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Thesis/Dissertation Announcements

Current schedule of defenses

Dissertation Defense

The Natural History, Ecology, and Molecular Detection of JollyVille Plateau Salamanders (Eurycea Tonkawae)

Name: Zachary C. Adcock

Major Advisor: Dr. Michael R.J. Forstner

Committee Members: Drs. James D. Nichols, Benjamin A. Pierce, David Rodriguez, and Benjamin F. Schwartz

Location: Tuesday, 18 October 2022, 8:30am, Norris Room, Supple Science Building

Or join Zoom meeting: Meeting ID 998 2457 1045, Passcode: Adcock


The Edwards-Trinity Aquifer system of central Texas provides habitat for approximately 15 species of endemic plethodontid salamanders in the genus Eurycea. These taxa are aquatic and inhabit springs and spring-fed creeks in addition to subterranean water in alluvium and the pores, conduits, and caves of eroded karst limestone. Many of these taxa are protected by the U.S. Fish and Wildlife Service (USFWS) because of their small geographic distributions on a landscape undergoing rapid development. Jollyville Plateau Salamanders (E. tonkawae) occur in the Austin, Cedar Park, and Round Rock metropolitan areas of Travis and Williamson counties, Texas, and this species was listed as federally threatened in 2013 because of concerns for habitat loss, degraded water quality, and reduced water quantity due to urbanization. At the time of listing, the USFWS had to designate critical habitat units (CHUs) and identify important habitat components with only a single peer-reviewed, ecological study published for this species. Therefore, the intent of my dissertation was to inform E. tonkawae conservation, management, and policy in a series of chapters that investigate the species’ reproductive biology, ecology in surface habitat, and detection utilizing molecular techniques. First, I modeled the reproductive phenology of E. tonkawae and provided the first estimates of clutch size. Eurycea tonkawae exhibited seasonal reproduction with oviposition occurring in winter months and an average potential clutch size of less than ten oocytes. Second, I estimated E. tonkawae population parameters in relation to distance from a spring outlet and compared the results to the federal CHU. Eurycea tonkawae relative abundance and relative density decreased with increasing distance from a spring outlet, but individuals also occurred outside of the federal CHUs at some sites. Importantly, the downstream extent of E. tonkawae and the rate of change in relative abundance and relative density were heterogenous among study sites which is incongruent with the uniform federal CHU designation. Third, I estimated E. tonkawae relative abundance among cover object types to assess the USFWS’s description of optimal habitat. Eurycea tonkawae utilized all available cover types, and relative abundance was higher in a cover type the USFWS considers suboptimal habitat (i.e., vegetation) compared to optimal habitat (i.e., rocks). Fourth, I estimated E. tonkawae relative density in relation to multiscale habitat parameters to determine which aspects of habitat influenced salamander density in headwater creeks. Eurycea tonkawae relative density was negatively influenced by the presence of predatory, centrarchid fishes, and this habitat component was more influential than several micro-scale ecological variables previously considered important for this species. Finally, I developed, validated, and applied an eDNA assay using quantitative PCR (qPCR) to provide a survey option for habitats where it is difficult or not practical to visually detect E. tonkawae and other members of the Septentriomolge clade. Estimates of the probability of detection and probability of occurrence were similar between eDNA surveys and concurrent visual encounter surveys demonstrating that eDNA has the potential to be an effective survey technique for these species.


Zach is from Cedar Hill, Texas. He earned a B.S. from the University of Tampa and a M.S. from the University of South Florida. He has worked in the field of endangered and threatened wildlife ecology for the better part of the last 20 years in both Florida and Texas. He is currently a Senior Ecologist at Cambrian Environmental in Austin where he is continuing research on central Texas Eurycea salamanders. His wife, Michelle, is also a wildlife biologist in the Ph.D. program at Texas State University and they have two sons, Davis and Coleman, who are far more wild than any animal they have ever had to study.


Thesis Defense

 Environmental Factors Influencing the Spread and Successful Invasion of Arundo donax in Central Texas


Name: Megan Herod


Major Advisor: Dr. Jason Martina Committee Members: Dr. Jennifer Jensen, Monica McGarrity



Wednesday, August 3, 2022, 10:00 AM



Invasive species are a global concern and are a significant contributor to anthropogenic global change. As invasive species continue to invade new regions, they impact natural ecosystem function and displace native species. The success and impact of invasive species can be tied to species biology and the attributes of the invaded ecosystem. A two-step experimental approach using a greenhouse experiment and remote sensing methodology was used to develop an understanding of the environmental conditions where Arundo donax, a large-statured invasive wetland species, performs best and how it may colonize a new areas. I predicted that Arundo would exhibit higher values for performance-related traits such as aboveground biomass (AGB), belowground biomass (BGB), net photosynthesis, and total tiller length under high light, high soil moisture, and high nutrient conditions because there would be fewer factors limiting growth for this species. I also predicted that the spread of Arundo would be closely tied to major flood events when the transportation of propagules downstream and the scouring of banks leads to colonization opportunities. Eight of the eleven response variables analyzed, including AGB, BGB, total tiller length, and net photosynthesis showed a significant interaction between soil moisture and shade with plants grown in saturated, high light conditions having the highest values for performance related traits. Nutrients were found to influence biomass allocation patterns, with plants grown with added nitrogen and phosphorous exhibiting higher shoot:root and stem:leaf ratios, however nutrients were not found to significantly influence performance related traits.  Major flood events were shown to influence the rate of spread of Arundo in the studied stretches of the Guadalupe and Medina rivers in Texas. Understanding how invasive species respond to changes in abiotic factors and what influences their ability to colonize new areas is necessary to make predictions about species expansion and prioritize management efforts and can provide necessary information for the development of ecosystem modeling.

