caterpillar species and host species. My results indicate a disadvantage to being gregarious and demonstrate that solitary feeding can enhance caterpillar performance; thus, the predicted benefits of gregariousness for caterpillar performance were not observed. The advantages of gregarious feeding were not realized in terms of caterpillar performance but might be related to defense against natural enemies.


Bio: Amara earned her Bachelors of Science in Biology at Saint Edward’s University. She joined the Population and Conservation Biology graduate program in Spring 2014.


Dissertation Proposal Defense

 

Competition of Frankia populations for nodulation and development in soils

 


Spandana Vemulapally
Major Advisor: Dittmar Hahn

Committee Members: Mark Paschke (Colorado State University)

Jeffrey O. Dawson (University of Illinois, Urbana-Champaign)

Robert McLean

David Rodriguez

 

Monday, March 5, 2018, 1:00 pm, Norris Room


Actinorhizal plants exist in symbiotic associations with root-nodule forming Gram-positive actinobacteria of genus Frankia. These filamentous heterotrophic bacteria provide the plants with reduced nitrogen resources through nitrogen fixation. Recent studies in our lab using molecular tools like qPCR and Illumina sequencing to quantify Frankia populations in soil and root nodules suggested large differences between detectable Frankia populations in soil and those in root nodules. The data suggested that root nodule formation was not a function of abundance or relative diversity of specific Frankia populations in soils. Our hypothesis was that the differences were due to alternative traits of the Frankia populations, one of which could be competition between strains in which one strain outcompetes the other for nodule formation even at low abundance. An alternative hypothesis was that it could be growth appearance, in which one strain producing many small fragments with small numbers of cells could provide more nodulation units than another one developing few large colonies with comparatively more cells. We took advantage of the availability of specific pure cultures representing individual clusters or sub-clusters within the genus Frankia and then developed specific quantification methods that allowed us to distinguish and quantify these strains after inoculating in different concentrations and combinations in microcosm studies under controlled conditions. Quantification and characterization of populations in soil and rhizosphere as well as in nodules of the host plant species were done using qPCR and in situ hybridization techniques targeting specific Frankia populations. Using the same techniques, we were also studying host plant effects on competition for nodule formation by representative strains of different Frankia clusters.


Bio: Spandana Vemulapally was born in Andhra Pradesh, India. She graduated with a Master of Science degree in Biotechnology from Texas Tech University in 2012 and a Master of Science degree in Biomedical Sciences from Texas Tech University Health Sciences Center in 2015. She enrolled in the PhD program at Texas State University in Spring 2016.


Dissertation Defense

Plant effects on the dynamics of Frankia populations in soil


Seifeddine Ben Tekaya

Major Advisor: Dittmar Hahn

Committee Members: David Rodriguez

Robert McLean

Jeffrey O. Dawson (UIUC)

Mark Paschke (CSU)

 

March 5, 2018, 8 am, Supple 153

 


Frankiae are slow growing actinobacteria that are able to form root nodules with some woody non-leguminous plants. Studies on the ecology of these bacteria are hampered by difficulties to isolate them into pure cultures which was a prerequisite for quantitative analyses in the past. We have therefore focused on the development of molecular approaches that allowed us to retrieve quantitative data from environmental samples unbiased by the limitations of culturability. A first objective of the current study was to develop qPCR based methods to distinguish groups within the genus and quantify their populations in soil. Additional attempts were made to distinguish and quantify typical, nitrogen-fixing frankiae from atypical, generally non-nitrogen fixing frankiae. Both SybrGreen- and Taqman-based qPCR methods were subsequently evaluated for the quantification of these populations in different soils. These methods are then used to study long term effects of agricultural management practices on abundance and diversity of frankiae. Data from these analyses were contrasted with Illumina sequencing data. Both qPCR and Illumina sequencing methods were also applied in analyses of microcosm experiments aiming to investigate the effects of plants species on indigenous populations of Frankia and relate abundance/diversity in soils to root nodule populations.


