Soutenance d'HDR de Steven Ramm (Ecobio) - OSERen, Salle De Conférences, RDC Bât.14B, Campus De Beaulieu De L'Université De Rennes

Sperm competition has provided a conceptual framework to study the evolution of male reproductive phenotypes for more than fifty years. In the first part of this thesis, I document how my research has established the scope and importance of this selection pressure – together with the associated forces of sexual selection and sexual conflict – acting on a diverse array of reproductive traits including sperm, spermatogenesis, seminal fluid, genitalia and copulatory behaviour across multiple taxonomic groups, most notably my primary model systems of mammals and flatworms. In the second part of the thesis, I then explore the unique ability of hermaphrodites to reproduce via self-fertilization; the circumstances of low mate availability (and consequently absent sperm competition) in which they might typically choose to do so; and what the immediate and evolutionary consequences of such a switch might entail. Finally, I recognise the importance of abiotic as well as biotic factors in driving reproductive trait evolution, an increasingly important consideration under climate change. A common theme linking all three parts is the important role of genotype-environment interactions in determining patterns of variation and plasticity within populations and in shaping evolutionary trajectories.