Evolution and Transition of Mating Systems : Two Case Studies

Abstract

Mating system transitions are frequently observed in nature, profoundly shaping the genetic architecture and evolutionary trajectories of populations. Yet, the genomic mechanisms underpinning these transitions and their subsequent consequences remain incompletely understood. In this thesis, we aimed to elucidate the genomic factors influencing mating system evolution and transition by employing numerical simulations, and bioinformatic analyses. We specifically focused on two organisms, the plant Phillyrea angustifolia and the nematode Caenorhabditis elegans. In Phillyrea, we developed numerical adaptive dynamic models to investigate how male-favoring sex ratio distortion influences the transition from hermaphroditism to dioecy. Our results reveal a critical threshold in the intensity of distortion that triggers this transition, indicating the sensitivity of hermaphrodite sex allocation strategies. Complementing this, bioinformatic analyses was carried out to study the pollen allergen gene family that potentially governs the sex determination X hermaphroditic self-incompatibility interaction in Phillyrea. We uncovered new gene members as well as signatures of duplication in this gene family’s evolution. For C. elegans, individual-based simulations using SLiM software revealed how mating system variation affects sexually antagonistic polymorphism across genomes. We demonstrated that self-fertilization accelerates polymorphism loss, particularly selecting alleles beneficial to hermaphrodites. Collectively, these findings enhance our understanding of how mating system dynamics interplay with genome evolution, highlighting the critical role of genetic conflicts and reproductive strategies in shaping genetic diversity.