• ciliates
• Ciliophora
• evolution
• genomic analysis
• Holospora
• Holosporales
• Paramecium
• symbiont
• symbiosis
• variant calling

Holospora undulata is an obligate endonuclear symbiont of the ciliate Paramecium caudatum, and it belongs to the class Alphaproteobacteria. It has a complex life cycle, with two forms: the reproductive form (RF), which survives and divides only within the host nucleus, and the infective form (IF), which can survive outside the host and infect new ones. This symbiont is transmitted both vertically to the offspring, during mitotic reproduction of the host, and horizontally, with release of IFs and new hosts’ infection. The Experimental Evolution of Communities research group at the University of Montpellier conducted long-term evolution experiments to study how range expansion of the host influences host-symbiont evolution. They found that symbionts in dispersing ciliates evolved lower virulence and higher transmission rate compared to the unevolved controls. The purpose of this thesis was to compare genomic data from selected and control lines of H. undulata. In the present analysis, DNA from cryopreserved samples, taken during the experiment, were amplified via Whole Genome Amplification and sequenced via Illumina technology. The analysis included assembling the ancestral genome and performing variant calling, revealing significant differences between selection and control treatment and identifying unique variants in the selected lines, potentially linked to evolutionary changes.