Biological Sciences Doctoral Work

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Alignment of Genetic Variation, Plasticity, and Selection, and the Effects of Cost of Plasticity
(North Dakota State University, 2021) Berdal, Monica Anderson
Phenotypic expression depends on both the underlying genetics and the environment the phenotype is expressed in, i.e., plasticity. Adaptive theory predicts that selection should align with the dimensions of most genetic variation and plasticity because this will increase the evolutionary rate of a population, meaning that a population would reach its fitness optimum faster than if they were misaligned. Alignment with selection is only predicted if there is directional selection, and not under stabilizing selection. In addition, only adaptive plasticity is predicted to align with both selection and genetic variation, with the proportion of the plastic variation consisting of adaptive plasticity determining how well aligned plasticity should be. In the first chapter of this dissertation, I outline the evolutionary consequences of the relationship between selection, genetic variation, and plasticity, as well as what the predictions are for their alignments and how to estimate them. In my second chapter I empirically test the alignment between selection, among- and within-individual variation (used as proxies for genetic variation and plasticity respectively) for three behaviors in a wild population of deer mice (Peromyscus maniculatus). I found that selection, among- and within-individual variation were all misaligned, and that there was very little variation in all three behaviors. This could indicate that the behaviors have already reached their fitness optimum due to previous selection pressure. Consequently, this population might not be able to adapt to environmental change. In my last chapter I investigate the cost of plasticity in response to a predatory cue on reproductive outputs in isogenic lines of the banded cricket (Gryllodes sigillatus). Plasticity is assumed to have associated costs which would affect its alignment with selection and genetic variation. I found no evidence for cost of plasticity in G. sigillatus, and in addition there was no genetic variation in plasticity among the lines. Again, previous selection might drive the population’s mean plasticity to its fitness optimum, reducing the variation and the costs of plasticity, making it harder to detect.
Developmental Effects on Immunity: Hormonal and Proteinase Control
(North Dakota State University, 2016) Booth, Kimberly Katie
Insects are ubiquitous, diverse, and able to combat infections despite their lack of adaptive immunity. Insects have a robust innate immune system that is divided into two branches, cell-mediated and humoral. Activation of cell-mediated immune responses results in phagocytosis, nodule formation, and encapsulation by the insect’s immune cells, hemocytes. Activation of humoral immunity results in the production of anti-microbial peptides (AMPs) and phenoloxidase (PO). Insect immune responses can be plastic with development. However, research on how and why insect immunity changes with age as insects develop within a larval developmental stage (instar) is limited and contradictory. In my dissertation research, I answer two main questions: 1) how do immune responses vary within an instar and 2) what drives changes in immunity within an instar? My dissertation research showed that humoral immune responses are more robust at the beginning of the 5th and final instar in Manduca sexta (tobacco hornworm) compared to responses from animals later within that instar. Many changes occur within an instar that could affect immunity. For example, I found that protein expression of matrix metalloproteinase (MMP) in immune tissues of M. sexta decreases throughout the 5th instar. Though MMPs are involved in immune responses in other insects, MMP was not found to be immunostimulatory in M. sexta. Another important factor that changes within an instar is the level of juvenile hormone (JH). JH, a developmental hormone that prevents early molting, peaks early and decreases within an instar until molting. I determined that JH is necessary to survive an infection, control bacterial growth in hemolymph (insect blood), and mount an AMP activity immune response. My dissertation research has established that there is a development-immunity link, and that the naturally fluctuating levels of JH may mediate the effect of development on immunity.
Ecophysiological Implications of Spring Conditions on the Alfalfa Leafcutting Bee, Megachile rotundata
(North Dakota State University, 2017) Bennett, Meghan Marie
Spring conditions stimulate development of many plants and animals after a period of winter dormancy. Climate change is predicted to cause earlier spring thaws, increasing temperature variability, and more frequent cold snaps. These conditions cause two problems for organisms. First, environmental cues may mislead organisms developing under these scenarios if temperature and photoperiod cues give conflicting information. Second, organisms outside of their overwintering stages can be less tolerant of cold exposure and may be at risk of injury or death. Little is known about the consequences of these conditions on bee species. Therefore, I examined these scenarios in a solitary bee species, Megachile rotundata. I hypothesized they would be sensitive to temperature changes to regulate spring emergence because of their cavity nesting life history where photoperiod cues likely buffered. I found light is buffered by the brood cell by approximately 80% and emergence can be synchronized by photoperiod. Furthermore, I demonstrated that M. rotundata may be more sensitive to temperature cues compared to photoperiod cues in regulating emergence. To understand how spring cold snaps during development affect adult bees, I comprehensively assayed M. rotundata cold tolerance. I discovered that cold exposure during development resulted in numerous sub-lethal effects in adult bees such as a decrease in flight performance and longevity. Furthermore, developmental cold stress affected adult thermal performance, such as chill coma recovery. Cold tolerance varies across development and the post-diapause quiescent stage was more tolerant to cold than pupal or emergence ready stages. Temperature fluctuations of spring may affect the timing of emergence but also the health of adult bees if they experienced a cold snap during development.
