Thèse de doctorat en Evolution moléculaire et adaptation
Sous la direction de Stéphane Hourdez.
Soutenue en 2009
à Paris 6 .
Evolution des adaptations respiratoires chez les Polynoidae (Polychaeta) des sources hydrothermales
Pas de résumé disponible.
Hydrothermal vents (HV) are deep-sea ecosystems where hypoxia/anoxia is one of the major constraints. Respiratory pigments play a key function in the adaptation to hypoxia. HV polynoids are abundant, diverse and widely distributed and are the only ones to possess hemoglobins (Hb), and these are unique among annelids. The goal of this work was to know their evolutionary history. There are 2 types of Hb in HV polynoids: 1- and 4-domains. While they are extracellular, they are more related to intracellular globins that to annelid extracellular ones, indicating a distinct origin. We studied the evolutionary history of the 4-domain gene Hb and found that originated from the tandem duplication of a myoglobin-like ancestral. Both globin types possess residues in the heme pocket that are responsible for the high oxygen affinity in other organisms' Hb. But the adaptive value of these Hb probably resides in their expression at high levels. Plus, some amino acid sites were shown to be under positive selection (PS). Some are located in the heme pocket where they might affect functional properties. Others are in areas where they can affect interactions between subunits and domains.