Bio: Seif was born in Carthage, Tunisia, in May 13, 1984. He completed a BS degree in Biological Sciences at the University of Tunis el Manar in 2007, and earned an MS degree in microbiology from the same university with a research thesis that focused on the diversity of ascomycetes in high saline lakes in 2009. In 2014, he joined the Ph.D. program in Aquatic Resources at Texas State University.


Dissertation Proposal Defense

Consequences of Artificial Light at Night on the Physiology and Behavior of Amphibians

Zachery R. Forsburg

Major Advisor: Caitlin R. Gabor, Department of Biology, Texas State University, USA

Committee Members:
Andrea Aspbury, Department of Biology, Texas State University, USA
Mar Huertas, Department of Biology, Texas State University, USA
Jenny Ouyang, Department of Biology, University of Nevada, Reno, USA
Edward Narayan, Department of Natural Sciences, Western Sydney University, Australia

Wednesday, February 28, 2018, 4:00 PM, Supple Science Building, Room 376


Artificial light at night (ALAN) is defined as artificial light that alters the natural light dark patterns in ecosystems. ALAN is a growing problem globally as 40% of the World’s population lives in areas continually illuminated. ALAN can have a suite of effects on community structure and is a driver of evolutionary processes. ALAN has been shown to affect the behavior and physiology of many taxa, yet research on how ALAN may affect behavior and physiology in amphibians, the most imperiled vertebrate class, is lacking. ALAN may contribute to stress and ultimately declines of amphibian populations, particularly in urban areas. I propose to examine, through laboratory and semi-natural mesocosm studies, if ALAN is contributing to physiological stress and altering behaviors in amphibians. I will also explore whether exposure to ALAN is affecting growth and survival in tadpoles and potential carry-over effects of ALAN exposure on juvenile frogs. Further, in a mesocosm setting, I will investigate if other variables such as predation and pesticide exposure have synergistic effects with ALAN by measuring growth, behavior, and physiology in tadpoles. Employing a non-invasive water-borne hormone collection protocol will facilitate a repeated measures protocol allowing me to use a reaction norm approach to analyze how hormonal and behavioral traits change over time and environmental gradients. Together, this research will provide new insights into the consequences of ALAN on amphibian populations, and if hormonal responses can evolve in response to rapid human change such as light at night.


Bio: Zach Forsburg grew up in Central Pennsylvania and earned his B.S. and M.S. in Biology from Shippensburg University. Seeking warmer weather, Zach moved to South Florida after graduate school to work at Archbold Biological Station in Venus, Florida, where he collected data on habitat use and movements of gopher tortoises and federally threatened Eastern indigo snakes. Zach was a member of the 2015 Florida Wildlife Corridor Expedition team, a 70-day, 1,000-mile, journey across Florida to bring awareness of conservation needs in Florida. He ended his 6 years at Archbold as the Director of Development and began his PhD studies in 2015. He hopes to be the next Richard Archbold.


Dissertation Proposal Defense

 

Factors influencing riverine community structure of aquatic organisms: implications for imperiled species management


David S. Ruppel
Major Advisor: Timothy H. Bonner, Department of Biology, Texas State University

Committee Members;

Noland H. Martin, Department of Biology, Texas State University

Kenneth Ostrand, U.S. Fish and Wildlife Service, San Marcos, Texas

Jim A. Stoeckel, School of Fisheries, Aquaculture, and Aquatic Sciences, Auburn University

Joseph A. Veech, Department of Biology, Texas State University

 

Thursday, February 15,2018, 2:00 PM, Freeman Aquatics Building, Room 102

 