Effects of Phylogenetic Tree Style on Student Comprehension
(North Dakota State University, 2017) Dees, Jonathan Andrew
Phylogenetic trees are powerful tools of evolutionary biology that have become prominent across the life sciences. Consequently, learning to interpret and reason from phylogenetic trees is now an essential component of biology education. However, students often struggle to understand these diagrams, even after explicit instruction. One factor that has been observed to affect student understanding of phylogenetic trees is style (i.e., diagonal or bracket). The goal of this dissertation research was to systematically explore effects of style on student interpretations and construction of phylogenetic trees in the context of an introductory biology course. Before instruction, students were significantly more accurate with bracket phylogenetic trees for a variety of interpretation and construction tasks. Explicit instruction that balanced the use of diagonal and bracket phylogenetic trees mitigated some, but not all, style effects. After instruction, students were significantly more accurate for interpretation tasks involving taxa relatedness and construction exercises when using the bracket style. Based on this dissertation research and prior studies on style effects, I advocate for introductory biology instructors to use only the bracket style. Future research should examine causes of style effects and variables other than style to inform the development of research-based instruction that best supports student understanding of phylogenetic trees.
Evidence of Climate Niche Creation in the Northern Great Plains: The History of Invasion, Population Genetics, Competitive Effect, and Long-Term Trends of Invasive Poa Pratensis L.
(North Dakota State University, 2016) Dennhardt, Lauren Alexsandra
Understanding the mechanisms of invasion is critical in order to control an invasive species. Poa pratensis L. (Kentucky bluegrass) is an invasive species that has been present in the northern Great Plains (NGP) for over 100 years, but has become a dominant species in the mixed grass region recently. My dissertation seeks to answer one critical question—why has P. pratensis become such a successful invasive species in the NGP? I first asked if the invasion was caused by adaptation and/or propagule pressure. I screened the genetic fingerprint of invasive P. pratensis in the NGP along with measuring the genomic content of wild plants and compared them to common cultivars. I found virtually no overlap between lawn cultivars and invasive P. pratensis populations. This was further supported by a narrow range of genomic content in wild individuals compared to the lawn cultivars. I also found no evidence of geographical patterning which is consistent with the hypothesis that local adaptation is not pervasive in P. pratensis. I then asked whether P. pratensis was a strong competitor compared to dominant plant species native to the tallgrass prairie. I studied competitive effect between Poa pratensis, Nassella viridula, Pascopyrum smithii, and Bouteloua gracilis through a species-pair competition experiment. Based on the relative interaction indices, P. smithii and P. pratensis were competitive against B. gracilis, and P. smithii was competitive against N. viridula. Additionally, P. pratensis was facilitated by all three species in the experiment. This study indicates that P. pratensis may be somewhat competitive. Finally, I asked whether the increase in the frequency of P. pratensis in the NGP may be attributed to environmental factors. In order to understand long-term correlations between P. pratensis invasion and environmental variables, I resampled plots that were previously sampled for species composition in 1978, 1979, and 1999. I found that P. pratensis levels did increase across plots and was corrrelated with higher levels of precipitation. My research indicates that increased precipitation in the NGP as a result of climate change is correlated with P. pratensis invasion in the NGP.
