Recently, there has been growing awareness that many animals and plants harbour bacterial symbionts that help protect them against natural enemies. The mushroom-breeding fly Drosophila neotestacea is commonly infected with a virulent parasitic nematode, Howardula aoronymphium. Infections are severe, reducing adult survival and mating success, and until recently virtually all females were rendered sterile. We have discovered that D. neotestacea harbours a strain of the bacterial symbiont Spiroplasma that restores fertility to nematode-parasitized female flies. Spiroplasma appears to be both increasing in frequency and spreading westward across N. America. My thesis examines associations between flies, nematodes and Spiroplasma in British Columbia, which appears to lie at the edge of the range of advancing Spiroplasma infections. I identified Spiroplasma-infected flies in British Columbia for the first time. Sequencing a number of Spiroplasma genes, as well as fly mitochondrial DNA, strongly suggests that the defensive symbiont is spreading westward. Furthermore, high nematode infection rates in BC, as well as laboratory experiments demonstrating the ability of Spiroplasma to restore fertility to nematode-parasitized BC flies, suggest that there is a strong selective pressure for Spiroplasma to continue to spread in BC. I also examined the generality of Spiroplasma-mediated defense by exposing flies to a gram-negative bacterial pathogen, Pectobacterium carotovorum. Exposure dramatically reduced survival regardless of Spiroplasma infection, suggesting that Spiroplasma does not defend against gram-negative bacteria. / Graduate / 0718

Endosymbiosis is a pervasive phenomenon that has been a powerful force in insect evolution. In many well studied insect-bacterial associations, the bacteria can serve as reproductive manipulators, nutritional mutualists or defenders of their hosts. Fungi are also frequently associated with insects, and initial estimates suggest that these fungi are hyperdiverse. Saving a handful of examples, however, the functions of these fungi within insect hosts are largely unknown. This dissertation begins with a review that lays the conceptual groundwork for understanding bacterial and fungal endosymbiosis in insects. I make predictions about why one versus the other microbe might serve the insect, given any unique physiological, ecological or evolutionary conditions. I then aim to derive insights about microbial symbiosis by focusing on a particular system, that of brownbanded cockroaches, Supella longipalpa (Blattaria: Blattellidae) and their specialist wasp parasitoids, Comperia merceti (Hymenoptera: Encyrtidae). Here, I identify the symbiotic community of these two insects by using both culture-dependent and independent methods to characterize the vertically transmitted bacterial and fungal associates. Finally, I show that a heritable fungus in C. merceti, long presumed to be a mutualist, is parasitic under laboratory conditions: infected wasps incur fitness costs for housing the fungal symbiont relative to uninfected wasps. Additionally, although the fungus is not horizontally transmitted sexually, it is readily horizontally transmitted from the offspring of infected females to those of uninfected females that are using the same host.

No description available.

This thesis attempts to broaden what is known about bacterial symbionts within amoebae by the use of a number of different molecular methods. Initially a number of different amoeba strains were screened for bacterial symbionts by 16S rRNA gene PCR, then the symbionts were identified by comparative sequence analysis and phylogenetic analysis. The amoeba strains containing bacterial symbionts were characterised by cell morphology, 18S rRNA gene sequencing, internal transcribed spacer sequencing and allozyme electrophoresis. Amoebae belonging to the genera Acanthamoeba, Naegleria, Ripidomyxa and Saccamoeba were identified as containing symbionts that belonged to a wide range of different bacterial genera. Relationships between bacterial symbionts and their host amoebae were analysed by the use of transmission electron microscopy and fluorescent in situ hybridisation using symbiont specific probes. Also described are attempts that were made to isolate and grow the bacterial symbionts outside of their host amoebae as well as experiments to try to transfer bacterial symbionts from one amoeba strain to another. Lastly the results from this study are discussed as a whole to put into perspective how they contribute to the body of knowledge of symbionts within protozoa.

