Theses and Dissertations from UMD
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Item TREE GENETICS AND GREENSPACE MANAGEMENT INTENSITY INFLUENCE URBAN TREE INSECT COMMUNITIES, DAMAGE, AND FOLIAR TRAITS(2024) Perry, Eva Emma; Burghardt, Karin T; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Trees are essential to well-functioning urban systems, providing services that benefit humans and wildlife. For example, arthropods that use trees in cities perform key roles in the urban food web as both prey and predators, but they can also be vulnerable to environmental stressors associated with cities. Previous work documents broad patterns in arthropod communities associated with management practice gradients in urban areas. How these patterns relate to changes in tree genetic background across management types remains a largely unexplored topic. To disentangle the genetic and management associated effects on arboreal insect abundance, communities, and foliar damage, I repeatedly sampled trees of known genetic relatedness for two commonly planted tree species: Acer rubrum (n = 65), and its non-native congener Acer platanoides (n = 71), in June and August of 2023 and 2024. I systematically selected about 3 individual trees growing in four human management intensity categories (street trees, parks and residential yards, urban forest patches, or rural forests) for each of 5 genetic lineages per tree species. I used vacuum sampling to collect mobile arthropods from the lower canopy of each focal tree in June and August of 2023 and 2024, and identified samples to order. I also assessed insect and systemic foliar damage, gall abundance, and select physiological traits in August 2024. I found the general trend of increasing total arthropod abundance with increasing management intensity. However, management effects differed across genetic background with almost ubiquitous interactions between management type and genetic lineage. The most dominant group of insects found on study trees belonged to the order Hemiptera. This group of primarily herbivorous piercing/sucking insects were the primary drivers of these overarching abundance patterns. Spiders, which were the most abundant primarily predatory arthropod order, exhibited the opposite pattern, increasing in overall abundance in the later season, decreasing with increasing management intensity, and generally not responding to tree genetic lineage. In 2024, increasing management intensity negatively affected cumulative insect herbivore damage and gall abundance, and did not vary by genetic lineage. Gall formers were found only on native Acer rubrum, with no galls sampled from the non-native A. platanoides. In contrast, systemic foliar damage did not change with management, and only varied by tree genetic lineage for Acer platanoides. Foliar photosynthetic traits’ variance by management intensity or tree genetic lineage was species dependent; A. rubrum traits varied by tree genetic lineage, while A. platanoides traits varied by management intensity. Overall, my results suggest that tree genetic background plays an important role in mediating management effects on insect populations, particularly for piercing-sucking herbivorous species, but genetic background’s effect on other metrics such as foliar damage and traits may be species-specific. Further studies should be sure to consider the structure of genetic populations when describing patterns of insect use. Results of this thesis will serve to inform best practices for urban tree management and pest mitigation, as cities work to maintain and increase urban canopy cover.Item Using CRISPR/Cas9 to functionally dissect Blimp1, a newly identified pair-rule gene in the hemipteran Oncopeltus fasciatus(2024) Reding, Katie; Pick, Leslie; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Genetic screens in the fruit fly Drosophila melanogaster identified a class of mutants displaying half as many segments as seen in wild type fly larvae (Nüsslein-Volhard and Wieschaus 1980). Careful examination of the larval cuticle revealed that one out of every two segments were deleted across the anterior-posterior (AP) axis, an unexpected phenotype suggesting that segmentation in Drosophila follows a ‘pair rule’. Thanks in part to the many genetic tools available for this model species, we now have a clear picture of how the AP axis of the Drosophila embryo is polarized and subsequently divided into distinct segments, and how the pair-rule genes (PRGs) define alternate segments during this process. Since all insects share a similar body plan, it is reasonable to expect that the processes regulating establishment of this body plan would be conserved. However, studies of the Drosophila segmentation gene orthologs in non-model insects suggest that this is not always the case. While the use of model organisms enables an unmatched depth of understanding of the mechanisms underlying development, it comes at the expense of understanding the diversity of these mechanisms across taxa. The milkweed bug Oncopeltus fasciatus (Ofas) (Hemiptera) is a particularly useful insect to study in this regard, as none of the orthologs of the Drosophila PRGs have clear PR-function in this species (Liu and Kaufman 2005b; Auman and Chipman 2018; Reding et al. 2019), while the gene E75A, which has no role in segmentation in Drosophila, is expressed in a PR pattern and its knockdown yields PR segmentation defects (Erezyilmaz et al. 2009). These results suggested that PR-regulation of segmentation in Oncopeltus might require a different set of factors than those discovered in Drosophila. To identify other non-canonical PRGs in this species, I conducted an expression pattern-based screen of transcription factor-encoding genes that are co-expressed with E75A during embryogenesis, and have identified the gene Blimp1 as an Oncopeltus PRG. Like the Drosophila PR mutants, Ofas-Blimp1 mutants display loss of alternate segments across the AP axis. No roles of Blimp1 in insect segmentation had been identified prior to this finding. This result suggests that while insect segmentation may be constrained to follow a pair rule, the genes responsible for regulating PR-segmentation are evolutionarily labile. Further, a major barrier to studying gene function in non-models is the lack of genetic tools such as visible markers and established methods for gene editing. Here I will describe deployment of CRISPR/Cas9 technology in Oncopeltus for targeted mutagenesis. While mutation of the ABC transporter-encoding gene white proved to be recessive lethal, I was able to generate a viable visible marker line by disrupting the X-linked gene Ofas-vermilion (v). Of-v is required for production of dark brown eye pigments, thus Ofas-v mutants have bright red eyes, easily discernible from the black eyes of wild type bugs. I show that a co-CRISPR approach using Of-v as a marker of germline mutation is a helpful strategy to identify mutations of interest at unlinked loci, enabling many future genetic manipulations in this species.Item HEMIPTERAN INSECTS AS MODELS FOR UNDERSTANDING SEGMENTATION(2018) Chen, Mengyao; Pick, Leslie; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although segmentation is highly conserved in arthropods, diverse mechanisms underlie segmentation. Pair-rule genes (PRGs) are a group of genes controlling segmentation in Drosophila melanogaster, a holometabolous insect. While Drosophila are long-germ insects, most insects add segments sequentially. Studying the role of PRGs in sequentially-segmenting species will provide a deeper understanding in terms of developmental biology. Here, I studied two such insects: Halyomorpha halys and Oncopeltus fasciatus, hemimetabolous insects in a sister order to Holometabola. I annotated segmentation genes in the Halyomorpha genome and tested its response to RNA interference which I showed to be effective in this species for the first time. I further showed that three orthologs of Drosophila PRGs are present in the Oncopeltus genome and are expressed during stages at which segments are specified. Surprisingly, only one of these orthologs is expressed in a PR-pattern, indicating that PRG expression and function have changed during insect evolution.