The Evolution and Development of a Novel Trait in Sepsidae
(North Dakota State University, 2016) Melicher, Dacotah
Evolutionary novelty, the appearance of new traits with no existing homology, is central to the adaptive radiation of new species. Novel traits inform our understanding of development and how developmental mechanisms can generate novelties. Sepsid flies (Diptera: Sepsidae) have a sexually dimorphic, jointed appendage used for courtship and mating. The appendage develops from the fourth abdominal histoblast nest rather than an imaginal disc. Histoblast nests in other species produce the adult epidermis and lack three-dimensional organization. The sepsid system is an opportunity to investigate the evolutionary history of a novel trait and the developmental mechanisms that pattern epidermal tissue into a complex structure. The appendage has a complex history of gain, loss, and recovery over evolutionary time. Appendage morphology is highly variable between species and does not correlate to body size. I collected larval epidermal tissue from 16 species across Sepsidae and one outgroup to trace the evolutionary history of gain, secondary loss, and recovery. I characterized histoblast nests in all segments and sexes, determining the nest size, number, and size of cells. The appendage-producing nest is sexually dimorphic in species after primary gain. Loss of the appendage shows a return to ancestral state while regain shows an increase in nest size in both sexes. The loss of sex dimorphism may indicate that mechanisms involved in specification may be active in females while genes involved in patterning are not activated during pupation. I assembled and annotated a reference transcriptome for the sepsid Themira biloba at using a custom bioinformatic pipeline that uses a merged assembly approach to maximize quality. This pipeline demonstrated an improvement over other methodologies using multiple published metrics for determining quality and completion. This pipeline also demonstrates how cloud computing architecture can complete bioinformatic tasks quickly and at low cost. I used the T. biloba transcriptome to identify differentially expressed genes involved in appendage patterning during pupation. I sequenced the appendage producing fourth male larval segment and the third male and fourth female segments. Many of the differentially expressed transcripts are involved in cell signaling, epidermal growth, and transcripts involved morphological development in other species.
Examination of Age at Death Methods and the Effects on Estimation Accuracy when Applied to Computed Tomography Scans and Virtual Models of Mummies
(North Dakota State University, 2015) Schanandore, James
Three-dimensional (3D) medical imaging provides a method to non-invasively examine the sub-surface structures of a mummified body, particularly the skeleton. The unique nature of both natural and anthropogenic mummification processes causes inconsistencies for estimating accurate age at death for a particular mummy or group of mummies. These inaccuracies are compounded when age at death methods are used in relation to 3D virtual models. There is a need for the examination of methods being used in mummy case studies and how they are being applied to the 3D virtual models. My research encompassed three studies that addressed the relationship of and the variability when estimating age at death of mummies using radiological imaging. In one study, 146 published case studies were examined for which methods were used to estimate age at death. This study found that articles often provided an assessment of age, but many failed to specify the methods used to calculate the estimated age, and if specified methods were limited to certain areas of the body. In a second study, a cohort of age at death methods was applied to a sample of 17 adult mummies and it was determined that some methods do not transpose well and consequently provided inaccurate age at death estimations when applied to 3D virtual models. Modifications to traditional osteological approaches for age estimation were sometimes necessary due to the presence of soft tissue and post-mortem changes to the body. This study proposes that more methods are needed that utilize the tools available for radiological images in order to limit the variability of transposing a traditional age at death method to virtual 3D models. In the third study, the rim height of the auricular surface was measured using computed tomography scans of 97 living or recently deceased individuals’. These measurements targeted areas around the edge of the surface, for example the height of the apex above the surface. The rim height above the surface produced models that can accurately predict age at death.
Interaction and Innovation: The Impacts of Social Factors and Classroom Type on University Biology Instructor Classroom Assessment Decisions
(North Dakota State University, 2020) McConnell, Melody Dawn
Efforts to improve university science education continue to emphasize the importance of active learning, including frequent formative assessment and timely feedback that helps students reach desired learning outcomes. Yet, nationwide, many instructors continue to use primarily lecture-based teaching methods, with limited use of formative assessment and feedback. Factors that affect instructor adoption and implementation of new teaching techniques include departmental norms, peer interaction, and classroom environment. In this work, a model of the impacts of departmental teaching and social norms and peer interactions on instructor innovation decision is presented. This model is then used to explore 1) instructor teaching-related interactions within a single biology department, assessing the conditions for innovation diffusion, and 2) instructor perceptions of norms and interactions in that department and their impact on decision-making. Finally, introductory biology instructors’ use of assessment and feedback techniques were characterized in a lecture hall and an active learning classroom to see how innovation adoption translates to specific assessment practice and investigate the impact of the active learning classroom. Results indicate that perceptions and practices vary widely, but that both peer interactions and active learning classrooms may have a positive impact on teaching innovation adoption and practices in a university biology department. In addition, the pattern of interactions within this department allows instructors of varying assessment experience to interact, making it potentially conducive to the spread of teaching ideas. The model and results presented here will assist in understanding the factors involved in instructor decision-making and can be leveraged to help promote the use of formative assessment and other evidence-based teaching practices.