 Bio:  Megan Herod is from McKinney Texas. She graduated from the University of North Texas with a B.S in        Ecology for Environmental Science. In her free time Megan enjoys knitting, cooking, and taking care of her house plants. After graduation Megan will continue employment at Copperhead Environmental Consulting.


Thesis Defense

The Family Malvaceae (sensu stricto) in Texas



  Name: Marquise Gates


  Major Advisor: Dr. David E. Lemke


  Committee Members:

Dr. David Lemke - Department of Biology, Texas State University

Dr. Paula Williamson - Department of Biology, Texas State University Dr. Alan Lievens - Department of Biology, Texas Lutheran University

Thursday, July 14th at 10 am on Zoom:

 Passcode: mallow                                                                                                                                                                              

 Abstract: Taxonomic keys are helpful devices that allow instructors, students, botanists, and others to identify  unknown plant specimens. With respect to the flora of Texas, many of the currently available keys for flowering  plant identification have become outdated due to changes in the classification system and may cause confusion f   or users when the keys are based on obscure or highly technical characteristics of the plants. A good example is

provided by the mallow family (Malvaceae) in Texas. The mostly widely-available keys to the family are those presented by Correll and Johnston (1970), however, these keys are largely based on technical characteristics that can be difficult for the inexperienced user to recognize or interpret, making accurate identifications difficult and uncertain.

This thesis focuses on producing new keys and a revised taxonomic treatment for the identification of members of the plant family Malvaceae in Texas. The keys are based on first-hand observation of specimens on deposit in the Biology Department Herbarium at Texas State University (SWT), as well as reviews of online specimen data and images and relevant literature citations. Thirty-one genera and 87 species of Malvaceae are recognized in this treatment as being native or naturalized to Texas. A description of each genus is provided, along with keys and descriptions of the Texas species.

Bio: Marquise Gates is from Dallas, Texas. He graduated from Texas Lutheran University with a B.S. in Environmental Biology in 2019. He enjoys drawing digital art, reading light novels, identifying plants in the lab, and watching anime. He plans on pursuing a career working in the field of plant taxonomy and identification.

Thesis Defense


Name: Israel Arellano

Major Advisor: Dr. Nihal Dharmasiri

Committee Members:

Dr. Sunethra Dharmasiri – Department of Biology, Texas State University

Dr. Hong-Gu Kang – Department of Biology, Texas State University

Tuesday, July 5, 2022, 11:00 am, Supple 376 (Norris Conference Room)

Abstract: Auxin controls many aspects of plant growth and development, primarily by influencing cell division, cell elongation, and cell differentiation. While the simple model of the ubiquitin mediated 26S-proteosome pathway involving SCFTIR1/AFBs explains auxin induced gene expression, recent studies on INDOLE-3-BUTRYIC ACID RESPONSE5 (IBR5) have shown this model is not without nuance. IBR5 encodes a putative dual specificity phosphatase that plays an important, albeit unknown, role in auxin signaling. In many auxin related mutants such as tir1, the degradation of Aux/IAA proteins is slowed down, but in ibr5 mutant backgrounds, Aux/IAA degradation is enhanced. Furthermore, it has been found that IBR5 exhibits holdase activity and interacts with SGT1b, co-chaperone for the foldase HSP90. Recent work on IBR5 indicates that modulation of IBR5 levels in plant affect the abundance of SCF components required for AUX/IAA degradation. To better characterize the role of IBR5 in plant auxin response, Aux/IAA degradation and SCFTIR1 subcellular localization in various mutant backgrounds were analyzed. Results show that IBR5 stabilizes Aux/IAA proteins by reducing SCFTIR1 and Aux/IAA interactions, thus, modulating auxin response. Furthermore, stabilization of Aux/IAAs is antagonistically regulated by SGT1b. IBR5 also modulates levels of CUL1 and ASK1 of the SCFTIR1/AFBs complex and affects nuclear localization of TIR1.  



 Bio: Israel Arellano is from Laredo, TX. He graduated from Texas State University with a B.S. in Biology in 2019. He enjoys learning about Roman history, listening to music, and reading books written by people smarter than he. Upon graduation, he will begin a Plant Pathology PhD program at Texas A&M University.


