maenas (intertidal zone) and Segonzacia mesatlantica - Station ...

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182 CHAPITRE 5. ADAPTATIONS RESPIRATOIRES DE S. MESATLANTICA Abstract Segonzacia mesatlantica individuals were collected at deep-sea hydrothermal vents near the Azores Triple Junction and exposed to temperature and oxygenation changes in pressurized chambers. Both factors had a significant effect on hemolymph composition. At high temperature (20°C), magnesium levels and the hemocyanin hexamer proportion were higher than at low temperature (10°C), but hemocyanin content was higher at 10°C. Hemocyanin and calcium contents were also higher under high oxygenation. In all acclimated crabs, urate concentrations were higher compared to control. No lactate response was observed with an average basal level at 4 mM. Hemocyanin subunit composition was determined by ESI-MS under each experimental condition ; no evidence for phenotypic plasticity as a short-term adaptation was found under any of the experimental conditions used. Purified hemocyanin had a high affinity for O 2 , a strong Bohr effect, a strong L-lactate effect, but was insensitive to urate. The two former characteristics are typical of hydrothermal vent crustaceans, whereas the latter two are different from other hydrothermal crabs.
5.4. MANUSCRIT : RESPIRATORY ADAPTATIONS OF S. MESATLANTICA 183 5.4.1 Introduction Deep-sea hydrothermal vents are hypervariable environments in which the physical and chemical properties of the water exhibit rapid and large changes. These vents are located on geologically active zones such as oceanic spreading centers and subduction zones. Dense faunal assemblages live around hydrothermal vents, in contrast to the usually low biomass of the deep-sea environment. Such ecosystems rely on chemosynthetic bacteria for their primary production of organic carbon. Hydrothermal organisms live in the mixing zone between the hot, anoxic, acidic and toxic hydrothermal fluid and the cold oxygenated surrounding deep-sea water. The chaotic emission of hydrothermal fluid causes fluctuations of the environmental variables both spatially and temporally, thereby modulating oxygen availability. Since metabolic levels seem to be comparable between species from this environment and shallow water species (Childress, 1995), hydrothermal vent animals must cope with these conditions to maintain an adequate oxygenation of their tissues. Original respiratory adaptations are thus likely to exist in such environments (Hourdez et Lallier, 2007). Crustaceans are useful models for comparative physiology since they have colonized a wide range of environments (marine, freshwater, terrestrial), including deep-sea hydrothermal vents. Segonzacia mesatlantica is the only known endemic crab living on hydrothermal vents on the Mid-Atlantic Ridge. Like all other endemic deep-sea hydrothermal brachyuran species described up to now, it belongs to the Bythograeidae family. In decapod crustaceans, the respiratory pigment responsible for oxygen transport from the gills to the tissues is the blue copper-protein hemocyanin (Hc). Hc is made of non-covalent hexamers of 75 kDa subunits and can bind dioxygen reversibly on the two copper atoms of the active site of each subunit (Markl et Decker, 1992). Different subunit types exist for each species thus permitting potential combinatory diversity of the complexes. Hc is freely dissolved in the hemolymph and its functional properties can be modulated by a wide range of effectors (pH, temperature, divalent cations, L-lactate, urate, thiosulfate) (Bridges, 2001). The phenotypic plasticity due to the different subunit types can also result in changes in the intrinsic affinity of the pigment for O 2 (Giomi et Beltramini, 2007). All these regulatory mechanisms of Hc affinity enable crustaceans to adjust the functional properties of their pigment to a variety of stressful conditions (hypoxia, high temperature, exercise, terrestrial way of life). Crustacean Hc affinity usually decreases with decreasing pH (normal Bohr effect) and with in-
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THESE DE DOCTORAT DE L’UNIVERSITE
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i Résumé / Abstract Réponse adap
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iv SOMMAIRE 4.2 Objectifs de l’é
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FIG. 1.5 - Localisation des princip
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(a) FIG. 1.6 - Fonctionnement d’u
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104 CHAPITRE 3. STRUCTURE DE L’HC
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233 Modèle 2 : 2 sous-unités lég
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235 1 0.9 0.8 6 s-u aléatoires 2 s
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Bibliographie Adair, G. S. The hemo
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BIBLIOGRAPHIE 239 Catalina, M. I.,
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BIBLIOGRAPHIE 241 Farmer, C. S., J.
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BIBLIOGRAPHIE 243 Hourdez, S. Adapt
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BIBLIOGRAPHIE 245 Mangum, C. P. Sub
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BIBLIOGRAPHIE 247 Rainer, J., C. P.
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BIBLIOGRAPHIE 249 Svedberg, T. et I
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BIBLIOGRAPHIE 251 Vanin, S., E. Neg
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Liste des figures 1.1 Cycle des mar
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LISTE DES FIGURES 255 4.17 Profils
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Table des matières Résumé Sommai
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TABLE DES MATIÈRES 261 4.3.5 Spect
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TABLE DES MATIÈRES 263 Table des m
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