Peripheral Hormone Interactions with the Growth Hormone-Insulin-Like Growth Factor (GH-IGF) System in Rainbow Trout
(North Dakota State University, 2019) Dickey, Lindsey Ann
The growth of vertebrates is primarily regulated by the growth hormone-insulin-like growth factor (GH-IGF) system, but not in isolation. The central question of this dissertation was how do other hormones peripheral to the GH-IGF system interact with the system, including feedbacks by GH and IGF themselves on various tissues in rainbow trout (Oncorhynchus mykiss)? The representative hormones selected were thyroxine, cortisol, and the sex steroids testosterone and estrogen, along with GH and IGF. These hormones were chosen because they are known to affect overall growth and development during specific life events, but exactly what target genes and what mechanisms are involved are only at the early stages of being delineated in fish. Liver and gill tissues were selected as representative tissues to assess the in vitro effects on growth-related genes of the GH-IGF system. A total of more than thirty experiments were conducted, including time- and concentration-response, inhibitory studies, hormone combination studies, and radio-receptor binding assays. Hormones were applied to whole tissue cultures and real-time quantitative-PCR was used to measure hormonal effects on GHR, IGF, and IGFR1 genes. Microsomal preparations were treated with selected hormones and radio-labeled GH or IGF. A gamma counter was used to measure receptor-ligand activity. GH and IGF were found to possess autocrine and/or paracrine actions in self-regulating target growth genes. Thyroxine had no direct effects on targeted growth genes but may interact with other molecules or hormones to elicit its effects on growth and development. Cortisol directly influenced target growth genes in a tissue-specific and isoform-specific manner. Finally, sex steroids differentially regulated the growth genes: estradiol inhibited growth genes while testosterone directly stimulated growth genes. These findings contribute to understanding how hormones peripheral to the GH-IGF system interact with the growth system.
Physiological Mechanisms Underpinning Growth and Aging in Wild Birds
(North Dakota State University, 2019) Sirman, Aubrey Erin
Life-history trade-offs have been well-documented within the literature through correlational and experimental studies. However, the physiological mechanisms underlying these trade-offs are less understood. Currently, there is great interest in shared mechanisms, specifically endocrine mechanisms, that might underlie the variation in life-history traits. Insulin-like growth factor-1 (IGF-1) may be one shared mechanism that is particularly important. IGF-1 is a metabolic hormone that is part of a highly conserved insulin-signaling pathway known to influence multiple life-history traits including growth and longevity across taxa, however, little is known about these trade-offs outside of laboratory populations. This dissertation focuses on the role of IGF-1 as a hormonal mechanism underlying the life-history trade-off between growth and aging in wild birds. While the causes of aging are not fully understood, telomere dynamics (length and change in length) are a potentially important mechanism underlying lifespan. To investigate the role of IGF-1 as a hormonal mechanism underlying the life-history trade-off between growth and aging in Franklin’s gulls (Leucophaeus pipixcan) and house sparrows (Passer domesticus). In Franklin’s gulls, dietary restriction reduced growth rate and IGF-1 levels but did not impact telomere dynamics. However, there was a significant negative correlation between IGF-1 levels and telomere length at the end of the post-natal growth period. In house sparrows, we found that nestling growth rates varied with respect to year, but IGF-1 levels did not. Telomere dynamics were not related to growth rates or IGF-1 levels, suggesting that during post-natal growth nestlings may be able to mitigate or even delay costs to later life stages. Finally, when exogenous IGF-1 was administered to house sparrow nestlings during the post-natal growth period, nestling growth was impacted but only in some years. Exogenous IGF-1 increased growth and final mass in 2016 and final mass in 2018. There was a trend suggesting experimental birds had shorter telomeres in 2016. Similarly, in 2018, experimental birds had significantly shorter telomeres than control birds. These effects were not observed in 2017, suggesting that trade-offs between growth an aging might only be visible under certain environmental conditions, which may vary with respect to year.
Using a Cross-Cutting Theoretical Framework to Explore Difficulties Learning Human Anatomy and Physiology
(North Dakota State University, 2020) Slominski, Tara Nicole
Across the United States, Human Anatomy and Physiology (HA&P) courses typically have some of the highest withdrawal and failure rates on college campuses. These high enrollment course typically serve as gate-keepers for those individuals with aspirations of entering the medical field. In light of the growing national shortage of healthcare professionals, there is a pressing need to improve the state of HA&P education at a national scale. The goal of this dissertation is to understand why undergraduate students struggle to succeed in HA&P courses. I leveraged multiple frameworks from biology education research, physics education research, and cognitive psychology to understand the source of student difficulty in HA&P. I used a mixed-methods approach to unpack how students reason about the complex phenomena covered in HA&P classes. The data presented here suggest student difficulties in HA&P are not the product of a culmination of individual conceptual difficulties. Rather, this work suggests students have difficulty reasoning with the many complex systems that are at the heart of HA&P curriculum. Students appear to frame these complex systems in a manner that activates reasoning strategies that are often in conflict with course goals. The findings from this work advocate for a dynamic view of student cognition that recognizes the implications of context features on student reasoning of complex systems.

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