Entomology
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Item INVESTIGATING PAIR-RULE GENE ORTHOLOGS IN AN INTERMEDIATE GERM BEETLE, DERMESTES MACULATUS(2017) Xiang, Jie; Pick, Leslie; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Insects share a body plan based on repeating segments. Segmentation has been well characterized in Drosophila melanogaster, in which segments are established by a genetic hierarchy including gap, pair-rule and segment polarity genes. Pair-rule genes (PRGs) are a key class of segmentation genes as they are the first cohort of genes expressed in a periodic pattern. Segments are established simultaneously in Drosophila in early embryos, while most other insects add segments sequentially as the embryo elongates. Our goal is to understand molecular mechanisms controlling segment formation and to determine the extent of their conservation during evolution. Here, we established the hide beetle Dermestes maculatus, an intermediate germ developer, as a new model system for studying segmentation patterning. We first established a lab colony and studied early embryogenesis in Dermestes. All nine PRG orthologs were isolated using degenerate PCR and RACE, and their expression patterns were examined with in situ hybridization. Except for opa, all Dermestes PRG orthologs are expressed in PR-like striped patterns. Gene functions were tested using RNA interference (RNAi). We examined both hatched and unhatched larvae to uncover defects with different severities. Both Dmac-prd and -slp knockdown resulted in typical PR defects, suggesting that they are “core” PR genes. Dmac-eve, -run and -odd have dual roles in germ band elongation and in PR segmentation, as severe knockdown caused anterior-only, asegmental embryos while moderate knockdown resulted in PR-like defects. Elongated but asegmental germ bands resulted from Dmac-prd and -slp double knockdown, suggesting decoupling of germ band elongation and PR segmentation. Extensive cell death prefigured the cuticle patterns after knockdowns, seen long ago for Drosophila PR phenotypes, although disrupted cell mitosis was also observed after Dmac-eve knockdown. We propose that PRGs have retained basic roles in PR segmentation during the transition from short-to-long germ development and share evolutionary conserved functions in promoting cell viability. Finally, I also present detailed protocols on Dermestes lab rearing, embryo collection and fixation, in situ hybridization and RNAi. The technical information described here will provide useful information for other genetic studies in this new model system.Item Taxonomic revision, phylogenomic analyses, and natural history of the fungus-farming ant genus Sericomyrmex (Hymenoptera: Formicidae)(2016) Jesovnik, Ana; Mitter, Charles; Schultz, Ted R; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fungus-farming ("attine") ants, a New World clade of nearly 300 species in 16 genera, are model systems for studies of symbiosis, coevolution, and advanced eusociality. All attine ants cultivate fungal symbionts for food. "Lower" attine ants cultivate facultatively symbiotic fungi, but in "higher" attine ants both ants and fungi are obligate, highly coevolved symbionts. Sericomyrmex is a poorly studied higher-attine genus known for its problematic taxonomy. This work represents the first comprehensive study of Sericomyrmex species and their fungal cultivars. For Chapter One I sequenced, assembled, and analyzed transcriptomes of three species of Sericomyrmex and a lower-attine-ant species, Apterostigma megacephala. I characterize the transcriptomes, conduct phylogenetic analyses, and search for genes of interest, most importantly arginine biosynthesis pathway genes, the absence of which in A. megacephala strongly suggests that attine ants became dependent on their fungi early in their evolution. In Chapter Two I address the phylogenomics of Sericomyrmex, sequencing ~990 ultra-conserved-element loci for 88 Sericomyrmex samples. Maximum-likelihood and species-tree phylogenetic methods recover nearly identical topologies across data sets, identifying nine species-level lineages. Divergence-dating analyses indicate that Sericomyrmex is the product of a recent, rapid radiation, with a crown-group age estimate of 4.3 million years. I sequence two nuclear ribosomal regions for 32 Sericomyrmex fungi. The fungal phylogeny indicates that Sericomyrmex cultivars are generalized higher-attine cultivars, which, rather than forming a separate clade, are interspersed with Trachymyrmex-associated fungi, indicating cultivar sharing and horizontal transfer between those genera. In Chapter Three, guided by my phylogenomic results, I study the morphology of Sericomyrmex workers, males, queens, and larvae and conduct a comprehensive taxonomic revision, including a key to the worker caste and species distribution maps. Sericomyrmex comprises 11 species, including three new species. The number of recognized species is lower than the previously recognized 19 species and three subspecies. In Chapter Four I review the literature of and report newly acquired data on the natural history of Sericomyrmex, with a focus on nesting biology, presenting data for 19 nests of seven Sericomyrmex species.Item The role of host-plant hybridization in host-associated population divergence in Phytomyza glabricola (Diptera: Agromyzidae)(2012) Hebert, Julie Byrd; Hawthorne, David J.; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Phytomyza glabricola (Diptera: Agromyzidae) is a leaf-mining fly native to the eastern United States that mines two sympatric native holly species, Ilex coriacea and I. glabra. Recent work revealed significant genetic divergence between host-associated populations of flies in North and South Carolina, suggesting the populations are host forms and recent work in Ilex phylogenetics hint the two holly hosts may hybridize. In this work, I investigated potential ecological speciation in P. glabricola, hybridization in its host plants, and how the hybridization among host plants may affect gene flow between host forms of the flies. No-choice mating trials in a greenhouse revealed reproductive isolation between host forms of P. glabricola and suggested female flies are capable of making oviposition mistakes resulting in adult offspring on the non-natal host. Based on these results, I used sequences of the nuclear gene EF-1α and AFLPs to genetically confirm host form status of the flies, and identify I. glabra as the ancestral host. In addition, genome scans revealed several loci under divergent selection among the hosts, suggesting the flies may be undergoing ecological speciation. To investigate the role host plants may play in the genetic divergence among flies, I first used AFLPs to confirm hybridization between I. coriacea and I. glabra. Hybridization rates differed across the geographic range of the species, which was also reflected in the morphology of the leaves. There were no general patterns, however, in the phenotypes of hybrid plants, and no single morphological trait that could reliably identify the hybrids. Finally, I combined genetic data of the flies and the plants to determine whether hybrid plants serve as bridges or barriers for the flies. Population comparisons revealed a significant positive relationship between hybridization in the plants and gene flow in the flies, and individual comparisons indicated flies are using the hybrid plants, albeit at low levels. The results suggest hybrids could serve as bridges between parental species, helping explain how a species from a typically monophagous lineage could expand its host range.