Cette thèse se propose d'appréhender le parcours du dramaturge américain Tennessee Williams en démontrant qu'il existe une authentique dimension engagée dans son œuvre. Ceci va à l'encontre de la critique traditionnelle qui tend à le dépeindre comme l'homme de la nostalgie et du rêve, le dramaturge apolitique du désir et des passions, en faisant abstraction du contexte idéologique. Or, Williams a commencé sa carrière dans les années trente comme écrivain protestataire en produisant de violentes pièces de dénonciation dans la tradition du théâtre de gauche. L'analyse de ces pièces écrites entre 1936 et 1938 – Candles to the Sun, Fugitive Kind, Spring Storm et Not About Nightingales – permet de rendre intelligible le parcours d'un dramaturge qui s'est toujours défini comme un révolutionnaire et revendique sa conscience sociale comme l'élément déterminant de son œuvre. Dans ces pièces, il intègre les stratégies formelles du théâtre de gauche comme le réalisme révolutionnaire ou l'esthétique du Front Populaire tout en créant des œuvres atypiques qui se distinguent de la production de l'époque. Préférant l'ambiguïté à des messages clairs ou didactiques, il inscrit ses premiers écrits sous le signe de la non clôture et joue avec les mécanismes identificatoires. Théâtre de l'émotionnel, son théâtre parait être à l'opposé de celui de Brecht. Pourtant son impact est souvent remarquablement similaire. C'est finalement en théorisant le phénomène des identifications fluctuantes que l'on peut comprendre la manière dont Williams s'approprie les fondements du théâtre de Brecht en en transposant les structures stéréoscopiques. Ceci nous conduit à redéfinir l'engagement au théâtre. / The object of my thesis is to reconsider the critical studies on Tennessee Williams by focusing on the political dimension of his early work. This is done by analysing the protest plays he wrote in the 1930s: Candles to the Sun, Fugitive Kind, Spring Storm and Not about Nightingales. These seminal plays reveal a virtually unknown Tennessee Williams, committed to fighting social injustice. This discovery is all the more important as the dramatist is often portrayed as an apolitical writer and described as a poet of the flesh and a depictor of sexual instincts and conflicts. This approach challenges the conventional vision of Williams' literary ambitions by showing that he may have been more socially and even politically subversive than generally admitted. A careful reading of Williams’s plays written in the thirties reveals that he closely followed the developments of left-wing theatre both in the choice of his subjects and of dramaturgical forms such as revolutionary realism or the aesthetics of the Popular Front. Still, he created original plays that went far beyond rigid formulaes or predictable plots. Because they propose no clearcut message, and through their permeating ambiguity and the feelings of empathy they trigger, these plays radically differ from the other productions of the period. Williams’ theatre could be described as a theatre of emotions at the opposite of Brecht’s theatre of alienation. However its impact is often remarkably similar. This can be explained by the phenomenon of fluctuating identifications that is Williams’s way of absorbing Brecht’s stereoscopic structures. This leads us to redefine the very principles of commitment in the theatre.

Singing is important for communication in birds. Some species of birds copy singing from other species. This heterospecific copying of singing is common especially in closely related bird species, and is usually called mixed singing in such cases. Mixed singing is often asymmetric, when only one species of the pair copies a song of the congener. The meaning of mixed singing is not well explained yet. The most common mechanism is probably an error during the learning phase of singing, but in some cases mixed singing can be adaptive. In my master's thesis I deal with the evolutionary meaning of mixed singing in two closely related passerine species - Common nightingale (Luscinia megarhynchos) and Thrush nightingale (Luscinia luscinia). These species co-occur in secondary contact zone in central and eastern part of Europe. Only Thrush nightingale which is larger and probably a more dominant species, exhibits mixed singing. In playback experiments in Common nightingale I studied a possible adaptive meaning of mixed singing in relation to interspecific communication. I tested the differences in behavioural and vocal response of Common nightingales to three types of stimuli: pure singing of Common nightingale, pure singing of Thrush nightingale and mixed singing of Thrush nightingale. The tested males...