Thesis Defense



Rachel Seets

Major Advisor: Dr. Kristy Daniel, Department of Biology, Texas State University Committee Members: Dr. Paula Williamson and Dr. Michelle Forsythe

Tuesday, June 21, 2022, 10 am, Zoom 09 Meeting ID: 923 4458 0662                                                       Passcode: Pollinator

Outdoor education is an incredible tool teachers can use to enhance the learning outcomes of their students, however, formal educators face a host of barriers when attempting to implement it. Among these barriers are pressures to meet the demands of state and national standards and standardized assessments, reduced face-to- face interaction between students and teachers, and lack of experience and training in outdoor education design. Outdoor lessons must incorporate the same high-quality science inquiry as seen in traditional, indoor classrooms, but many teachers do not feel confident when designing or implementing these lessons. This brings light to the importance of investigating design methods that will enhance outdoor investigations and ensure that students are developing NGSS science practices when learning outside.

My thesis investigates visual scaffolding techniques as a tool to facilitate science practices in an outdoor education setting through both researcher and practitioner perspectives. The first manuscript is a qualitative research study that investigated the influence of visual scaffolds on student science practices in an outdoor elementary science activity by implementing two versions of an outdoor science investigation with four local classes of fifth graders. Two classes completed a control design with minimal scaffolding techniques and two classes completed a treatment design integrated with scaffolding techniques. Student responses were coded and analyzed for trends in completion and comprehension regarding science practices such as observation, prediction, data collection, data analysis, and constructing explanations. We found evidence suggesting that visual scaffolds are an effective means of engaging students in and modeling science practices outside. Our findings provide simple design tools to teachers who want to bring the benefits of outdoor education to their students and facilitate meaningful science learning. Additionally, findings from this study contribute simple, cost-effective design techniques to the broader context of informal education. The second manuscript included in this thesis is a practitioner’s piece that expands on the application of the visual scaffolding techniques employed in the first manuscript. We provide examples of how we used each visual scaffolding technique in a fifth-grade outdoor investigation about pollinators, and how these techniques can be utilized during outdoor activities to create more meaningful science inquiry.

Bio: Rachel Seets is from Fort Worth, TX. She graduated from the University of North Texas with a B.A. in Biology. She enjoys identifying plants and birds and can often be found hiking out at Purgatory Creek. Upon graduation, she hopes to pursue a career in environmental education.

Dissertation Proposal  


An integrated view of how environment shapes physiological stress markers in a widespread toad (Incilius nebulifer)


Dillon Monroe


Major Advisor: Dr. Caitlin Gabor

Committee Members:

Dr. Andrea Aspbury, Texas State University,

Dr. Veronika Bókony, "Lendület" Evolutionary Ecology Research Group, Plant Protection Institute (NÖVI)

Dr. Susannah French, Utah State University

Dr. Joseph Veech, Texas State University


 June 14, 2022, 10:00AM, IGRM 3203

Abstract: Latitude and urbanization gradients are conglomerates of biotic and abiotic variables that result in interesting trends in vertebrate body size, limb length, and life history. While these trends have been the focus of many studies, the underlying hormonal mechanisms have received much less attention. Glucocorticoids are steroid hormones important to growth and somatic maintenance as well as responding to unpredictable stressors. Studies of geographic variation in glucocorticoid stress response and correlations between baseline glucocorticoid levels and lipid storage, hop performance, and defensive toxin production can help us understand how species might adapt to a changing climate and a changing landscape. I propose to study potential physiological tradeoffs in a widespread toad in Texas (Gulf Coast Toad; Incilius nebulifer) and how those tradeoffs might be mediated by glucocorticoids across a latitudinal and urbanization gradient.

Bio: Dillon was born and raised in Monroe, Utah. He received his B.S. in Biology from Southern Utah University in 2013. After working a few years with various state and federal agencies he decided to continue his formal education at California State University, Northridge. He graduated with his M.Sc. in Biology in 2019. He is Married to Laura Monroe, and they have two kids.

Thesis Defense


Quantification of endocrine disrupting compounds in central Texas rivers and associations with genomic variation in red shiners


Alex Guzman

Major Advisor: Dr. Chris C. Nice Committee Members:

Dr. Caitlin R. Gabor - Department of Biology, Texas State University Dr. David Rodriguez - Department of Biology, Texas State University Dr. James R. Ott - Department of Biology, Texas State University