Les invasions biologiques ont des conséquences écologiques telles que l'émergence de pathogènes et de ravageurs. Les populations invasives font face à de nouvelles conditions biotiques et abiotiques qu'elles doivent surmonter. Ces invasions biologiques sont des systèmes modèles pour étudier l'évolution sur de courtes échelles de temps car elles nécessitent une adaptation rapide qui fait intervenir différents processus (sélection naturelle, dérive, plasticité phénotypique). Du fait des introductions multiples et de l'hybridation, une augmentation de la variabilité génétique nucléaire peut-être observée dans ces populations, support d'une réponse adaptative plus rapide. De plus, chez les insectes, les symbiotes peuvent jouer un rôle important dans l'adaptation, contribution encore largement inconnue. Le ravageur de culture Bemisia tabaci est un complexe d'espèces dont les barrières reproductives sont peu connues et dont les différentes entités --- les cytotypes --- présentent des cortèges symbiotiques qui leur sont spécifiques. Grâce à une description de la dynamique spatio-temporelle de ces cytotypes, en contexte invasif en France et plus largement dans le bassin méditerranéen, nous avons constaté la présence simultanée de deux de ces entités et nous nous sommes interrogés sur un éventuel remplacement ou une coexistence. Cette situation originale nous a permis de tester leurs limites reproductives grâce à des microsatellites et des tests comportementaux, ainsi que la possibilité de transferts horizontaux de bactéries. Transferts que nous avons tenté de reproduire en laboratoire. Nous avons aussi développé des marqueurs RADSeq pour de futures analyses génomiques / Biological invasions have ecological consequences such as the emergence of pathogens and pests. Invasive populations face new biotic and abiotic conditions that they have to overcome.These biological invasions are model systems to study the evolution over short time scales because they require rapid adaptation that involves different processes (natural selection, drift, phenotypic plasticity).Because multiple introductions and hybridization, an increase in the nuclear genetic variability may be observed in these populations, supporting a faster adaptive response.Moreover, in insects, symbionts can play an important role in adaptation, a contribution largely unknown yet.Bemisia tabaci crop pest is a complex of species whose reproductive barriers are poorly known and whose different entities --- the cytotypes --- have symbiotic associations specific to them.Through a spatio-temporal dynamics description of these cytotypes in invasive context in France and more widely in the Mediterranean bassin, we found the simultaneous presence of both of these entities and we wondered about a possible replacement or coexistence.This peculiar situation has allowed us to test their reproductive boundaries with microsatellites and behavioral tests, as well as the possibility of horizontal transfer of bacteria. Transfers that we tried to reproduce in the laboratory. We have also developed RADSeq markers for future genomic analyzes

En raison de leur rôle central dans la physiologie et le développement des plantes, les phythormones ont depuis longtemps été considérées comme des médiateurs chimiques déterminants dans la capacité des insectes à contrôler leur environnement végétal. Les mécanismes permettant aux insectes de manipuler la balance phytohormonale permettant ainsi la régulation des apports nutritifs et la modulation des défenses végétales demeurent néanmoins pour la plupart inconnus, en particulier pour les insectes galligènes et mineurs de feuilles. L’objectif de ma thèse visait à caractériser les capacités de modulation phytohormonale par les insectes manipulateurs de plantes avec un accent particulier sur le lépidoptère mineur de feuille Phyllonorycter blancardella. Nous avons ainsi développés une caractérisation spatio-temporelle de la réponse des plantes aux attaques des larves mineuses au niveau moléculaire et biochimique. Une comparaison entre différents systèmes biologiques nous a permis d’évaluer les similitudes entre les stratégies adoptées par les les insectes galligènes et les insectes mineurs de feuilles, d’identifier l’origine possible des phytohormones impliquées dans la manipulation de la plante et le rôle des bactéries endosymbiotiques d’insectes dans ces interactions. / Because phytohormones lie at the very core of molecular mechanisms controlling the plant physiology and development, they have long been hypothesized to be involved in insect-induced plant manipulations. Insects are using phytohormones to manipulate their host plants for their own benefit, regulating nutrient provisioning and plant defenses. However, a mechanistic understanding of how phytohormones operate in plant reconfigurations by plant-manipulating insects, especially by gall-inducing and leaf-minging insects, is lacking. The objective of my Ph.D. was to provide an extensive characterization of how plant-manipulating insects modulate the plant global hormonal balance with a specific focus on the leaf-mining moth Phyllonorycter blancardella. We thus developed a time course characterization of plant transcriptomic and biochemical responses following attack by leaf-mining larvae. A comparative analysis between different biological systems allowed us to estimate similarities in strategies developed leaf-mining and gall-inducing insects, to identify the possible origin of phytohormones involved in the plant manipulation and to estimate the role of insect endosymbiotic bacteria in these interactions.