Aquatic communities are structured by selection, drift, dispersal, and speciation processes. Processes collectively interact to generate a diversity in community patterns among riverscapes. Aquatic community patterns and processes can be disrupted by anthropogenic alterations, such as changes in water quality and quantity, introductions of exotics species, and habitat fragmentation. The common theme among the chapters of my dissertation is the identification of patterns that aid in understanding processes (e.g., selection, drift, and dispersal) and conservation status (resiliency, representation, and redundancy) of riverine communities and species. Dissertation chapters will address gaps in existing information necessary to inform individual, population, and range-wide responses to natural and anthropogenic influences using the USFWS Special Status Assessment (SSA) framework for establishing species viability through demonstrated or predicted redundancy, representation, and resiliency. Chapter I will be a fish-habitat community assessment within the upper Red River of Texas and Oklahoma (2-year survey). Chapter II and III will assess life history characteristics and factors influencing instream movement of USFWS candidate species (Prairie Chub), a SGCN species (Red River Shiner), and an endemic species (Plains Killifish). Chapter IV will be mussel distributions and habitat associations, including habitat assessments for several USFWS candidate species, within the Colorado River. Unique contribution of my work is the application of the theoretical community ecology framework to understanding redundancy, representation, and resiliency of local systems with multiple species of conservation concern.


Bio: David was born in Saginaw, Michigan but lived in the quaint town of Ishpeming in Michigan’s upper peninsula for most his childhood. He graduated cum laude with his B.S. in Zoology from Northern Michigan University in 2012. David completed his M.S. in Aquatic Resources in August 2014 studying the effects of instream flow recommendation on larval fish diets in the San Antonio and Guadalupe Rivers. He began as a PhD student in 2015 and plans to complete his PhD in December 2018. Long term goals include obtaining a tenure-track professor position.


Dissertation Proposal Defense

Biofilm Growth and Control in Spaceflight


Starla Thornhill


Major Advisor: Dr. Robert “Bob” McLean Texas State University

 

Committee Members: Dr. Cheryl Nickerson Arizona State University

Dr. C. Mark Ott -NASA Johnson Space Center

Dr. David Rodriguez Texas State University

Dr. Dana Garcia – Texas State University

 

February 02, 2018, 8:00 Am, Norris Conference Room, Supple 376


Biofilm formation in microgravity is largely understudied. At this time, only a few studies of biofilms in microgravity have been published, and in those cases only monoculture biofilms. Environmental biofilms, including those on spacecraft, are polymicrobial communities. The Potable Water Dispenser on the International Space Station (ISS) is host to a persistent biofilm that is resistant to long-term disinfection. Since biofilms cause microbiologically-induced corrosion and release cells into the environment, their presence is a potential risk to the ISS crew. To investigate mixed species biofilms in microgravity environments, biofilms of Escherichia coli and Pseudomonas aeruginosa will be grown in coculture on stainless steel coupons using microgravity modeling high-aspect ratio vessels (HARVs). These bacteria can be differentiated using inserted mCherry (into E. coli) and gfp (into P. aeruginosa) genes. Biofilm structure will be analyzed using confocal microscopy and species composition by qPCR. Boric acid, a biofilm dispersant agent, will be investigated in concert with disinfectants currently in use on ISS to determine their disinfection capability. Microbiologically-induced corrosion on stainless steel will also be investigated using analytical electron microscopy and energy dispersive X-ray spectroscopy. Additionally, an experiment investigating growth, Ag-based disinfection, and corrosion will be sent to ISS for investigation in true microgravity. While in flight, biofilms will be analyzed using epifluorescence microscopy and post-flight analytical electron microscopy. This will allow for a better understanding of the growth and treatment of biofilms on ISS, providing a safer environment for long-term habitation of humans in spaceflight.


Bio: Starla Thornhill earned her BS (Microbiology) and MS (Biology) at Texas State University in 2014 and 2016, respectively. She grew up in Austin, TX. She loves cats and video games. Her research interest is microbiology in spaceflight. She won People’s Choice Award at the University Final 3MT Competition in 2017.

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  • Spring 2018