Dr. Timothy H. Bonner - Department of Biology, Texas State University

Monday, May 30, 11 am, in Supple 116 or on Zoom at Passcode: 500373


Abstract: Over the past decade, chemical pollution has increased in freshwater systems, including increases in endocrine disrupting compounds. One of the most prevalent of these chemical pollutants is 17α-ethinylestradiol (EE2), a synthetic estrogen used for contraceptives. Exposure to EE2 under laboratory conditions has been demonstrated to alter reproduction, development, and behavior of aquatic organisms. Most water quality assessments, however, have detection thresholds that are substantially higher than most observed concentrations of EE2. Furthermore, detection thresholds are higher than biologically relevant concentrations of EE2 as understood from laboratory studies. In this study, I used a sensitive assay to quantify EE2 concentrations in water and red shiner fish, Cyprinella lutrensis, collected from five central Texas rivers. I detected EE2 in all rivers at concentrations that have been shown to cause adverse effects in aquatic organisms. The observed concentrations of EE2 in water and fish suggest that aquatic organisms in central Texas commonly experience non-trivial exposure to EE2. Additionally, given that EE2 can influence reproduction and disrupt development, EE2 exposure could represent a substantial selective pressure for aquatic organisms. I used a Genotype-Environment- Association (GEA) approach to ask whether genomic variation in red shiners was associated with variation in EE2 concentrations. For this, I generated 36,114 single nucleotide polymorphisms (SNPs) for 298 red shiners from 15 localities in five rivers. GEA analysis using Redundancy Analysis included EE2 concentrations in water and fish as predictors of genomic variation as well as other environmental predictors of water quality and patterns of land use in watersheds. Variance partitioning revealed significant proportions of genomic variation explained by my predictors and complex interactions among them. My results indicate that EE2 represents a significant contaminant in central Texas rivers and that there is much more to learn about the impacts on aquatic organisms.


Bio: Alex was born in Austin, Texas and earned his B.S. in Biology from Texas State University in 2020. He joined Dr. Chris Nice's lab immediately after graduation to pursue a Master's in Population and Conservation Biology. After graduation, Alex will begin the Integrative Biology PhD program at the University of California, Berkeley starting Fall 2022.

Dissertation Proposal Defense

Analysis of upland and riparian habitats as stopover sites for migratory songbirds in Central Texas


Name: Dawn Houston

Major Advisor: Dr. Joseph Veech            

Committee Members: Dr. Clay Green, Dr. Sarah Fritts, Dr. Sara Morris (Canisius College)

Dr. Susan Pagano (Rochester Institute of Technology)


Thursday, April 28, 2 PM, Norris Conference Room

Attend in person or by ZOOM:

Passcode: warbler


Abstract:  Migration may be the most perilous and energetically expensive period for migratory birds and it has profound effects on survivorship and subsequent breeding success. High-quality stopover sites, with abundant food resources, allow for rapid refueling of energy stores enabling a songbird to continue on the next portion of its journey. Riparian areas are recognized as important stopover habitats, particularly in the Desert Southwest, whereas upland habitats provide adequate stopover sites in other regions of North America, such as the Midwest. Central Texas lies squarely in the Central Flyway, yet no research to date has investigated stopover habitat in this region. I propose to assess the relative quality of riparian and upland habitats as stopover sites by comparing plasma triglyceride concentrations to indicate refueling performance, plasma uric acid to indicate diet quality, and heterophil to lymphocyte ratios to indicate chronic stress of migratory songbirds. I will also compare fine-scale habitat characteristics, such as the proportion of canopy cover, vegetation height, species composition, and Normalized Difference Vegetation Index (NDVI), between habitat types with regard to migratory songbird abundance. Finally, I will evaluate foraging activity and food abundance (arthropod biomass) to identify which habitat type may be more useful as a resource to migrating songbirds. The goal of my research is to acquire knowledge of stopover habitat ecology in Central Texas that could ultimately inform natural resource agencies and conservation stakeholders of priority habitat for migratory bird conservation. 


Bio: Dawn Romaine Houston was born on Long Island, New York. She earned her Bachelor of Science in Molecular Biology at Florida Institute of Technology. Her interest in avian ecology led her to fieldwork across the country and internationally, but ultimately brought her to Central Texas to earn a Master of Science in Wildlife Ecology at Texas State University in 2008. Since then, she has worked primarily with the endangered Golden-cheeked Warbler and the delisted Black-capped Vireo. She co-founded, 7eco10 LLC, an environmental consultancy aiming to assist landowners with conservation easement establishment and management. Dawn recently returned to Texas State to study for a Ph.D. degree.


Dissertation Defense

Infection dynamics of Ophidiomyces ophiodiicola, the causative agent of ophidiomycosis, in Texas


Name: Stephen Forrest Harding

Major Advisor: Dr. David Rodriguez

Committee Members:

Dr. Camilla Carlos-Shanley, Texas State University Dr. Paul Crump, Texas Parks and Wildlife
Dr. Sarah Fritts, Texas State University
Dr. Michael R.J. Forstner, Texas State University

Tuesday, May 3rd, 2022, 9AM, Supple Science Bldg. Room 116


Abstract: Ophidiomycosis—caused by the fungal pathogen, Ophidiomyces ophiodiicola (Oo)—is an emerging infectious disease (EID) threatening snake populations in North America, Europe, and Asia. In North America, Oo is widespread and has been linked to the decline of two snake populations. In Texas, there have been two confirmed reports of Oo infections; however, considerable knowledge gaps exist for many essential epidemiological factors in the state. For my dissertation research, I address these knowledge gaps by 1) estimating spatiotemporal distributions and host range of Oo in Texas, 2) using historical incidence combined with phylogenetic and population genetic methods to address the origin of Oo in the state, and 3) using field surveys and laboratory experimentation, I assessed the contribution of biotic and abiotic factors to host- pathogen dynamics. I provided an estimate of the contemporary geographic range for Oo in Texas and used multivariate statistics to show seasonal differences in Oo infection prevalence and differences among snakes from different habitat groups. I used historical patterns of Oo occurrence as evidence of the pathogen’s introduction into the state. Using phylogenetic and population genetic analyses, I show strong evidence supporting Oo as a novel pathogen of Texas snakes. I used laboratory infection experimentation to estimate Oo mortality and assess bacterial assemblage differences between infected and non-infected snakes. I detected no differences in bacterial assemblage structure between experimental groups. However, I detected an increased abundance of pathogenic bacterial operational taxonomic units on a host with a moribund infection, suggesting secondary infections synergize with Oo infection to cause mortality. My research narrowed the knowledge gaps for critical epidemiological factors in Texas and identified areas where knowledge gaps still exist, which is vital for future research into the host-pathogen dynamics of Oo in the state.


