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Thesis started, 2016, Defended in june, 2020 12^th
Fund:  MESR
Direction: Yannick Outreman, Jean-Christophe Simon

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Abstract

Symbiotic associations between an eukaryotic host and a microbial symbiont are ubiquitous. Symbiosis is often associated with the modification of hosts’ phenotypes, referred to as extended phenotypes. The objective of this thesis is to better understand how extended phenotypes and in particular modulation of host behaviors caused by symbionts can influence the biotic interactions of insects. In particular, we focus on the effect of the symbiotic bacteria of a phytophagous insect, the pea aphid Acyrthosiphon pisum, on its relationships with its host plant and one of its natural enemies, the parasitoid Aphidius ervi. Our studies suggest a limited influence of Hamiltonella defensa and Regiella insecticola on host behaviors involved in foraging and plant selection. However, our results show that symbiotic microorganisms play an important role in aphid-natural enemy relationships. Aphids infected with H. defensa exhibit less defensive behaviors, while the protection phenotype and the costs associated with the symbiont vary from one symbiont species and strain to the other. These various works show that the impact of symbionts on behaviors is highly variable and depends on the host-symbiont association. This thesis provides a better understanding of the evolutionary forces involved in the dynamic of symbiont associations and as well as on the role of symbionts in the ecology and evolution of their host species.

Poster pdf