Résumé
Life's vast diversity is largely shaped by sexual selection, where competition for mates drives the evolution of extraordinary traits across species. In this thesis, I first explored the comparative evolution of the appearance of weaverbird nest structure, an extremely intricate extended phenotype that could evolve through sexual selection. I tried to determine whether weaving patterns could evolve through sensory drive mediated by the processing bias mechanism and found mixed support for this hypothesis. Secondly, I focused on bird song, an iconic trait often associated with mating success, using comparative and meta-analytical approaches. I aimed to understand the determinants of the evolution of song diversity in weaverbirds and to identify common principles that might explain why, in songbirds, song diversity seems to be selected in some species but not in others. I discovered that, in weaverbirds, song diversity does not appear to be driven by the intensity of sexual selection but rather by colony size. By contrast, our meta-analysis in songbirds shows that song diversity covaries with the intensity of sexual selection, being more closely linked to intersexual than intrasexual selection, which could explain why stronger selection on song diversity is observed in some species compared to others. Together, these results highlight the multifaceted nature of trait evolution, demonstrating that sexual selection, social selection, and ecological factors play crucial roles in shaping the diversity of elaborate traits over an evolutionary time scale.