Bio: Stephen was born and raised in central Texas. He received his B.S. in Aquatic Biology from Texas State University in 2014, and in 2016, he completed his M.S. in the Aquatic Resources program. In 2017, Stephen started his Ph.D. under Dr. David Rodriguez. He is the proud father of Jace and Paige. His passions are fishing, music, and the pursuit of knowledge.


Thesis Defense

Regional Assessment of Inland Fish Mortalities Associated with Winter and Cold-Shock Stresses



Name: Steven G. Lopez

Major Advisor: Dr. Timothy H. Bonner, Department of Biology, Texas State University Committee Members:

Dr. Andrea S. Aspbury, Department of Biology, Texas State University

Dr. Sarah Fritts, Department of Biology, Texas State University


Wednesday, April 13, 2022, 2:30pm, FAB 102 & Zoom

Meeting ID: 930 1318 3544                                                        Password: freeze


Winter is generally regarded as a stressful period for ectothermic animals (i.e., Winter Stress Syndrome), which can be exacerbated by cold shock stress associated with major arctic freezes. Although loosely defined, major arctic freezes consist of abnormally colder air, and therefore abnormally colder water temperatures, for several days (e.g., 2021’s Winter Storm Uri). During major arctic freezes in the 1980s and in 2021, 35 million Texas marine and estuarine fishes were killed attributed to cold shock stress. Interestingly, few studies report the effects of winter stress or cold shock stress on fishes in inland waters. Purpose of this study was to describe patterns in cold weather fish mortalities attributed to winter stress and cold-shock stress within inland waters of Texas between 1969 and 2021 using records contained within Texas Parks and Wildlife Department’s Pollution Response Inventory and Species Mortality (PRISM) database. Among 53 years, reports of cold weather inland fish mortalities occurred in 66% of the years with greatest percentages of the reports occurring during three major arctic freezes in 1981, 1983, and 2021. Majority of the reports were from urban areas (79%) and from lentic environments (56%). Sixteen taxa and 1,000,000 individuals were reported killed during the 53 years.

Numbers of inland fish mortalities were greater in years with major arctic freezes than in years without major arctic freezes, attributed primarily to mortalities of non-native fishes (e.g., Blue Tilapia Oreochromis aureus, Suckermouth Catfish Hypostomus plecostomus). Numbers of native fish mortalities, primarily clupeids and catostomids, were not different between years with and without major arctic freezes. The 43,000 inland fish mortalities reported during the three major arctic freezes are in stark contrast to the 35 million marine and estuarine fish mortalities. Proposed mechanisms to explain cold shock mortalities in coastal environments (e.g., species within the northern extent of their range, lack of access to deeper water) are similar in inland environments, yet inland environments do not have the same level of mortalities. Consequently, the disparity between mortalities in coastal and inland environments are not readily discernable at this time.


Bio: A first generation college student, Steven graduated from Texas A&M University Galveston with a B.S. in Marine Biology and Marine Fisheries in 2020. Steven is from Houston, TX and enjoys spending time in rivers and streams, catching fish and hiking throughout the state. After graduation, he hopes to continue working with inland fish, and gaining a better understanding of aquatic systems.

Thesis Defense


Kyle R. Krebs

Major Advisor: Dr. Jessica Dutton

Committee Members: Dr. Timothy H. Bonner, Dr. Weston H. Nowlin, and Dr. Clay Green


Thursday, April 14, 2022, 12:00 pm, Freeman Aquatic Biology 130 and on Zoom.


