Topic: Diversity and evolutionary history of the bacterial symbiont Serratia symbiotica in the pea aphid (Acyrthosiphon pisum)
Dates: 1 Octobre 2026 – 30 September 2029
CBGP supervisor: E. Jousselin

Moana Castanier’s PhD project aims to reconstruct the history and mechanisms of diversification and ecological specialisation in the pea aphid, Acyrthosiphon pisum. Using individual whole-genome sequencing data, the first objective will be to reconstruct the history of diversification by combining global-scale phylogeographic approaches with demographic inferences. These analyses will help to determine the role of adaptation to the host plant in diversification, to test whether specialised lineages have a single or multiple origins, and to estimate the rate and context of their formation.

In addition to nuclear genomes, the analysis of bacterial endosymbiont genomes will enable us to reconstruct the history of the associations between aphids, their host plants and their endosymbionts. A second objective will be to study the genetic basis of adaptation to the host plant, using as comparative frameworks: (i) populations adapted to different host plants and (ii) populations adapted to the same host plant but of distinct geographical origins in Western Europe and Central Asia (biological replicates). Finally, a third objective will be to develop a phylogenomic approach extended to the genus Acyrthosiphon in order to assess whether patterns of specialisation with regard to host plants are also evident at this evolutionary scale.