Thesis defence Sara Oukkal

Viral domestication and horizontal transfers in host-parasitoid systems

Jury composition:

Emmanuelle Jousselin, Reviewer 

Research Director, Centre de Biologie pour la Gestion des Populations, France

Anne-Nathalie Volkoff, Reviewer 

Research Director, INRAE - University of Montpellier, France

Martin Kaltenpoth, Reviewer (remote) 

Professor, Max Planck Institute for Chemical Ecology, Jena, Germany

Elisabeth Huguet, Examiner 

Professor, University of Tours, France

Cristina Vieira, Examiner 

Professor, Claude Bernard University Lyon 1, France

Abstract :

Eukaryotic genomes retain numerous traces of integrated viral sequences, remnants of ancient infections. Most of these sequences decay over generations; however, some have been preserved by natural selection and now serve useful functions to their hosts; a process known as viral domestication. In certain clades of parasitoid insects, whose larvae develop as parasites within a host, entire viral machineries have been domesticated. In these systems, genes of viral origin allow the production of “virus-like” particles that are injected into the host along with the egg. These particles suppress the host’s immune system, thereby facilitating parasitic development. This PhD work explores the origin, fate, and evolutionary consequences of viral sequences found in parasitoid insect genomes. It builds on a large genomic dataset established within our team, including numerous hymenopteran and dipteran parasitoids as well as their lepidopteran hosts from the Guanacaste Conservation Area (Costa Rica). Through bioinformatic analyses, this thesis investigates horizontal transfers from several perspectives: from exchanges between viruses and eukaryotes to virus-mediated transfers between eukaryotic species. Specifically, it examines: (1) parasitoid flies (Tachinidae) to search for new cases of viral domestication. (2) the origin and evolutionary history of Polydnaviruses (PDVs), one of the viral systems found in parasitoid wasps, and (3) the ability of PDV particles to mediate DNA transfer, leading to horizontal gene transfers between insects.