Meeting ID: 996 5587 1040  Password: ducks       


Abstract: Mercury (Hg) is global pollutant that is toxic to wildlife at low concentrations. In waterbirds, exposure to Hg has resulted in altered breeding behavior, reduced hatching success, and nest abandonment. There have only been a few studies which assessed Hg concentrations in waterbirds in Texas, despite Texas being one of the greatest Hg emitters in the U.S. and an overwintering location for migratory waterbirds. In this study, tissues (muscle, liver, breast feather, wing feather) from 16 species of waterbirds that overwinter in Texas, including gadwall, green-winged teal, hooded merganser, lesser scaup, northern shoveler, redhead duck, red-breasted merganser, and sandhill crane were collected by TPWD licensed hunters from nine locations throughout the state and analyzed for total mercury (THg) using a direct mercury analyzer. I investigated THg concentrations among species and assigned foraging guilds (granivore, herbivore, omnivore, piscivore) and feeding strategies (dabbler, diver, dabbler/diver, wader) to determine which tissues and species had the greatest THg concentrations. I also investigated whether muscle and liver THg concentrations were above known threshold levels for adverse biological effects in birds and determined which species had muscle or liver Hg concentrations exceeding federal (EPA; 0.3 µg/g) and state (TDSHS; 0.7 µg/g) advisory levels for human consumption. I also investigated the relationship between δ13C and δ15N and muscle THg concentrations, and lastly determined if wing or breast feather THg concentrations could be used to predict muscle and liver THg concentrations. Inter- and intraspecific differences were observed between species and assigned foraging guilds and feeding strategies. The greatest THg concentrations were measured in either wing feather or liver for most investigated species. Overall, THg concentrations were greatest in piscivorous diving waterbirds such as hooded merganser and red-breasted merganser but were also elevated in northern shoveler (omnivorous dabbler) and lesser scaup (omnivorous diver). Seven of the 16 investigated species had THg concentrations in their muscle and/or liver tissue that put them at risk of experiencing adverse biological effects. These same species also exceeded EPA and TDSHS MeHg advisory levels for human consumption. Wing and breast feather THg concentrations did not successfully predict muscle or liver THg concentrations in gadwall or redhead duck. The results from this study indicate that Hg accumulates the most in species that primarily consume fish but can be above concentrations known to cause deleterious biological effects in non-fish-eating species. However, since all species are migratory, future studies need to investigate the extent to which Hg accumulates in tissues while overwintering in Texas.


Bio: Kyle is a first-generation college graduate from San Antonio, TX and earned his B.S in Environmental Science from the University of Texas, San Antonio in 2015. His passion for environmental justice and scientific awareness comes from youth obsessions with Steve Irwin and Bill Nye and he aims to use his M.S in Aquatic Resources to honor their legacies through environmental conservation.

Dissertation Proposal

It’s Not Easy Being Green: The Effects of Agricultural Practices on Stress Physiology and Immune Function in Tadpoles



Name: Amanda Bryant


Major Advisor: Dr. Caitlin Gabor


Committee Members: Dr. Laure Fuess, Texas State University Dr. David Rodriguez, Texas State University

Dr. Jessica Hua, Binghamton University

Dr. Blake Hossack, USGS Northern Rocky Mountain Research Center


Monday, April 11, 2:00pm, in person Supple 257 or join us on Zoom at Passcode: 939721


Abstract: As the human population continues to grow, agricultural practices will need to change to feed the world, but industrial agriculture is a leading cause of habitat loss and population declines in wildlife. Exposure to agricultural pollutants can cause a variety of issues for wildlife including dysregulation of hormonal responses, decreased food availability, decreases in immune function, and increases parasite prevalence. Organic agriculture has shown some promise in minimizing the negative impacts of agriculture in some taxa. However, consequences of organic agriculture on more sensitive taxa are not well understood. Amphibians are the most imperiled vertebrate group on the planet. Amphibians are highly sensitive to agricultural pollution and have been used as bioindicators of ecosystem quality. In amphibians, the glucocorticoid (GC) response modulates behavioral and physiological responses to environmental stressors. It also heavily interacts with the immune response. All immune cells have GC receptors and the increase in GCs during acute stress can be immune stimulatory. However, long term elevation of GCs can be immunosuppressive due to anti-inflammatory action of GCs. This immunosuppression coupled with pollution presence can lead to increases in parasitic infection in amphibians. My goal is to understand the links between the glucocorticoid stress response, immune defense, and parasitic infections in amphibians living in conventional and organic agricultural habitats.

Bio: Amanda was born and raised in Capac, Michigan where she currently conducts part of her PhD research. She received her B.S. from Michigan State University in 2015. She worked with reptiles and amphibians in Michigan, Nevada, Florida, and Guam before starting her PhD in 2019.

Thesis Defense



Michaela L. Livingston

Major Advisor: Dr. Jessica Dutton

Committee Members: Dr. Weston H. Nowlin & Dr. M. Clay Green


Monday, April 11, 2022, 12:30 pm, FAB 102 & Zoom

Meeting ID: 996 6799 7232  Password: flounder                                                                                                                                              ___________________________________________________________________________________

