No description available.

Endosymbiosis has been a major driver of evolutionary diversification of eukaryotes. However, symbiosis can create conflict between partners and symbiont density is often tightly regulated within hosts to ensure optimal functioning of the holobiont. The horticultural pest insects, citrus mealybugs, make an intriguing and potentially-powerful case study for endosymbiosis, harbouring two obligate, nutritional, vertically transmitted bacteria: Tremblaya princeps and Moranella endobia, in a nested mutualism. In this thesis, I examine the variation in the density of each of these obligate symbionts in citrus mealybugs under controlled environmental conditions, using qPCR, as well as the diversity of facultative symbionts that infect the mealybugs using next-generation sequencing and conventional targeted PCR. Citrus mealybugs were found to harbour Wolbachia, Spiroplasma, Cardinium and Rickettsia, which have been found to impact the fitness of their hosts in other insect species, whereas long-tailed mealybugs were not found to harbour any of these bacteria, but the symbiont communities in both species were found to be dominated by their obligate symbionts. The density of the two obligate symbionts varied by up to six-fold between different populations kept under identical environmental conditions and a hybridisation experiment indicated that M. endobia and T. princeps density may be controlled by symbiont and host genotype respectively. However, symbiont density was not found to correlate with life-history traits in the laboratory, the ability of mealybugs to exploit different plant species, or the susceptibility of the mealybugs to insecticide and artificial reduction of symbiont density by heat-stress also had no effect on host fitness. Citrus mealybugs harbour seemingly superfluous symbionts with no clear fitness costs or benefits.

Heritable bacterial symbionts are astonishingly common in insects, yet relatively little is known about how heritable symbionts influence the biology of social insects such as ants, bees, wasps and termites. In this thesis I investigate various aspects of the biology of heritable symbionts in social insects, principally focusing on the relationship between ants, the largest group of social insects, and the symbiont Wolbachia, the archetypal reproductive parasite. In Chapter 1, I begin by reviewing the biology of Wolbachia. In Chapter 2, I show that the sex, caste and size of an individual's colony determine the likelihood that it is infected with Wolbachia, and I provide correlational evidence that Wolbachia provides small increases in colony productivity in the ant Temnothorax crassispinus. In Chapter 3, I combine colony censuses and antibiotic treatment experiments, finding that Wolbachia neither distorts host sex ratios nor causes strong female mortality type mating incompatibilities in the ant Myrmica scabrinodis. In Chapter 4, I critically evaluate the theory that heritable symbionts should evolve to manipulate caste-fate in social insects, outlining three distinct evolutionary scenarios under which this might occur. In Chapter 5, I provide evidence for negative interactions between Wolbachia and both Spiroplasma and Arsenophonus in M. scabrinodis hosts, and I show that multiple unrelated strains of both Wolbachia and Spiroplasma occur across the Palaearctic. In Chapter 6, I show that one of two strains of Wolbachia infecting the ant Monomorium pharaonis was acquired by hybrid introgression. In Chapter 7, I find that ant species with limited queen dispersal are almost twice as likely to be infected with Wolbachia relative to other ant species, supporting the hypothesis that population structure influences the invasion ability of Wolbachia. Finally, in Chapter 8, I discuss the broader significance of my findings.

Mechanisms associated with growth regulation have been shown to be highly conserved in mammals and Drosophila, especially when examining the insulin signalling pathway. Previous studies suggest that nitric oxide (NO) signalling can inhibit growth and cell proliferation in a Drosophila forkhead box O (dFOXO)- dependent manner. dFOXO is a component of the insulin signalling pathway and has also been demonstrated to inhibit growth via its interactions with components in this pathway; however, the mechanism by which dFOXO and NO interact is unclear. Since inhibition of growth by NO is dependent on dFOXO, this thesis examines the effect of co-expressing nitric oxide synthase II (NOS2) with three dFOXO alleles (dFOXO25, dFOXO21 and dFOXOBG01018) in Drosophila salivary glands taken from third instar larvae. It concludes that the dFOXO25 null allele appeared to be the strongest deletion of dFOXO given that salivary gland nuclei appear most similar in size to the wild type. This indicates that NO-induced growth inhibition only occurred to a very small degree as a result of a powerful loss-of-function of dFOXO exhibited in dFOXO25 homozygotes. This thesis also investigates the effects of NO on salivary glands taken from the same developmental stage when co-expressed with overexpressed oncogenes, dMyc and RasV12. Nuclei measurements were larger than the NOS2-only expressing line and smaller than the lines expressing only each of the oncogenes. However, TEM analysis revealed that co-expression might induce endoplasmic reticulum (ER) stress in the glands. Research shows that NO and these oncogenes can provide the reactants necessary to generate peroxynitrite, which is associated with the generation of ER stress. When examining the effects of these growth regulators on mitochondria and Golgi, this thesis reports that dFOXO, NOS2 and dMyc can increase mitochondrial biogenesis. Golgi was unaffected by expression of the growth regulators.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1982. / Vita. Abstract. Includes bibliographical references (leaves 76-85). Also available via the Internet.

Thesis (Ph.D.) - Simon Fraser University, 2005. / Theses ( Dept. of Biological Sciences) / Simon Fraser University. Includes bibliographical references. Also issued in digital format and available on the World Wide Web.

Thesis (Ph. D.)--University of Chicago, Dept. of Molecular Genetics and Cell Biology, 2001. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 89-93). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Oklahoma, 1999. / Includes bibliographical references.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.