Abstract
Virus discovery has long depended on the observation of outbreaks, and the research to understand their pathogenicity depended on their culture. The advances of sequencing technology and molecular biology tech-niques allowed researchers to discover the ubiquity and the diversity of viruses. Despite these advances, virus discovery remains mainly focused on vertebrate viruses. Furthermore, even the known diversity of these virus-es is poorly studied in term of virus ecology. Arthropods with their ancient evolutionary history represent 80% of animal diversity on our planet. The ubiquity of endosymbiosis in arthropods and their ability to support (sometimes multiple) symbionts suggest that their interactions with their viruses might be of symbi-otic nature, intimate long-term associations with outcomes ranging from mutualistic to antagonistic. In this context, this PhD dissertation focuses on a mosquito densovirus, Culex pipiens densovirus (CpDV), to in-vestigate their prevalence and diversity in natural populations of Culex pipiens mosquitoes and their inter-actions with endosymbiotic bacteria Wolbachia in a natural host-bacteria-virus system (Cx. pipiens -Wolbachia - CpDV) both in natural populations and laboratory colonies. We reveal a high prevalence and diversity of CpDV in worldwide Cx. pipiens populations. Moreover, CpDV persistently infects laboratory lines and are vertically transmitted along with their hosts’ endosymbiont Wolbachia. We reveal high CpDV prevalence and diversity in Turkey and Tunisia and further focus on these two countries to investigate Wolbachia-CpDV interactions in natural populations. In Tunisia, in a narrow contact zone where two ge-netically distinct Wolbachia groups coexist, different Wolbachia groups influences CpDV prevalence and diversity. Moreover, we show a positive correlation between Wolbachia density and CpDV density. Overall, our results suggests that CpDV-Cx.pipiens -Wolbachia system is a good model system to study the ecologi-cal interactions between these partners and their evolution together both in the nature and in laboratory conditions. Densoviruses with their diversity and long-term evolution with their hosts, and their easily ma-nipulated small genomes, are good models to study complex host-virus-bacteria interactions as well as virus ecology and evolution in a symbiotic context.