Estuaries are productive coastal environments that are vulnerable to contamination from human activities. Functional Feeding Groups (FFGs) are a biological classification system that break down taxa based on feeding ecology and could be a useful organization system to understand trace element concentrations within a food web. Middle Hempstead Bay, home to both recreationally fished species and vulnerable species, is an estuarine ecosystem within the South Shore Estuary Reserve on Long Island, New York, made up of densely clustered salt marsh islands and connecting water channels. This study investigated the concentration of six essential (Co, Cu, Fe, Mn, Se, Zn) and four nonessential (As, Cd, Hg, Pb) trace elements in sediment and 27 species from Middle Hempstead Bay, including primary producers, insects, mollusks, crustaceans, fishes, birds, and terrapins. Functional feeding groups (e.g., algae, vascular plants, herbivorous insects, invertivore fishes, and piscivorous birds) were composed of a subselection of investigated species and trace element concentrations were compared within and among them. The tissue distribution of trace elements was also examined for four species: saltmarsh cordgrass (Spartina alterniflora), summer flounder (Paralichthys dentatus), common tern (Sterna hirundo), and black skimmer (Rycops niger). Sediment trace element concentrations were greatest for Fe, followed by Mn, Zn, Pb, Cu, As, Co, Se, Cd, and Hg. Except for Co and Se, essential trace elements were at greater concentration in biota than nonessential elements. Algae had significantly greater concentrations of trace elements known to biodiminish in food webs (e.g., Co, Pb), whereas piscivorous feeding groups had greater concentrations of elements known to biomagnify (e.g., Hg). For most trace elements, the concentration was greatest in the roots for saltmarsh cordgrass and liver in summer flounder. Trace element concentrations in common tern tissues were predominantly greatest in liver compared to muscle and feather. Cadmium, Co, and Hg concentrations were similar across black skimmer tissues, and varied across tissue type for the remaining trace elements. This study is the most comprehensive investigation of trace element concentrations within the Middle Hempstead Bay food web. While FFGs proved useful in assessing trace element accumulation, future research is needed to streamline sampling methodology to reduce biological variability that can overshadow trace element concentration patterns among FFGs.

Bio: Michaela was born and raised in San Antonio, TX and now resides in Lockhart with their husband, Paul, and four beloved hounds (Atlas, Bonnie, Cue, Duncan). Michaela earned a B.S. in Biology and B.F.A. in Studio Art from Texas State University, where they solidified their passion for ecotoxicology, communicating science through art, and facilitating science for others. After graduation, they aim to continue their pursuit of aquatic biomonitoring, in hopes of contributing to the conservation of these key ecosystems for the next generation of folks and wildlife.


Thesis Defense

Characterization of a Novel Bacterium that Preferentially Grows in Low Fluid Shear Modeled Microgravity


Calvin Tran

Major Advisor: Dr. Robert JC McLean

Committee Members:

Dr. David Rodriguez, Dr. Camila Carlos-Shanley, Dr. Jiseon Yang (Arizona State University)

Tuesday April 12, 2022, at 2pm CDT

Meeting ID: 940 7443 9314     Passcode :186202


Abstract: Multiple spaceflight and microgravity analog studies have increased our understanding of the biological effects of microgravity. Microgravity or modeled microgravity conditions demonstrate changes in microorganisms including virulence, biofilm formation, gene regulation and expression, and other aspects of physiology. These studies were designed to study microgravity functional impacts on individual organisms, but not as a preferential growth condition. Testing for preferential growth in reduced gravity in some organisms may increase our understanding of the gravitational effect on microorganisms. A novel Exiguobacterium species (A1) was isolated from a laminarly-flowing region of the San Marcos River, which has previously been identified as an organism which may display a preference for growth in a low shear modeled microgravity (LSMMG) environment. Members of the genus Exiguobacterium are Gram-positive bacilli that are often extremophiles.  Exiguobacterium A1 shows a preference for low fluid shear growth when cultured in the lab but is difficult to propagate using conventional culturing methods. Exiguobacterium A1 was grown in Reasoner’s 2A (R2A) and Luria-Bertani (LB) media in both LSMMG and normal gravity (1xG) conditions to identify if there was a nutritional preference in these conditions. In addition, Exiguobacterium A1 has been sequenced, but not yet categorized. Categorization of Exiguobacterium A1 was performed with Biolog Phenotypic Microarrays, Fatty acid analysis and the transmission electron microscopy (TEM) for cellular morphology. Exiguobacterium A1 species name has been proposed as Exiguobacterium astronatus. Exiguobacterium A1 displayed higher cell concentration under 1xG in LB medium after 6 hours and between 6 to 12 hours under 1xG in R2A medium when compared to LSMMG. LSMMG plays a small role initially when growth in R2A media, but overall, Exiguobacterium A1 did not show a preference in growth under LSMMG in either medium.


Bio: Calvin was born in California and has lived in Massachusetts, Florida, and Texas. He graduated in 2016 from Texas A&M University with a Bachelor of Science in Molecular and Cell Biology. He joined Dr. McLean’s lab in the Fall of 2019 when he started his Masters’ at Texas State University. Calvin works as a registered dental assistant since 2013. Calvin will be continuing his education at Tufts University School of Dental Medicine to become a dentist. In his spare time, he enjoys attending music concerts, paddleboarding, playing video games or enjoying the outdoors with his dog, Navi.



Thesis Defense

Implications of Cropping Rate Variability on the Costs of Vigilance

Name: Elizabeth Kurpiers

Major Advisor:

Dr. Floyd Weckerly, Department of Biology, Texas State University

Committee Members: Dr. Andrea Aspbury, Department of Biology, Texas State University

Dr. Clay Green, Department of Biology, Texas State University

Thursday March 24th, 1:00 PM

Please attend in-person in W.E. (Henry) Norris, Jr. Conference Room (Supple 376) or via Zoom:

Abstract: Large grazing ungulates must forage for much of their active time to meet the energy demands of their massive bodies because they depend on nutrient-poor grasses and forbs. As such, maximizing efficiency of foraging bouts is selectively advantageous. Vigilance is a social and antipredator behavior that can result in reduced predation risk; however, vigilance directly competes with foraging and imposes an inherent foraging efficiency cost. As more time is allocated to vigilance, less time is available to forage. Using 199 focal observations of Roosevelt elk (Cervus elaphus roosevelti) collected in the Redwood National and State Parks of Northern California, I explored if the variability in elk cropping rate results in increased short-term forage intake and subsequently compensate for foraging time lost to vigilance. Notably, compensation via increased cropping rate is likely only feasible when food searching time is minimal and bite sizes are small, conditions that were satisfied in our study area. I developed and compared two novel models that describe possible mechanisms in which cropping rate compensation could occur. The Strategic Compensation Model illustrates a scenario where cropping rate compensation occurs due to a deliberate decision by foraging elk to increase their cropping rate. In contrast, the Incidental Cropping Variability Model describes a situation where cropping rate variability is not strategic, but rather occurs due to the influence of social and environmental factors on cropping rate. I compared the proportion of time elk spent vigilant to their cropping rate (bites . observation length-1). Four linear mixed-effect model were developed and compared using Bayesian model selection analysis. Three of the four models were identified as competing models, and each of the competing models contained the predictors: the proportion of the foraging bout spent vigilant, proportion of the foraging bout spent within one body length of a conspecific, time of day, and length of the focal observation. The influence of these predictors on cropping rate demonstrates that external factors influence cropping rate and supports the idea that cropping rate variability is incidental, likely occurs sporadically, and can compensate for vigilance in certain circumstances.

Bio: Liz was born and raised in Maple Grove, Minnesota. In 2017, She earned her B.A. in Biology and Hispanic Studies from the College of Saint Benedict, a small, liberal arts college in central Minnesota. After graduating, Liz worked at a preclinical research lab as an Associate Pharmacologist testing pain mitigation methods and drugs. Liz has a love of the outdoors, is in training to become a Master Naturalist, and has worked on field projects including sage-grouse monitoring, tree swallow surveys, and Sally-light foot crab behavioral studies. Liz joined the lab of Dr. Weckerly in 2020 and has since been studying Roosevelt elk and white-tailed deer foraging behavior.

Thesis Defense

Factors Influencing Scaling Relationships of Body and Antler Mass in White-tailed Deer (Odocoileus virginianus)

Willis Sontheimer

Major Advisor: Dr. Floyd Weckerly

Committee Members: Dr. Ivan Castro-Arellano, Texas State University

Dr. Clay Green, Texas State University

Friday, 25 March 2022, 3:00 PM

Attend in-person in IGRM 3104 or on Zoom

Passcode: 692363

Antlers are a costly trait that require skeletal reserves to grow to a large size. Thus, insight into variation in antler size requires understanding the connection between antler and body size, which can be summarized through ontogenetic and static scaling relationships. Both types of scaling relationships are needed to examine the influence of factors besides body mass on antler growth at different ages and whether the influence of these factors diminish with age. Diet variability and maternal effects might decline with age as individuals attempt to make up for size deficits through compensatory growth. I sought insight into the influences of diet and maternal attributes of dam age at birth and litter size on body-antler size relationships throughout ontogeny and at discrete ages. I also examined whether diet and maternal effects diminished with male age. Data on age, maternal characteristics, body mass, and antler mass was gathered from 168 captive, pen-raised white-tailed deer (Odocoileus virginianus) that consumed either a low energy (1.77 kcal/gm) or standard energy diet (2.65 kcal/gm) from the time they were weaned until they died by age 5.5 years of age. Both types of scaling relationships were estimated with linear mixed effects models to account for repeated measurements of males, dams, and sires. Diet affected ontogenetic scaling relationships. Males consuming the low energy diet had faster antler growth when young than old; compared to males consuming the standard energy diet. A Bayesian Information Criterion model selection analysis indicated that diet and litter size (singleton or multiple births), but not dam age at birth influenced static scaling relationships. Static scalar coefficients up to 3.5 years of age were positively allometric, but isometric in 4.5- and 5.5-year-old-males. Furthermore, diet and litter type influenced both intercepts and slopes in only the youngest males (1.5-years) lending support to the idea that diet and maternal effects diminish with age. Body size – antler size relationships are complex. Diet and litter type had greater effect at younger ages during rapid growth than at older ages. Young males that are small because of maternal effects might still be able to acquire large body and antler sizes at older ages when diets provide adequate nutrition.

Biography: Willis was born and raised in Norman, Oklahoma. He graduated from the University of Oklahoma with a B.S. in Biology in 2014. He works as a biologist for the Texas National Guard.


Announcements of past thesis and dissertation defenses can be found in the documents below. These announcements include student name, major adviser, committee members, and date, as well as an abstract of thesis or dissertation.

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